Zel's Motoring Adventures...Volvo, Renault, Rover, Trabant, Invacar & A Sinclair C5 - Updated 13/11.

[Zelandeth]

Decided to attack a job I'd been putting off for a while this afternoon.  Attempt number 2 at making the driver's door on the Jag something vaguely resembling weather proof.

After about an hour and a lot of swearing later...

We will have to see.  Doing anything further requires me to remove the electric window mechanism and I'd really rather not mess with that if I don't have to.

Wouldn't *need* to mess around with this of course if whoever replaced the window motor had just put the original weatherproofing back in place (it was bundled up in a ball in the bottom of the door).

There's a contiguous piece from the top to bottom of the door the whole way along except for where there's an "n" shaped cutout to go around the window motor mechanism...and it's inboard of the wing mirror and window glass which should be the only places significant water should get in.  In theory.

There's an extra layer behind the door handle and speaker areas because they're where most of the water was appearing in the cabin.

Not really visible, but I finally replaced the missing screw holding the lens on this light.

Which hopefully means it won't fall off about every tenth time the door is closed now.

Really hope the water stays put now as I *really* don't want to have to take the electric window apart.

Oh...forgot to originally include...why didn't someone tell me I was being a blind idiot when I missed that the wiper arms on the Jag are sided?

Sitting at a far more sensible level now I think.

[Ben_O]

Regarding brake cleaner, if you use a lot of it, have you considered buying it in 5ltr containers to then decant into a pump spray bottle?

Might work out more economical for you than the aerosol tins.

[Zelandeth]

1 hour ago, Ben_O said:

Regarding brake cleaner, if you use a lot of it, have you considered buying it in 5ltr containers to then decant into a pump spray bottle?

Might work out more economical for you than the aerosol tins.

Something I'll need to have a think about.  At the moment storage is an issue as it's easier to cram aerosol cans into corners in the garage than 5 litre bottles!

Definitely is on "the list" for things to look at when (if) the garage finally gets sorted out.

[Zelandeth]

How am I ever going to tell which car is mine out here...Oh...wait...

I get the impression that while it may have taken a while for us to tick over the first thousand miles the second one will take anywhere near as long...

One of the bits of trim fell off the inside of the offside door last time out, so today I decided to call time on the spray adhesive and got some old school goop involved.

Then wedged it firmly in place.

I reckon this will stay stuck a lot better.  Can see me redoing most of these in the same way at some point.  Summer will be the real tell when things get warm.

Also on the subject of doors...I completely randomly spotted today that the weatherstrip between the two sliding window panes on the nearside (the offside one is missing) was installed backwards...I apparently totally failed to notice that there was a plastic side and a felt side when I installed it.  Does a far better job of stopping the draught when the window is closed now!

Only took me approximately two years to notice.  Ten points for observation to me.

Annoyingly it appears that even with the level sorted that we do still have a slight oil leak.  It looks like it *might* be actually coming from the oil pressure switch as the whole area around it looks a bit wet.

Have given the general area a good spray down with degreaser so we can have another look after the next trip out to see if it's the culprit.  Would be nice as it's a cheap and easy part to change.

Not holding my breath though...My gut feeling is that we're looking at a leak from the crankshaft oil seal.

The belts are in a state as you can see too.  They have been loose for a while now...but lately have been getting a bit ridiculous.  Aside from the increasingly unhappy squeak every time the starter is operated from cold, it's never good when you can SEE how slack a belt is.

Yes, that is as floppy as it looks.  Especially the one nearest the camera.

The reason I hadn't done something about this sooner was simple: I'd been completely and utterly unable thus far to shift the nut on the Dynastart pulley.  The belt tension on this engine is adjusted (like on old VWs) by adding or removing shims between the pulley sheaves...so any tension adjustment involves removing that big nut.  While there are two holes in the fan to allow you to wedge it in place - the nut was tight enough that these holes were ovalling out from the torque I was applying. 

Right up until the point that I *finally* spent an hour turning the back of the garage upside down and unearthing the impact gun.

In approximately 0.3 seconds it buzzed it straight off without it seemed like any effort whatsoever...Didn't even have to lock the pulley...

Sometimes you just need the right tool for the job at hand.

It's not a tool you'll use for every job (and using it for the wrong one can cause you no end of headaches...), but really is an absolute godsend when presented with something like this or trying to get a wheel nut that's been done up by Kwik-Fit to 10,000,000,000 times more tightly than it needed to be.  This was less than £50 and for the three jobs I've really used it for so far I reckon has already more than paid for itself in saved time, sweat and spilled blood.  Just make sure if you get one to get a good quality set of sockets to go with it.

The other reason I wanted to get this lot apart was so that I could actually clean up the pulley running surfaces...After this engine had spent a good number of years sitting outside in the weather they were unsurprisingly in quite a state - I'm honestly surprised that the belts didn't just self destruct given the state these were in.

Definitely beyond the point of "self cleaning" at this point...so out with the carbide mop.  Realistically  I could do with a new set of pulley sheaves, but the heavy, rough pitting that will shred belts is gone at least.  I do have a friend with a lathe so might have a chat to see if it would be possible to use that to knock some of the crud off.

The fan hub (which forms the rear face of the pulley) got the same treatment.

Again...It really has seen better days, but is a lot better than it was.

The belts will want replacement now as running on the pulleys in that state has unsurprisingly wrecked them.  I'll grab a new pair next time I'm in the vicinity of Motorserv.   They're not exotic or expensive so I'm not worried about that.  They are at least properly tensioned now though (if anything a little over-tight in the case of the front belt).

Not really too worried - they'll be getting replaced shortly anyway - I'll spend a bit of time ensuring that the replacements are tensioned as close to as per the manual as possible.

Quick test revealed that the "chirp" on activating the starter is indeed now gone.

I had also completely failed to appreciate quite how much noise the belts were making at high engine speeds...The engine is SO much quieter and smoother when revved now.  Will be interesting to see if that's at all obvious when on the move - though given that about 85% of the noise you're aware of is CVT and gearbox I rather doubt it.

Will probably be making a run up to Pleiades later this week to pick up a couple of hydraulic lines for the BX (been a couple of weeks since I touched it and that's starting to nag at me).  About an hour's run each way according to Google, adds ten minutes to avoid motorways.

I'm very tempted to take TPA for that trip.  Seriously tempted...Xantia makes by far the most sense (Jag isn't going that far until I properly track down the infuriatingly intermittent charging problem), but I think it's really about time I took TPA on a decent run.

Speaking of the Xantia...I *need* to figure out why the boot won't open, plus I need to give it a service.  Just struggling to find enthusiasm for it a bit lately.  Think that happens when you've owned any car for a few years, there are high spots and low spots periodically, and I'm in one of those with it at the moment.  Can't see me moving her on though unless someone offered a swap for a solid Cherokee (which will never happen as said Cherokee is worth about five times more than the Xantia even without the current niggles) anyway.  Just too competent a car for that.  Oh...or a Renault 25.  Would have to be a pre-facelift car though... preferably a Monaco.

Seriously, I just need a bloody aircraft hanger so I can just buy one of everything that's on my wish list without having to get rid of stuff!

[Zelandeth]

Decided to have a better shot at cleaning the Dynastart pulleys up on TPA. 

There is deep enough pitting that they'll never be perfect, though I think this should be good enough for the job...given that the previous belts lasted the best part of a thousand miles and still worked once the tension was adjusted...if I go through £14 of belts once a year or so I'm really not going to lose any sleep over it.

Sadly Motorserv only had one belt (Gates 6262MC for reference) so I'll need to swing by tomorrow to pick up the second one before I can fnish reassembly.

[dollywobbler]

On 4/14/2021 at 4:53 PM, Zelandeth said:

Well let's monitor the Invacar oil leak now I've resolved this.

Dumb mechanic error.  Guessing I forgot to thread the dipstick in to take the reading.  Let's see if this has sorted it next time we're out.

Only real car job was to finish sorting the wipers on the Jag.  When I sorted out the intermittent motor back last year I never really put any effort into getting the wiper alignment right and had broken the non return valve for the windscreen washers.  Both of these issues were resolved today, so the wipers now park in the correct spot again, so only a quarter of the way rather than halfway up the windscreen.

Replaced the wiper blades too as the ones on there looked horrible.  They went rusty pretty much the day they were fitted.

Last job was to realign the washer jets as the driver's side one washed the scuttle and the passenger side one was pointing skywards.

Much better.  Granted that's one item of about 700 on the to do list ticked off...but it's something at least!

Sorry to be a pain, but shouldn't the curved arm be on the passenger side? 

[dollywobbler]

Oh balls. You've already sorted it. Sorry, playing catch up!

Good work on the Invacar. Don't forget aircooled engines can be good at spreading oil around. My leak was very bad from the oil cooler seals, but because if the airflow, the oil went everywhere!

[Zelandeth]

3 hours ago, dollywobbler said:

Oh balls. You've already sorted it. Sorry, playing catch up!

Good work on the Invacar. Don't forget aircooled engines can be good at spreading oil around. My leak was very bad from the oil cooler seals, but because if the airflow, the oil went everywhere!

Can you do me a favour?

Could you grab a hold of the crankshaft pulley on TWC and see if there's any detectable fore and aft play?  I can feel a distinct "clonk" doing that on TPA, but given the slightly odd clutch/drive setup I don't know if that's just to be expected.

I'll actually measure it at some point shortly, but it's something I've been meaning to ask about pretty much since since the day I revived this engine!

[dollywobbler]

I'll try to remember next time I'm at the unit. Currently in Derbyshire.

[Zelandeth]

Task number 1 today... changing rear spheres on the Xantia.  Want this done so I can drop the sphere removal tool back off with its owner.  I hate having other people's tools on loan for longer than absolutely necessary as I'm paranoid about losing them.

Dodged the usual game of chasing the ramps around by doing the job on the lawn.  They dig in enough there to stay put.

Of course because it's the Activa there's a hydraulic line in precisely the most awkward place when you're trying to get the tool onto the sphere.

Not enough to be a problem, just enough to be moderately annoying.

Offside one first, wound off without too much of a fight.

Only slight game I had there was the seal vanishing into another dimension (I did find it eventually) which had me second guessing if I'd got the old one out of the strut for a few minutes.  New one in.  That's this side done.

Nearside required a little more persuasion to shift, but I was still able to do it by hand just using the sphere tool.  Didn't need to get any additional breaker bar or anything involved.  It's really nice working on a car where the previous owner or a garage haven't overtightened absolutely everything.

New sphere on.

Tightened the bleed screw on the regulator back up, checked for leaks then that's that job done.  Maybe 20 minutes?

Well it would be if the new spheres weren't dud.  Knew it was a bit of a risk being NOS ones from 1998...but was worth a shot.  Offside one is passable, nearside one though is just as bad as the one that came off.

No huge inconvenience really, as mentioned above they take about 20 minutes to change and they were given to me free, so I'm really not that irked.  Just would have been nice to get it done in one hit.

We'll be playing this game again shortly then!

 

Second new belt was picked up for TPA today so those have now been fitted.  Adjustment seems spot on with the six spacers split evenly with three on each side.

Glad to report that the re-stuck bit of door trim has indeed stayed stuck.

On the subject of trim, while getting the whole roof lined is definitely a job for "sometime in the future" one bit I really wanted to address was the rear C pillar on the offside, mainly because of an unsightly historic repair there.

Conveniently I had a couple of offcuts left from when I did the carpeting job which I was fed up of shuffling from place to place in the garage.  They were just big enough to do this.

Far tidier!

Obviously made a matching one for the other side too.

Have left them both wedged in place while the glue sets.  I'd really like to replace the windscreen demister duct, however it's still a way down the list - especially at £25+ a metre!

 

[LightBulbFun]

18 minutes ago, Zelandeth said:

Conveniently I had a couple of offcuts left from when I did the carpeting job which I was fed up of shuffling from place to place in the garage.  They were just big enough to do this.

Oh that reminds me!

that terry clip you where wondering about, im pretty sure was for the original fire extinguisher included with the car back in 1973

if you look at the drawings from the workshop manual they show something in the same place as that clip which im pretty sure is the fire extinguisher  

(which iv heard described as an aerosol type, did not realise they meant it literally in that it was the size of like a rattle can! LOL)

[bobdisk]

11 hours ago, Zelandeth said:

Well it would be if the new spheres weren't dud.  Knew it was a bit of a risk being NOS ones from 1998...but was worth a shot.  Offside one is passable, nearside one though is just as bad as the one that came off.

No huge inconvenience really, as mentioned above they take about 20 minutes to change and they were given to me free, so I'm really not that irked.  Just would have been nice to get it done in one hit.

We'll be playing this game again shortly then!

Always always be careful of nos parts. See my post on the Daf Owners forum:

https://dafcars.proboards.com/thread/3832/nos-parts

 

[Zelandeth]

6 hours ago, bobdisk said:

Always always be careful of nos parts. See my post on the Daf Owners forum:

https://dafcars.proboards.com/thread/3832/nos-parts

 

Aye, it's always a gamble.  I wound up binning probably 80% of the supposedly NOS parts I got with KPL because while they'd never been used, they looked to have been stored on the Titanic and were utterly wrecked. 

If changing these spheres required any serious work I'd definitely have ensured they were checked (I do know someone locally with a sphere tester) before fitting.  As it is, all I've lost is about 20 minutes so no huge hassle.

It is a gamble though, which on more expensive parts is one I'd be less willing to take.  Though it is one you kind of have to with an old Citroen these days given the laughable approach to legacy parts support from PSA...

[Zelandeth]

Well I don't know if it is the only one, but the oil pressure switch is definitely leaking.  This was cleaned up and completely dry before I set off today.

Will get a new one ordered from Prokschi later on.

Have to admit that I'm staggered at the difference changing the Dynastart belts has made.  Not so much in noise, but I'd say it's reduced mechanical vibration by about 80%, the engine just feels so much smoother now.  Wouldn't have expected such a small mass wobbling around a bit to make such a huge difference, but I know vibration can be strange like that once you take into account resonance effects and such.

It's definitely improved performance of the charging system too, it starts charging a good bit earlier than it used to.

The additional trim panels on the rear pillars has helped the overall feeling of refinement in the cabin I think.  It vastly reduces the amount of unfinished fibreglass you can see when you open the door.  The roof obviously being the major bugbear in that department now.

Trying to decide when I get to that stage whether to trim the panel behind the sun visor the same dark grey I've used elsewhere or to match it to the lighter shade I'll be using for the roof.

Thinking probably stick with the grey as that will nicely blend in with the windscreen pillars.

[bobdisk]

Spotted this,  @Zelandeth  any use to you?  

 

[Zelandeth]

5 hours ago, bobdisk said:

Spotted this,  @Zelandeth  any use to you?  

 

Thankfully the lights on mine seem okay as I remember.  Just the rubber boots from the back I'm missing. 

-- -- --

Nothing much to report from this weekend, though I did finally get around to giving the Jag a wash this afternoon.  The amount of gunk that was accumulated around the window seals and such like was frankly embarrassing. 

It's definitely one of the most awkward cars I've ever had to clean - especially the front and rear overhangs.  Doesn't scrub up too bad though from ten paces.

I hadn't spotted that the nearside exhaust tip had started to rotate on the tailpipe until after I took the photo...it's been straightened up again now.

Hoping to get the van in for an MOT this week to find out if there's any work needed for that I'm not currently aware of (expecting a shock absorber and a couple of brake pipes as the ferrules are rustier than I'd like).  Have had a couple of recommendations for a garage to use (my usual one can't deal with vehicles this large) so we'll see how that goes.

[Zelandeth]

Okay, I've got two portable split air conditioners to pick up later this week.  I reckon I might *just about* be able to fit them both in the Xantia with a bit of very careful Tetris being played.  If I can get the damned boot open.  That's what I'm going to go have a swear at in a minute.

If I had the van available however it would be a dead easy mission.

Following a few recommendations from the MK Modern Classics group on Facebook I've booked it in with MOTest in Newport Pagnell on Wednesday morning.

I've had a closer look at the brake flexible hoses and given the ferrules a bit of a clean up.  I'm not thrilled at the state of them and definitely reckon they'd be advised on.  I'll be changing them this year definitely either way.  I'm still irked they weren't even mentioned by the garage last year given the number of as far as I'm aware non existent faults they seemed to find on the brakes.

I've sorted the brake pad wear warning light issue - by disconnecting the sensor leads.  I'm not proud of it, but the problem is a simple fundamental issue with the system design which results in false triggering with modern brake pads.  Rather than the way for instance BMC did where they just have a light in series with a metal tab in the brake shoe, which grounds the circuit through the disc when the pad gets worn down, Mercedes have the switching done by a transistor - meaning that even the tiniest bit of leakage to ground at the brake end of things brings the light on.  I don't think I've ever actually seen one of these vans where the wiring wasn't snipped off decades ago... guessing this may be why!  I've not cut anything, no need to.  There are two connections that can be unplugged in the engine bay.  So if somewhere down the line I feel like modifying the system to be less hyper sensitive I can easily get it going again. 

Discovered the nearside indicator repeater was out.  This turned out to be a bit of poor design.  The ground for the repeater is via the mounting screw - however that's just a self tapping screw into a plastic plug on the inside of the wing.  A bit of rust on the screw where it passed through the wing = dead light.  I've done away with that and replaced it with a nut and bolt with a shakeproof washer, and a big blob of grease over it to keep water out.

Offside shock absorber looks like hell (the dust cover is held on with a cable tie), but works fine as far as I'm aware - again something I'd like to replace this year for peace of mind ideally.  At least being on leaf springs means that's less of a chore than with coilover setups.

There could be a thousand things I've missed though...it barely moved last year.  Obviously being an old Merc rust is the biggest fear!

[timolloyd]

Good luck! 

[Zelandeth]

Bloody French cars...

I've been unable to get that boot unlocked for well over a month now.  Right up till when I went to sort it today.

Of course at this point it immediately starts working absolutely perfectly and I can find no trace of any reason for the misbehaviour.

Business as normal then!

Then went and cleared about two tonnes of dead leaves and dog hair out of the interior of the van.

I'd really like to give the outside a clean too before the MOT, but am acutely aware that this is basically a whole afternoon of work in itself there!

[Fumbler]

9 minutes ago, Zelandeth said:

Of course at this point it immediately starts working absolutely perfectly and I can find no trace of any reason for the misbehaviour.

Business as normal then!

Ah. I feel your pain.

[Zelandeth]

16 hours ago, Fumbler said:

Ah. I feel your pain.

At least with the full expectation of it doing it again I've had the sense to remove the parcel shelf so I can get stuff in/out of the boot without dropping the seats if it sticks again.

I estimate that the lock will continue to work perfectly precisely up to the point at which I trust it to behave and put the shelf back in.  At which point it will again refuse to open.

[Zelandeth]

Had a few errands to run today, the weather was decent and as we weren't boxed in by school traffic for five minutes I took TPA out.

Another fifty or so miles done today without really thinking about it - even though I could have done without the monsoon that descended on the A5 about halfway home.  She handled it fine though and about 90% of the water stayed outside the car, reckon it'll be fine once I replace the window channel rubbers.

The windscreen is at least fully weatherproof now it seems so I don't wind up with water dripping on my knees any more - that used to get old in a hurry.

Dynastart belts are squeaking a bit just now at idle but I reckon they'll shut up once they've bedded in a bit.

[Zelandeth]

Well that could have been worse.

One sticky brake caliper (41% imbalance on the machine - though it felt like it was improving on the way home) and a couple of silly minor things that will take five minutes to sort.

I've got it booked in for next Tuesday to have the brakes sorted - though if I have the opportunity before then I may well whip the wheel off and see if it will respond to a clean up and grease of the caliper slides. 

Bit irked at the headlight aim...that was last touched by the previous test station and I always reckoned it was off since they fiddled with it.

[Zelandeth]

So let's deal with the simplest thing on that MOT fail list first.  Clogged windscreen washers.

Sorted.  This is a bit of an ongoing battle with the van as it had a lot of slime growing in the washer bottle when I got it and despite my best efforts there are still a fair few bits of gunk floating around in the system.  I'd quite like to convert this to have washers on the wiper arms though as they really struggle to get decent coverage across such a large and tall screen.

While I was outside I threw a bit of paint onto TPA's exhaust as the overspray on there from when I was messing about with the bodywork was bugging me.

Much better.

I then had to abandon the hopes of doing anything useful yesterday afternoon as I had to make a run over to pick up a couple of air conditioning units.  We *just about* survived last summer with the vented portables that we had, but they really aren't up to the job, and are horrifically inefficient.  I'd found a couple of portable splits for a good price, so went and grabbed them.  Much to the surprise of the seller, they both fitted into the back of the Xantia without any real effort.  The amount of stuff you can cram into the back of that car still surprises me sometimes - the deep dish of the rear windscreen really helps.  Cue brief distraction from car stuff...

Straight out the back of the car.

Looking a bit better after a thorough clean and de-stickering session.

Oh, and I set the clock on the programmer (that we'll never use) because it was driving me mad.

The window ledge hooks for the outdoor units are long-gone so I had to improvise something there - not difficult though.

I reckon this one dates from around 2000,

The little Serviso unit I reckon is probably early-mid 90s, and honestly seems a far more intelligently designed unit.

So, so much quieter than the vented units...Reckon we will be very, very glad to have these once the warmer weather arrives.  This house is very good at keeping heat in...great in the winter, but it really sucks in the summer!  These little portable splits are surprisingly hard to find these days - though given that when new they cost more than a conventional fixed split system A/C unit...not maybe that surprising!

Seriously considering picking up another two of the smaller ones and getting completely shot of our vented units in the summer...These are a bit more cumbersome, but the efficiency savings should make it worth it. 

[Zelandeth]

Bugger all done on any of the cars today.  In fact, aside from a five minute trip to Toolstation I've not even been near them today.

Turns out that the BBC want to do a brief segment (like a couple of minutes in one of their regional news shows) on the 40th anniversary of the Homeworld 81 Expo...And of course given that our house was built under contract to the then Money Programme, they want to get a bit of footage both from outside and looking into the house through a couple of the frontage windows.

This will be happening sometime over the next few weeks...Which means that a SERIOUS bit of tidying up needed to happen.  Especially in the Atrium which has been basically buried for the last year and a half.  With getting to the tip being a flying nightmare and charity shops not accepting donations, things have just slowly built up in there.

So today we started tidying it up.  Took all..bloody...day...but it's mostly done now.  Have had to recycle a lot of stuff we would normally have donated, but that's just how things have gone.  Xantia is full again so will be doing another tip run on Monday, and a huge amount of stuff has just been chucked into the shed...I'll curse myself for that next time I need to get the mower out.

This does mean however that for I think the first time in at least a year and a half, we can actually see the pool table again!

Once that pile of stuff at the far end is cleared enough you can bloody well bet it'll be getting used again.  Really do need to get the poor thing re-covered at some point though as the cloth is in really poor shape.  Well, cosmetically it is - it actually plays astonishingly well all things considered.  Just would be really nice to get it properly tidied up.

On the same note...I know we've got some graphical wizards on here...Before I waste hours and hours on it making a mediocre job of it...if I were to get proper dimensions of it, does anyone think they could reproduce the graphics in this for me?

The background should be black, text outline and the HGM logos white, and the Superleague text is infilled in a deep green.  I believe the 3D element of the text was a deep grey.  Is just something that my eye is drawn to every time I walk past it.  It's like having a car that's missing *one* wheel nut cover or something like that, it just bugs me!

[dozeydustman]

If the label is easy to peel off and scan, I can as my wife if she can produce a vector image which could be sent off to be professionally printed if you know the original colours. There is a professional print shop at the university where she works but unsure what media they can print onto. I can always ask if they do a plastic laminate

[busmansholiday]

On 4/21/2021 at 6:36 PM, Zelandeth said:

 

Have left them both wedged in place while the glue sets.  I'd really like to replace the windscreen demister duct, however it's still a way down the list - especially at £25+ a metre!

 

Decent aquatics shops do a plastic version of that tubing in various diameters from water overflow to filling the main water tank on motorhomes for considerably less than that. Guess how I know. 

[LightBulbFun]

10 hours ago, Zelandeth said:

Turns out that the BBC want to do a brief segment (like a couple of minutes in one of their regional news shows) on the 40th anniversary of the Homeworld 81 Expo...And of course given that our house was built under contract to the then Money Programme, they want to get a bit of footage both from outside and looking into the house through a couple of the frontage windows.

Oh I hope you manage to work TPA into one of the shots/in the background, bet that would throw some people for a loop! 

failing that, at least the Sinclair C5 since I think that matches the house very well, especially given there was an Electric Bedford CF parked out front when said house was new  

[Fumbler]

10 hours ago, Zelandeth said:

Small curiousity- why've you got two 7/6 inch fans in the atrium? Smoke extraction or something?

[Zelandeth]

1 hour ago, Fumbler said:

Small curiousity- why've you got two 7/6 inch fans in the atrium? Smoke extraction or something?

Using the atrium as a heat source - they're there (hooked up to a differential temperature controller) to pull warm air into the house if it's warmer out there than the thermostat set point inside the house proper.