Taxed the Ascot so I can run around in it to see if there's anything that still needs doing to finish it off and to see what packs up. Dina got in and realised she seemed to be sitting a bit high and it turns out that the passenger electric seat was stuck at the highest position at the rear and wouldn't go down. The front would go up and down but lowering it just succeeded in her sliding forward on the shiny cleaned leather. So spent the morning getting that working. Then turned my attention to a bit of testing on the HEVAC.

I've replaced one blend motor and given the other two a good clean out, check and re-grease and they are all working fine but..... It's been about 15 degrees so setting the temperature to 20 should result in hot air but it doesn't. To get hot air, the temperature has to be turned up to 26. If I poke the Program button the air comes out at maximum temperature so it isn't like the heater matrix is just cold, Nano shows it to be 65-70 degrees. Nano shows the two temperature motors to be giving a feedback figure of 83% when set at 20 degrees and rises as the temperature is turned up. Checked mine and got a figure of 70% when set at 20 degrees. Figured that the interior temperature sensor may be reading high so the HEVAC isn't giving hot air as it doesn't think it needs any but Nano shows that to be correct. Blasting the interior sensor with brake cleaner and the reported temperature dropped to -1 degree and the blend motors opened up and gave me hot air from the vents. But once the temperature sensor reported 10 degrees or higher, the output went cold again.

So it's doing everything it should, it's regulating the temperature it just needs to be told to keep the car hotter than it should. Both blowers are working, both pollen filters are new and a decent amount of air comes out of the vents, it's just the temperature is lower than it should be. I've even used the Nano to calibrate the blend motors and that made no difference. No book symbol on the display either. Any clues anyone?

Is the little aspirator fan grunged up and not spinning happily?

Dunno, that was going to be the next thing I checked but Nano shows it to be reading roughly the right temperature and it dropped rapidly when blasted with brake cleaner. So even if the fan is gunged up, I can't see it making that much difference. Mind you, one of the backlight bulbs has gone in the HEVAC so only half the buttons light up so it's got to come out anyway.

If you set the air to come from the footwell vents, is it warm then?

Nope, same temperature no matter what vent it's coming from.

So, been outside and done some testing. The Ascot and my ex-plod have both been parked since last night although the Ascot is possibly shaded from the weather a bit more than mine. To start with I checked mine before starting the engine, then started it, let it warm up and noted what it was doing. I then did exactly the same with the Ascot and it seems I owe OB another beer. The aspirator doesn't seem to be doing a lot. When I was doing the blend motors I noticed that the Ascot has the later HEVAC fitted in it so that probably explains the difference in blend motor positions as I suspect it has a different strategy. At no time did the fans speed up though and I suspect it was waiting for the aspirator temperature to start to rise before doing that.

Results are below

You'll notice that despite the Nano showing blend motor positions as a percentage, Mr Valeo has managed to achieve both 105% and 255%! But the difference in positions on mine does explain why I have to set the drivers side 1 degree higher than the passenger side to get air at the same temperature on both sides.

Top marks for the research/ report Gilbertd. You're now officially in the Analbean club :)
I've got pages and pages of spreadsheets doing back to back comparisons on various bits- never done the HEVAC though

I wonder if 255% is that it's wrapped around to -1% position?

Is it me or is that just confusing?

Probably but it made sense to me. On mine changing the temperature rocker altered the blend motors a bit at a time. Setting it at a fixed temperature and starting the engine caused it to raise the blend motor positions to get more warm air into the car quicker, as the temperature in the car came up, it wound them back to the position it thought was correct for the selected temperature.

On the Ascot, at anything other than LO, it whacks the blend motors to full heat right from the word go, presumably to speed up the heating when it's cold and then winds them back as the temperature comes up. As the aspirator isn't showing an increase in temperature in the car, it doesn't wind the fan speeds up but still winds the blend motors back so you don't get ridiculously hot air coming out as the heater core temperature rises. I'm assuming that's something that was changed in the firmware on the later HEVAC unit the same as it would no longer get offended if the compressor appeared open circuit like the early ones did if you added a relay without a big resistor.

gordonjcp wrote:

I wonder if 255% is that it's wrapped around to -1% position?

Probably, as it's using ordinary motors and gears rather than stepper motors, a bit of slop in the gears is going to allow the resistance from the pot to be lower (or higher depending on which way it's wired) than is expected. Same reason it shows over 100% at the other end of the travel. I suspect when brand new with no play in the blend motor gears or the cog on the end of the flap, it would read from 0 to 100%.

I put brand new blend motors in mine and they still go over 100% - I put it down to the general inaccuracy of the pots.

Without moderate airflow I can't see the aspirator temperature increasing. The fan speed increasing from a cold heater core/cold interior should be determined by the heater core warming up. I suppose it might back the blend motors off regardless a 15 degrees isn't that far off 21, giving a more gradual temperature rise once it actually has a usable source of heat.

Thinking about it... the blowers don't exactly get too lively in mine on a 15 degree day if I have it set to 21-22. I have a 2001 HEVAC in mine. I do also have a 96 one I could swap in to see if it behaves differently.

No 2 on the aspirator fan. Had similar with a SAAB 9000. Monster dust bunny in fan housing.

Clive