No Heat At All

[Victor]

Birds of a Feather - I purchased my 525i (M50) this summer, but was about to do coolant system work and decided I better test the heater first. I'll be darned if I can get any hot air out of anywhere at all.

I turned the driver's side control up (but just before the detent) and turned the passenger side all the way up too. I moved the center vent heat adjuster to full red. I opened the top dash vent and put the three sliders on fully open. No heat anywhere (at idle, temp gauge almost at 12:00).

Interestingly, while driving the other day I tried to admit ventilation air without turning on the A/C (which works great, but noisy ... probably the compressor). Warm air came in, when the blower was off. It seemed the only way to defeat it was to run the A/C.

I've read other threads about heater problems, but every other seems to have partial heat. I have none when the blower is on. Where do I start to diagnose this (or where do I find the heater control valve if I need to tap it to try and free it)? Thanks for your help!!

[genphreak]

Sounds like your problem is with the stepper motors in the HVAC unit. Easy to remove and fix- but u need to know which one/s. To do that, hook it up to a BMW diagnostics unit, it can tell you the ones that are not working properly, so long as you do not disconnect the battery shortly beforehand, as it stores the errors in volatile memory in the GM (IIRC). Don't try without doing this, there are a lot of stepper motors in the dash that are may take some time to get to.

[Victor]

Wouldn't the stepper motors be responsible for the rate of air flow depending on the setting selected by the control? In my case, those do work -- I get variable air flow depending on which detent I set the dial -- just no hot air (at idle... Going to test under load today). Thanks!

[Tiger]

I think it is your heater control valves... The pistons are stuck. Check the hoses and make sure they are all there... not disconnected or bypassed. No matter what speed the blower is, 185 degree coolant is super hot... you can't run out of hot air in the summer.

I suspect maybe your heater valves are bypassed. I got a used one if you need one.

Your experiment with hot air coming through without AC on is normal... all cars will do that in summer.

[Victor]

Thanks for the info. I think I may have jumped the gun, however, with my conclusion that there's no heat at all. I was at idle. Tested briefly while in motion, and air was pretty warm (not really hot, however) from the center controls. Need to try more when car is in motion. I'll report back. Thanks again!

[whiskychaser]

you can't run out of hot air in the summer.

Nicely put
You should also get hot air whether it is on idle or WOT. If you dont, you may not have enough flow through the heater matrix. Probably caused by clogged heater valves or (hopefully not) heater matrix. BUT what happens when you turn the driver's control up past the dent - do you get hot air then?

[Victor]

OK, ran engine at 1500 RPM's and fiddled with the controls. I'm getting warm air from center vents, windshield, and door vents. Not so sure about below the dash ... Engine temp just before 12:00 on the dial, ambient temp 85F. I would expect hotter, and it's mysterious why the driver's side below the dash doesn't seem particularly warm at all. I could use my digital thermometer on all ports, if it matters. With the only warmish air I could imagine being pretty unhappy in the winter.

In re-reading your reply, I noticed you asked what happens when I turn the driver's control up past the dent. I thought turning it all the way clockwise such that it goes into that final notch, defeated the driver's side control (giving complete control to the passenger side). I'm pretty sure this is what the owner's manual says, though I'll double check. I only turned it up to just before the max setting (for just this reason).

Assuming it didn't have to be turned up to max to make hot air, I think the key questions become:

1. Is my system working well enough to do a radiator flush (which requires heating settings)?

2. If I should be getting Hot air, not just sort-of-hot, is there anything relatively simple I could look into? (Don't want to pull everything apart).

3. I recently replaced my cabin filter. What a pain! Cursed the Germans through the whole job. But is it possible i didn't assemble something (albeit on the passenger side) which might compromise heat under the driver's dash area?

Thanks for your guidance!

Best,
Vic

[genphreak]

Check the auxillary coolant pump, under the hot water valves. It gets clogged a bit too. Can always hear it if its working, esp. if you place your ear on the end of a screwdriver and put that on it. If it is not running, the system's capacity to heat will be limited and heatflow will be very sporadic. Can't tell from your post but the heat controls are thermostatic and the other thing is that the hot water valves, when old may stick a bit (again providing delayed/sporadic heating) rather than locking closed or open for good.

But check your stepper motors, they commonly fail.

[genphreak]

No, stepper motors control the hot/cold flap/s feeding hot air to each of the zones.

[Victor]

Grand Master!

Your point that the heat controls are thermostatic is potentially very on-target. I tested the heat when it was 85 degrees, not thinking ambient temperature would matter! I'll have to test again when it's cooler.

How does one test stepper motors? If I understand it correctly, the temperature gauges vary the temp from A/C to heater continuously. So if I go from full A/C to full heat, should I hear the A/C compressor cut off and flaps closing?

Thanks,
Vic