Constant heat in the footwell
Constant heat in the footwell
I'm pretty sure I saw something about this recently but I didn't bookmark it and now can't find it. There is a constant flow of hot air in the footwells (535i). If I open the vent down there it's like I have the heat on MAX but even with the vent in the "closed" position it still gets really hot in both footwells. I'm not sure if it's a related or separate issue, but the AC works great in low gears while accelerating but at highway speeds the temp is nowhere near as cold. There's more heat coming from the footwell at this speed so it compounds the problem. Any ideas?
Make sure all the body plugs are in place. Especially if your car is an automatic, as the plug for the clutch master seems to fall out and will let in plenty of hot air from the engine compartment. There are some other holes to check, too.
Besides that issue, your heater control valve might be shot. When it goes bad, the fail mode is to full heat, but not usually at speed. Another related problem to this one is a bad interior temperature sensor on the lower dash trim, above the pedal cluster. If this unit is unplugged or malfunctioning, the car will default to full heat when the temperature dial is not set on maximum cool. You probably do not have this set on anything other than the coldest temperature in TX, though. But to check if your car is adding heat, open up the top and bottom air distribution sliders all the way to the right (put the middle one all the way left) and feel for any hot air with the A/C turned off once your car's coolant is warm. If you get hot air blowing that is variable upon the fan speed, then the problem is because the car is adding heat.
The other thing I can think of if you get heat only at speed is an issue with the fresh air flaps not closing or sealing properly. Also, if your car is a pre-'86 build, ALL the HVAC levers must be to the left for maximum cooling--- the middle one does not need to be open. Otherwise, you will let in hot, outside air that typically comes in via the foot well vents even when closed. Now, if your car is a '86 and later production with the servo controlled fresh air vent, make sure it is in place and working. The screws tend to fall out and this won't allow complete closing of the flap. On the later cars, the servo system was added because people would forget to leave the middle lever open and then complain about the A/C output.
Besides that issue, your heater control valve might be shot. When it goes bad, the fail mode is to full heat, but not usually at speed. Another related problem to this one is a bad interior temperature sensor on the lower dash trim, above the pedal cluster. If this unit is unplugged or malfunctioning, the car will default to full heat when the temperature dial is not set on maximum cool. You probably do not have this set on anything other than the coldest temperature in TX, though. But to check if your car is adding heat, open up the top and bottom air distribution sliders all the way to the right (put the middle one all the way left) and feel for any hot air with the A/C turned off once your car's coolant is warm. If you get hot air blowing that is variable upon the fan speed, then the problem is because the car is adding heat.
The other thing I can think of if you get heat only at speed is an issue with the fresh air flaps not closing or sealing properly. Also, if your car is a pre-'86 build, ALL the HVAC levers must be to the left for maximum cooling--- the middle one does not need to be open. Otherwise, you will let in hot, outside air that typically comes in via the foot well vents even when closed. Now, if your car is a '86 and later production with the servo controlled fresh air vent, make sure it is in place and working. The screws tend to fall out and this won't allow complete closing of the flap. On the later cars, the servo system was added because people would forget to leave the middle lever open and then complain about the A/C output.
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Kerrvillian
- Posts: 97
- Joined: May 22, 2023 7:17 PM
- Location: Texas Hill Country
Re:
Old post, but this helped me a lot. Just fixed the A/C in my '85 524TD and had some serious heat coming in the footwell and through the dash at road speed. Searched Google and this thread comes up. Dropped the lower dash cover and sure enough, that plug had fallen out. Refitted it and added some tinfoil tape and solved that problem.Justin_FL wrote: Jun 27, 2009 7:54 AM Make sure all the body plugs are in place. Especially if your car is an automatic, as the plug for the clutch master seems to fall out and will let in plenty of hot air from the engine compartment. There are some other holes to check, too.
The other thing I can think of if you get heat only at speed is an issue with the fresh air flaps not closing or sealing properly. Also, if your car is a pre-'86 build, ALL the HVAC levers must be to the left for maximum cooling--- the middle one does not need to be open. Otherwise, you will let in hot, outside air that typically comes in via the foot well vents even when closed.
Also learned something. Did NOT realize that leaving the center vent lever open would let in outside air! Explains why I couldn't pull below 52˚ yesterday! I've only worked on 86 and later E28's with the automatic fresh air flap.