Final Stage Resistor -> No Heat
 

Hi,
does anyone know if a failing Final Stage Resistor will (or could) have any effect on the temperature being pushed into the cabin? Or does it ONLY affect fan speed?
Thanks

I believe only fan speed.

Heat might be thermostat, heater valve, clogged heater core, temp sensor in hvac system, or the hvac control itself. Possibly air in the system if it’s been opened up.

Any maintenance history? I recently had a new water pump that had the impeller installed backwards from the manufacturer. Got little flow to the heater core causing my issue.

2005 X5 4.4L - Has new thermostat, auxiliary water pump is working (although when I put the test light on it - it gets power for 4 seconds and then no power for 20 seconds then repeats cycle) (Also have access to a 2001 X5 3L that does the same thing) Blower fan works fine.
Once at 12 o'clock operating temperature, when at idle, the blower blows cool air only. If I rev it above 1500 rpm I get hot air. Seems that if I put blower speed to half power I get hotter air than if I have it at full speed.:fencing:

That could happen if your thermostat is stuck open. Did you replace it when you did the water pump?

Not sure when the water pump was done but thermostat was done a month ago. Truck was chilly before new thermostat. That's why I did the thermostat job because I heard that they fail open and I figured it was keeping the truck cold. New thermostat, no difference. Operating temperature was always at 12 o'clock position.
Thanks for any help you can give.

Sorry, I just read your post again and noticed you already said you had replaced it. My bad. Did you use genuine BMW t-stat? The cheap ones can fail prematurely. Just giving you ideas. What kind of condition is your cabin air filter and ducting in? Have you checked them recently?

Thermostat is Wahler OEM.
Didn't check ducts or cabin air filter.
But I am experimenting with Heater Core Sensor. Will keep you updated.
If you get a chance and have an E53 close by, throw a test light on the auxiliary water pump blue wire please. While having the heater/blower on check to see if yours also gives 4 seconds of power and then 20 seconds of no power. I am inclined to believe that this may either be my problem or at least a part of it.
Thanks for your help.

Another way to troubleshoot the heater valve is by unplugging it. Unplugging makes it default to the open position. If heat works then it could be related to the temp sensor in the hvac duct. If still no heat might be faulty heater valve.

I know it might seem like a lot of work but might be worthwhile to inspect the water pump. Maybe the impeller is damaged? While your at it try to reverse flush the heater core.

Good luck, I know it’s frustrating but it is probably something simple.