I've been going crazy with a non-functioning heater blower, when I suddenly thought of something. Ithink I remember seeing somewhere(like in the owner's manual possibly) that my car (99 a4 2.8Q) has a Heat/AC system that is designed to operate only after the car has reached normal temperature. In my case, I believe either my temp. sensor/sending unit and/or temp. gauge are kaputt, because the needle always stays pegged on cold no matter how hot the car gets.

Could this malfunctioning temp. sensor/sender/gague be causing a false reading that is preventing my heater from working?? has anyone ever heard of anything like this? Please help me, wise Jedi/Audi Council.....

 

Wise Jedi/Audi Council... thats a new one. LOL

Yeah most likely your coolant temp sensor and/or your thermostat is stuck.

Josh

 

I didn't just imagine that bit about the system not working when the car is cold right? I mean, the heat has been broken as long as I've owned the car, so I've never been able to check if it was really true or not. Does yours do this?

 

Well my car doesn't put out any air or hot air until it warms up just because there is no hot coolant running through the heater core yet. So if your thermostat is stuck then you won't be getting any hot coolant in there (or at least I don't think you will be). Does your fan work at all?

Josh

 

nope. But the screen(heater controls LCD) shows the fan cycling on and off every ten seconds or so. and yet the fan does work(I've tested it with a known power source directly at the plug terminals). But you say your fan works even when the car is cold(oviously not blowing hot air though), so this doesn't look like it could be my root cause then. hmmm.....

ANYTHING TO KEEP FROM REPLACING THE MAIN HEATER CONTROL UNIT!!!! baah!

 

Manually increase the fan speed with the A/C on.
Does the fan work?

 

my heat worked fine when my coolant temp sensor needed replacing. so it's definitely something more than your coolant temp sensor.. although it could also be your coolant temp sensor.

 

Sounds Like your thermostat is stuck. Had the same issue on a different car, car kept over heating though and it was a GM! I think audi's are a little more on the back-up side, andlet the coolant flow through but not turn on the AC system or heating system. If your gauge is not reading an operating temp than it kind of narrows it down IMO! Its either the gauge itself, or the sensor/thermostatthat opens up and lets the hot coolant flow through. So since your heating doesent work I think it narrows it down to the sensor/ thermostat. IMO! You might need to replace or add more coolant after you replace the thermostat, depending on its location! You can also take it to a local shop and get a pressure test done for your coolant system. Or check if the hosing into the radiator is stiff and warm after you run the car for a while and if the return excess hose (located by the overflow tank) is kind of flabby and soft.And try to re-rout this pressure loss in between the sensor/thermostat on either side. you can narrow it down that way!

 

I know there is something awry with the temp sensor/sender because it looks all pink and crusty(the one on the radiator lower hose: passenger side, just behind the radiator and in front of the engine). I read both tech threads on the temp sensor/flange, and i know it's worth my while to replace this sensor.

I'm curious though, about the thread that discusses the temp flange(read of the engine, between block and firewall, not fun to get to), because I'm not clear what that's all about. The pictures made it look like it was the thermostat housing(which i understand from my other cars) but i don't see why there are wired sensors at TWO points in the cooling system(#1- the lower hose on the front pass. side ; #2-this "flange" behind the engine).

Does the A4 have two temp sensors/senders, or do they serve different functions? And which would be more advantageous for me to replace/repair?