byrdman454

I just tore my interior out and replaced the defrost, center comb, and recirculation actuators. The footwell actuator already help vacuum. When I checked the heater valve vacuum 2 weeks ago, it was fine. Now since I have it all back together, I am only getting hot air coming out. What is the deal? Could I have messed something up when replacing the actuators, or is it a coicidence that possibly the heater valve is now losing vacuum? What are the other causes of hot air all the time?
Thanks

John Pirtle

Maybe your a/c button isn't plugged in?

There's a write-up on my website describing how to use a vac pump to check the actuators, etc.

It's sort of mind-boggling at first but you actually can diagnose these issues!!!

John Pirtle
87 a/t 166k
http://members.rennlist.com/pirtle

Ispeed

Bad heater control valve? It's a $14 part, I just replaced mine. Warm air and not much better with a/c on, now is cool and cold with a/c. If it's old, just replace it.

byrdman454

John...I read your writeup and did the test. That is how I found out the 3 actuators were out in the first place. The A/C was working fine except the flow would come from everywhere since the actuators were not working. I do not know.

The heater valve is not that old...maybe a year or so. Like I said it checked out fine when I did the vacuum test two weeks ago. If this is what is wrong, no problem, I will check it tomorrow. I just want to be sure there is not something else that could be causing my hot condition since I just got done replacing all that stuff.

Thanks

byrdman454

By the way, it is not an A/C thing. Just running the blower without A/C on full cold is air that is HOT. When I push the A/C button it cools it doen to luke warm. Any more ideas???

Thanks

okbarnett

make sure; the clutch/compressor is coming on, the heater/water valve closes when the system comes on, all the other valves function correctly when you slide bar from symbol to symbol.

John Pirtle

Check the mixer flaps. Look on my service page under a/c. At the bottom is a section on the temperature mixer flaps. Make sure the motor is moving the arm etc up and down, and check the connecting arms by the glove box.

You might also check into the temp sensors but even if they are bad the mixer motor should still move when the temp slide control is moved to the extremes.

Now, when you stop a 928 it's common that the heater valve will lose vacuum, open, and allow hot water to the heater core. When you restart the car you will get pretty warm air until the core is cooled back down. If you have the a/c on, the a/c will be not-very-cold while it cools the core off. If it still feels like HEAT after 10 minutes of freeway speeds, then you definitely have a problem. HEAT comes from the heater valve being open and the mixer flaps bringing air through the hot core.

Check the heater valve, mixer flaps and motor, and a/c freon charge. I hope it's the cheapest!

John Pirtle
87 a/t 166k
http://members.rennlist.com/pirtle

FeedNfrenZ

Check to make sure that the incoming vacuum line to the A/C control switch didn't pop loose. Drives side of center console. I think it's the white vacuum line?

Nicole

Usually, "Hot Air" is a sign that you might have added a used car salesman to your system....

Just kidding!

Best of luck in figuring out the real cause for this!

mpesik

Where did you buy that part from? Thanx.

Garth S

John has far more expertise in these systems, so if you have followed all of his tips, here's a couple more pragmatic things to verify: remove the air box, and with engine warm and running, cycle the temp control slider with AC off - and verify that the arm on the hot water control equally cycles. If not, you know where to look - if it does cycle correctly, then the temp sensor or its wiring may be suspect: the temp sensor is located in theinlet end of the flex hose providing cooling air to the alternator- behind the left front fender wheelwell cover.. all independant of your AC system, which seems to be working fine.
Mpesik - re the heater control valve, there was a thread giving the Audi p/n for an all metal sealed replacement - that is the direction I would head if a replacement were req'd. I saved the reference ... somewhere ....

byrdman454

UPDATE:
I pulled off the drivers side console cover and checked the vacuum line manifold. Sure enough, the black feed line had come disconnected. No wonder I was having problems. It must have accidentally come undone when testing the rest of the lines. Everything works like a charm now. Thanks for all the feedback on my post!

FeedNfrenZ

Woohoo! I got one right! okay........... I was wrong about the color!

John Pirtle

I have been told that this all metal heater control valve works -
a Belkamp with a NAPA part number of BK6601410

The valve need 3/4" fittings on both ends to fit our 928 hoses. And should default (no vacuum) to an open position.

I'm using a NAPA valve (don't know the part #, sorry) that is hard plastic but has a metal valve. Been working fine for 2 years.

mpesik

Thank-you Garth S. Mike