And the winner is WallyP!

Fuse checked out OK, but the relay had an open circuit in the coil. So I replaced it, and everything works fine!

Thank you rennlist! In stead of tearing down half of the car, chasing the problem randomly, I fixed it in 10 minutes, I even had the correct relay laying around...


MM

 

do you happen to know which relay part number it is? just a standard one, or is there a special relay for the blower. I have the exact problem and i'm excited to get it fixed for the summer.

 

Relay part number is: 141 951 253 B (When you look in the fuse box, all of mine that are like this one have a big "53" stamped on the top of them.

Fuse Box slot "X" for the Fresh Air Blower and slot "VIII" for the Defrost.

There are several of the same relays so pull the negative battery terminal, swap slot "X" with slot "XII" (your horn relay), plug the negative back in and see if your problem is solved. If it works properly, order the fuse from one of the "big 3".

If it still doesn't work, disconnect the battery again and swap slot "X" with slot "VIII" and reconnect the battery to see if it's the defrost relay. This shouldn't have anything to do with it but you might as well try it before you start pulling out any hair. If it works, great, order the fuse. If it doesn't work then check and see if your horn still works before you spend time swapping everything back.

If it still doesn't work, you can now start pulling out hair.

Hope that's all it is!

 

I have a similar problem but it's doesn't fall exactly into any of Wally's three scenarios, sort of a combination of the 2nd and 3rd. My situation is DEFROST full speed, all other positions low speed for a while, then after 5 or 10 minutes FULL speed for the rest of the drive. Resistor pack? I'm afraid to ask what the resistor packs go for....

 

Defrost should be full speed all the time, that's normal. I'd start with swapping out relays with another working one in the fuse panel to see if it's an easy/cheap fix then go from there with the resistor pack.

 

Don said:
I have a similar problem but it's doesn't fall exactly into any of Wally's three scenarios, sort of a combination of the 2nd and 3rd. My situation is DEFROST full speed, all other positions low speed for a while, then after 5 or 10 minutes FULL speed for the rest of the drive. Resistor pack? I'm afraid to ask what the resistor packs go for....
__________________
A/C Blower Resistor 77-88 Main 928.618.101.01 $117.59

Porsche was concerned about the resistor pack overheating. It is installed in the HVAC plenum, where the incoming air will cool the resistors, but in addition, they put an overheat detection sensor in the pack. On the early car, if the resistor pack overheats - or if the sensor gets overly sensitive with age - the thermal switch closes, automatically popping the blower to full speed. This should increase air flow over the resistor pack, ending the overheat condition. In the later cars, the thermal switch opens, cutting off the power and thus the blower, ending the current draw to stop the overheating.

You can sometimes tweak the thermal switch to reduce the sensitivity. The most common cause for real overheating is dry blower bearings...

 

I have somewhat of the same problem, but checking the fuses and relays produced no results.

Here is what happens for me:

1. I get plenty of warm air when I put of the defog.
2. There seems to be a constant low heat coming from the dash and arm rests on any setting.
3. Moving the switch from defog to any other area causes the lighted "AC" button to turn off.
4. Fan switch does not change the fan speed.

Thoughts?

 

I did mine (87 S4 AT) today. I did not have any fan at all. Like a fuse or relay but both were good.

I found that when I changed the ***** on the control unit that the slider inside got loose !!

I removed the control unit from the console (takes no more than 5 minutes), removed the 5 screws on both side of the plastic covers and clip the slider under the ****.

Reinstalled and worked like new.

 

Here's a thread where the "always heat" issue was being hashed out. Several good suggestions. https://rennlist.com/forums/showthre...ferrerid=27688