pantera928

My climate control fan in my 1988 S4 will not come on except in the defrost position where it comes on full blast. It used to come on in all positions at all the right speeds and then it started coming on only after it had been turned on for a few minutes. The resister pack checks out but I get no voltage to the fan except in defrost position. Any ideas? I tried looking for old posts on this subject but got frustrated. THanks

MainePorsche

Does your AC compressor engage when you turn it on (not in the Defrost mode) ?
Visual confirmation.

pantera928

I do not know for sure. I was just trying it mostly in the various vent modes. I did not push the AC button.

MainePorsche

Visually confirm the compressor starts spinning.
Not just by hearing flaps open/close, or fans turning on from inside the car.
This is important to confirm, and move forward with.
Not in Defrost mode.

pantera928

AC button lights up and the compressor comes on only in defrost mode

MainePorsche

Your Relay X, the Air Blower Relay is not functioning. Needs to be replaced. If you want to try, you can pull it and jump its function as confirmation by bridging the 30 and 87 pins. This will give you blower control and allow your compressor to engage by giving it current.

The power to operate the A/C compressor clutch comes thru fuse #17 to Relay X, the blower relay. If the A/C blower works, the fuse and this relay are good - if the blower doesn't work, neither will the compressor.

From the relay, power goes to the A/C switch on the dash.

From the A/C switch, power goes to the A/C control head. There is a small relay in the control head that controls the power to the compressor clutch - this relay can fail.

The power then goes to the antifreeze switch on the A/C evaporator. If the evaporator gets below freezing, the switch opens, cutting off the compressor.

From the freeze switch, power goes back to the central power panel, and goes to both the supressor in Position XI and out to the low pressure switch on the A/C receiver/dryer forward of the radiator. From there, power goes to the ccompressor clutch.

pantera928

Thanks
I will check it tomorrow and let you know.

MainePorsche

Have a Good Night Greg.
Happy Hunting.
Craig

Alan

Assuming the blower doesn't run in (max) 4 switch position - this is not a blower resistor issue - this position should work even with the blower resistor pack removed...

First check that the connector has not fallen off the HVAC head unit blower switch...

Check the head unit connector also...

Swap the Fresh Air Blower Relay (X) for a working relay (use the horn relay if it works).

If that doesn't work...

Also try swapping Relay (IV) for a working relay (also can use the horn relay).

Alan

pantera928

Craig
Okay, X marks the spot and I was too lazy to figure it out on may own. As soon as I wiggled that relay it started and stopped the fan and compressor. Since I always keep several new ones, I replaced it with a new one that does not stop and start things when I wiggle it. Thanks so much for your help and patience. Where in Az are you? I may be out that way on business sometime soon.
Cheers
Greg

MainePorsche

Good to hear.
Could sound like your CE Board may need a little tending to.
Alan, the Electron Master, is in AZ. I'm way up in the other corner in ME.

pantera928

Not sure what a CE board is. If it is the fuse/relay board, I had it out a couple of years ago due to a windshield leak that cooked my jetronic. THe original bedding for the 928 windshields dries up over time and you can just about push the windshield out. Had it happen before but on a CIS car so issues were different.

MainePorsche

Central Electrics Board. I even capitalize the 'B' in Board to pay homage to this entity.
Things shouldn't wiggle on it. Clean and inspect all the fuse and relay contacts. Fix what you need to.
REMOVE THE BATTERY GROUND STRAP IN THE REAR BEFORE PLAYING THERE.

pantera928

As I said, I had it out a couple of years ago. Sounds like I missed a couple of items like the "X" relay. looks like iI may pull it again. Thanks

prmonahan

Similar problem on my '82 928 USA 5-sp. I followed Wallys troubleshooting at https://www.928gt.com/t-wallyhvac.aspx.
- Blower doesn't work in any position (0 through 4) nor when set to defrost;
- I applied 12v to the blower motor at the connecter coming from the resistance group, and it DOES turn (so it's not the blower motor).
- replaced fuze #17 (fresh air blower)
- replaced both relays XXI (blower) and XXII (defroster). I even tried a jumper across pins 30 and 87 in the Relay XXI socket, just to be sure. - still no blower.

Is this indicative of a bad resistance group (in the plenum under the windshield wiper cowling), or a bad HVAC control head? Any additional troubleshooting suggestions appreciated. I have not yet broken out the multimeter to check voltage on each pin of the resistance group connector at different fan settings.