Carpokes Porsche Forum

Hi all,

I am having issues with my AC in m '87 turbo.

I recently replaced the compressor on the car (less than 1,000 miles ago). The car then went to the shop for about 6 months. When I got the car back up and running, the AC blew cold for the first few days before I had an intermittent heating issue. I'd get 15 seconds of cold, and 15 seconds of heater air. Long story short, I had a bad exterior temp sensor. I was able to diagnose the issue using Tom's wiring diagram and found that the outside temp sensor was reading well out of spec. So, replaced the sensor with a new thermistor and all was well. Cold AC again.

I just came back to the car today after not touching it for a few weeks, now I get no AC air. Just what I believe is ambient air. I am in Texas so the ambient air is around 100 and the air blowing through the vents is around 110. I'm assuming that's just ambient air, and not heater air.

I just checked to see if any of my CCU parameters were out of spec using Tom's diagram again. Nothing is out of the ordinary, besides the mix temp flap controller, which reads 2,550 ohms.

My CCU unit lights up as usual, and when I hit the frost button, the light turns on. I can hear the compressor clutch engaging, and the car idles up accordingly. When I turn the AC on, and set the temp to the lowest setting, the air does not blow cold. When I turn the heat on the dial all the way up, the air does not blow any hotter. No matter what I do, it blows the same temperature.

With all the issues I've had with it, I am almost ready to hand it over to someone who knows what they're doing, but I'm giving it one last go before giving up on it. Any help is much appreciated!

Solved my issue. I should've started at the basics. Checked the plastic clip... that was my issue! Tom, thank you so much for putting together .stls for so many of the little plastic bits on this car! You just saved me downtime and granted me some much-loved instant gratification!

TurboD wrote: Fri Jun 30, 2023 4:16 pm Solved my issue. I should've started at the basics. Checked the plastic clip... that was my issue! Tom, thank you so much for putting together .stls for so many of the little plastic bits on this car! You just saved me downtime and granted me some much-loved instant gratification!

That's great to hear!! How did your printed clip come out?

Tom wrote: Fri Jun 30, 2023 4:19 pm

TurboD wrote: Fri Jun 30, 2023 4:16 pm Solved my issue. I should've started at the basics. Checked the plastic clip... that was my issue! Tom, thank you so much for putting together .stls for so many of the little plastic bits on this car! You just saved me downtime and granted me some much-loved instant gratification!

That's great to hear!! How did your printed clip come out?

The print came out great. Had a couple re-prints but found that CF Nylon worked well. However, I don't think the clip is my issue after all. I might've broken it in the process of removing the kickplate cover, because it was definitely broken when I got to it, but the issue persists.

After installing the new clip, I turned the car on, and no AC. I stuck my head under the driver's footwell to take a look and see if the servo was actuating. While turning the temp dial to max heat, waited 10 seconds, the servo arm did not move. Then I turned it to full cold, waited 10 seconds, and still no movement from the servo arm.

This is the position it's stuck in. Any ideas on what to do next?

Have you tried manually powering the servo (like I do in the video)? That's probably the first thing I'd do just to make sure the servo isn't dead. If that checks out and the system passes all the other tests on my charts, and assuming the heater valve under the hood is ok, then I'd probably open up the climate control unit and look for obvious issues. That unit has 3 pcb boards connected together with rows of small metal wires. Those wires can corrode and basically turn to powder. Chips can burn out too, so no guarantees it will be something that easy. Let me know what you find and we'll try to get it going again. (In the meantime, if you just need the heat off, see my video on how the flap works, and you can just take the clip off and zip tie the level to the no-heat position.)

Tom wrote: Sat Jul 01, 2023 7:30 am Have you tried manually powering the servo (like I do in the video)? That's probably the first thing I'd do just to make sure the servo isn't dead. If that checks out and the system passes all the other tests on my charts, and assuming the heater valve under the hood is ok, then I'd probably open up the climate control unit and look for obvious issues. That unit has 3 pcb boards connected together with rows of small metal wires. Those wires can corrode and basically turn to powder. Chips can burn out too, so no guarantees it will be something that easy. Let me know what you find and we'll try to get it going again. (In the meantime, if you just need the heat off, see my video on how the flap works, and you can just take the clip off and zip tie the level to the no-heat position.)

Just tested the heater control flap by hooking it up to power as you did in the video. I heard it work and verified that it moved positions. Here is the after picture.



I took apart the CCU. Managed to not crack the clear plate—so I guess that's a plus. I didn't see anything immediately wrong with it, but I am not sure how to take the unit apart further as I don't want to break it. Any thoughts on what to do next?

Hmmm, then the cc unit is not moving the servo for some reason. Did you check the servo position sensor resistance too? If that's ok, and if all the temp sensors are ok, then it's pointing toward a bad cc unit. What year is that cc unit from? It looks different than all the ones I've seen!?!

Tom wrote: Sat Jul 01, 2023 2:27 pm Hmmm, then the cc unit is not moving the servo for some reason. Did you check the servo position sensor resistance too? If that's ok, and if all the temp sensors are ok, then it's pointing toward a bad cc unit. What year is that cc unit from? It looks different than all the ones I've seen!?!

Before I removed the CCU unit this latest time, the flap position sensor was reading 2550 ohms. Now, it reads 2150 ohms on one end and 130-140 ohms on the other.

The car is an 87. I'm not sure the CCU give a year on it. The part number is 944 653 021-04.

I just tested the system with the flap open and the flap closed. Hooked up the CCU, turned the AC on, max cool temperature. Disconnected the clip, manually pulled on the rod, and waited 20 seconds. Air was 100 degrees. The I pushed the rod up, waited 20 seconds, and the air was still 100 degrees.

Did you check the defrost flaps too, and the heater valve under the hood? Sure your AC works?