Deserion

My apologies in advance, I have been searching the topic relentlessly and think I have a solution, but wanted to run this by everyone else to make sure I'm on the right track.

Intermittent compressor engagement when A/C button(s) depressed
Directional sliders do not redirect
Fan speed **** inop (one speed)
Fan speed shuts down when temp. turned up from full-cold
Defroster doesn't seem to do anything

Now it seems that the CCU needs to rebuilt. No problem. But what else should we check before plunking down the cash on a rebuild? Some of the threads were mentioning fuses in the rear panel for the rear blower that seemed to solve the issue, some of a fan relay.

Thanks for your help, everyone!

altarchsa

Try these:

http://www.porsche964.co.uk/technical/servos.htm

https://rennlist.com/forums/964-foru...ns-issues.html

tbennett017

It could be the CCU, but it could also be a bunch of unrelated issues. I have had to deal with all of these independently.

AC and Defrost could be affected by low gas pressure
The Servos poop out at this age, and need attention/replacement
Fan speed could be a ballast resistor

+1 on the threads above first...

reed

The 911 climate control system has been a Rube Goldberg setup almost from the beginning. With the advent of electronic controls in the 964, this system got even more complex.

It is very difficult to diagnose problems since there are so many interrelated systems. When I bought my car I was getting warm air in the cool settings. I checked all the usual suspects only to finally figure out that the servos were simply misadjusted. A simple fix that took days to diagnose.

Rocket Rob

Do you have access to a Hammer or Scantool? That can be very helpful in diagnosing this. I especially like how you can command each CCU function separately (ie rear fan low vs rear fan high).

tbennett017

http://www.obd1interface.com

Deserion

Thanks for the replies. Would a Durametric also work for this process? It would also work for my Boxster so that would be better than a single-car tool.

I'll get to cracking on the car this evening to see what the results are.

Deserion

Looks like the rear blower motor fuse was blown. Replaced that, the compartment fan now runs (and the oil temps. are a little cooler compared to yesterday).

Also, I had both the large and small snowflake buttons pressed before. With just the small snowflake on now (had tried this last night to no result), the directional sliders work, the fan speed **** works, the fan does not cut off when the temp. is adjusted (though still does not get hot). However, the compressor still kicks on/off intermittently.

Going to pull the CCU this weekend and see if the sampling fan is bad. Will likely send it off to be repaired.

Vandit

When I took my car in to a shop because the a/c wasn't blowing cold (needed a recharge), they also did a bit of a review of the HVAC system functionality. They told me that my rear heater fan was not working and had been disconnected, thus, the HVAC system won't work on any temp except Max Cold. Since i'm in Texas, and it's currently Summer, I never turn it up from Max Cold, so for the moment, I don't care, so I haven't addressed it.

It's interesting you say the oil temp runs cooler now that you fixed the heater fan in the engine compartment.

Can anyone else provide feedback on this? Will a non-functional rear heater fan really cause the engine's operating temperature to be higher? What happens if I ditch the whole unit for a blockoff plate such as the one sold by Rennline?

reed

By design, the rear blower also operates independent of the HVAC system. When operating temperatures are high, the blower kicks in and draws hot air from the engine. I assume it then dumps the hot air out a bypass.

When I replaced a noisy blower motor this past weekend, I noticed lower oil temperatures as well.

tbennett017

Yes, it draws hot air out of the engine compartment. Check out the large air pipe nearthe primary muffler location. The air gets dumped out near the rear wheels OR is used to heat the cabin.