Gjbacci

I am troubleshooting the AC system The forum threads have been a great help. Things I have done:

• Jumped R14 sockets 30 and 87 and the fan runs
• Jumped R14 sockets 30c and 87c and the fan runs
• A thread said to check voltage on terminal 85 and 86 to see if CCU is supplying control voltage. Not sure if that means check voltage across 85/86 or check both 85 and 86 to ground to measure voltage. I checked with AC on (car not running) and I saw no voltage across 85/86. When I checked 85 to ground and 86 to ground I saw 11 volts on each.

Its hard to hear the AC fan running when the engine is running (fister and sport cat). Should r the condenser fan run with the ignition on and AC on or does the pressure switch need to activate with the compressor running.

Thanks

Gjbacci

Forgot to add. I tested the relay and it was OK.

pp000830

Hi GJ,
What symptom has caused you to troubleshoot the AC system?
Andy

paranoidandroid

Check out this thread https://rennlist.com/forums/993-foru...diagnosis.html

To check CCU, 85 to GND and 86 should show +12V. Pressure switch will only engage the compressor between 37 and 390 PSI.

ToreB

The condenser fan shall start running on low speed as soon as you press either of the A/C switches. An external pressure switch activates full speed if needed.
The CCU relay output might be shot, but this is seldom seen.
This is an open-collector output, so it connects to GND when active. To test the output, leave the R14 relay in the socket and measure terminal 85C with a voltmeter. Instead of the relay, you can also connect a resistor between terminals 86 and 85C for the necessary pull-up load. With this load, terminal 85C shall be +12V when A/C is inactive, and be pulled to GND when active. If not, you could try to measure the output directly on the CCU harness connector to rule out any wiring fault. Look for pin K23, green/blue wire.
If the CCU output does not activate in any of these tests, it is most probably shot. This can be fixed.

Cheers,
Tore

Gjbacci

Thanks ToreB

are you saying the condenser fan should run on low with the ignition on, Ac switches on and the engine not running?

ToreB

This depends on CCU version, the early 964 CCU models were not as advanced on this point as the late 964 and 993 models. As for the 993, the CCU starts the condenser fan on low speed when the following conditions are met:
-Ignition on, engine started
-A/C engage wait time period expired (8-10 second pause after engine start)
-CCU fan speed setting above zero
-Outside temp sensor measures above 4°C
If the evap sensor also measures above 4°C the A/C compressor clutch is engaged.

There also mechanisms that allow A/C on if some of the above conditions are not met, as well as sensor fault override mechanisms.
This gives a small insight into how much development they put into these vehicles, also during production.
Cheers,
Tore

Gjbacci

Thanks to everyone for their responses. This will help me further chase down the issue.

Andy asked why I am chasing down so here is the whole story.

About 5 years ago I had the typical evaporator leak. I replaced evaporator and expansion valve (Griffith). Recharged system and all has been well. This vehicle is driven regularly for 6 months in the winter (Florida) and then sits for 6 months. On my return this year no AC. No compressor engaging. I put my gages on and pressure was too low to trip pressure switch. Obviously a leak somewhere. Jumped the R14 relay and added R134a. I can’t get pressures to spec. If the low pressure is between 10-17 @ 2000 rpm the high is too high. According to the excellent diagnosis write up on the forum this is possibly a clogged dryer. The dryer has never been serviced.

I am getting some marginal cooling but no where near specs. I know the heating mixing valves are operating since I rebuilt the little servo motors last year and with AC off and low temperature selected I am getting non heated ambient air.

My thoughts in adding Freon were to get my AC back and see if it held pressure. Probably screwed up by using R134a with some sealant as opposed to just pure refrigerant. If it didn’t hold pressure I would take to my service guy as I don’t have the equipment to evaporate and hold a vacuum.

So now it’s going to the service guy. Before it does I want to troubleshoot all I can to eliminate any other issues. Planning on having service

- evacuate all refrigerant and hold a vacuum. See if it leaks
- replace dryer as it’s accessible, not terribly expensive and never been serviced
-add r134a and oil by weight specs
-check pressures and performance

if the leak is not apparent (which I suspect since it’s currently holding pressure) add some UV dye.

if you think I am missing anything always interested in your excellent guidance.

thanks