I'm currently experiencing climate control problems with my 1991 C4 Cabriolet. The local Porsche dealership changed out two servos (defrost & mixing valve) that they said were bad. The climate control still does not function properly!! They said that the climate control unit was not sending signals to the the servos & it must be bad ($1260 list!!!!!!). They had 8 fault codes & now have 3!

I located a replacement CCU & plan on replacing it myself since I have no confidence in the dealership.

Do I need to erase the fault codes in order for the replacement CCU to function properly?

Thanks for your advice,
Pete

 

I don't think the codes need to be erased if the CCU or the problems are repaired. I only wish the process worked in reverse (just reset the codes, and the problems are fixed!). Definitely troubleshoot the cheaper stuff before replacing the CCU.

 

I found a working CCU out of a 1991 C2 for $220, shipped to my door. $1260 is outrageous!

My climate control symptoms are;
1) Constant hot heat from driver's side left vent.
2) Thermostat dial does not control heat but at the blue dot position the engine blower fan goes off & at other positions (near red dot), the blower fan works fine.
3) Slide controls do not work at all.
4) Fan dial (0 to 4) works fine.
5) Defrost button blasts air
6) A/C button light works (orange glow), but A/C compressor does not engage.

The local Porsche dealer changed the defrost & mixing chamber servo but still no luck!!!

Help!

Thanks,
Pete

 

The CCU faults need to be reset to have a reliably functioning climate control system.

The 964/993 CCUs are very reliable and rarely fail if ever. They only become
problematic when a strong battery charger is placed on a very low battery.
The CCU does have a typical problem of not fully turning off causing a battery
drain. This mode can result from an excessive battery charging voltage.

The most common 964/993 climate control system problems result from the
actuators, temperature sensors, and relays.