tbennett017

... and before you refer me here:

https://rennlist.com/forums/964-foru...-it-there.html

(Thanks Babalouie)

I did replace the fan resistor today based on this process. The old one reads the same resistance as the new one that went in, so it wasn't broken. The one I pulled out shows an '05 date on it... so its not original to the car.

So now with the new resistor, what happens is while the AC is set to full cold, the compressor runs only part of the time, and the condensor fan cycles as above. It's not warm outside, (~45-50 Deg F) so is this part of the issue? All the rest of the system (mostly) is new. New compressor, and evaporator.

Thoughts? Or should I wait til it warms up? Is there too much pressure in the system? What is normal?

DWS964

It could be the high-pressure switch which will cycle the compressor off if the system pressure is too high. I had an over-pressure situation on my other 964 a while back. I am unsure, however, if that will cause the condenser fan to cycle on/off.
Is your condenser fan cycling in Low speed or High speed? When the resistor is bad, the fan cycles in the High speed. (I believe).

tbennett017

AFAIK it's at the High setting. on/off

Still wondering if the ambient temp has any effect? Not too sharp on Boyle's law and all that.

ToreB

There's no ambient(outside) air temp sensor for the HVAC system in the 964, this was introduced in late '95 993's. I would guess the high pressure switch that does this to you, it can easily be checked with an ohmmeter. The CCU is also involved in switching on the condensor high speed, but I would start with the pressure switch. Details where it is and how it's wired are given here:
www.porschehvac.bergvill.com

I have also seen this cycling behaviour in 964's fitted with a 993 CCU. That needs some changes to the wiring, depending on CCU model used.

Cheers,
Tore

tbennett017

Thanks Tore,

I jumpered the relay connections and the fans run at low speed. Strangely enough, when I installed a new resistor on the oil cooler side, the AC side fan now runs normally... Not sure how that works, but the oil cooler side resistor looked pretty bad, but it did measure out the the same resistance as the new one.

Weird. Now that the resistors are new, the fans work normally, but the AC compressor does kick on and off... Normal? I dont' recall this happening in the past, but maybe I never noticed.

I measured at the pressure switch based on your page, but the wire colors are different. But it tests out okay.

Maybe this is normal?

ToreB

I've never before seen any dependencies between the oil cooler and the condenser fans. However, if a 993 CCU is used in a 964 there may arise issues due to different wiring schemes.
My compressor cycles every now and then, so I would think this is normal behaviour. I have checked that the cabin air vent temperature is within the specifications when the A/C is operating.
Cheers,
Tore