Heater & Aircon Problems

[911addict]

I have a 1992 Turbo 3.3.

Not only is air not cold with aircon, but today I switched on hot air (without aircon) and the air was COOL through the side vents and driver side windscreen vent, and the passenger side windscreen vent and the center vents were slightly warm air (not hot).

I have already had some work done including replacing the cabin heater control unit (the whole box) and replaced receiver dryer and leaking expansion valve. Afterwards the aircon has been regassed but is clearly leaking, but wouldn't think this would affect the hot air.

Any ideas?

By the way, even when set at '0' my fan is constantly on and blowing slightly. My garage tells me this is normal and never stops completely. Is this true?

 

[Elliot Davies]

id make sure all the servo motors are all operational under the windscreen scuttle under the bonnet
these control hot / cold directions to the vents etc, thats assuming its the same as a non AC model
info on www.porsche964.co.uk although johns site doesnt appear to work at the mo, try it later
also lots of info on this subject on www.rennlist.com, i changed 1 off mine when i had different temps from the vents, price WAS £51 ea

easier to see these work if you have a person assist you

 

[Dave Wilkinson]

Mark,

The aircon and heating system in the 964 is quite complex (as I'm sure you now realise!!) and there are a number of servo motors and sensors which control the workings of it. Firstly, your use of the word "fan" leaves the description a little open to interpretation since there are many fans. In the turbo I believe there are two blower fans in the engine compartment (only 1 in the non-turbo cars), then there are the two booster fans behind the dash and there is a sampler fan on the back of the CCU.

The only fan which should run with the ignition on is the sampler fan on the back of the CCU. The rear blower fans should not run with the heat setting on the blue dot. Switch to a higher heat setting and the rear blowers should come on at slow speed. When moved off the blue dot the servos should allow the hot air from the heat exhangers to enter the cabin through the chosen vents (determined by the sliders on the CCU). The sampler fan allows the CCU to sample the cabin temperature and to control the hot air flow.

A quick check on the aircon can be done by engaging the aircon switch, turn the blower on full and check to see if the clutch on the compressor engages at any time. If there is insufficient pressure in the refrigerant there is a pressure switch up front near the evaporator which will prevent the compressor running and you won;t hear the "click" as te clutch engages.

I'd recommend a quick check of all the fuses - including the ones in the rear electrical panel - since this is a common problem with the rear blowers.

Servo failure is also quite common where the tracks on the PCB within the motor burn out and stop the motor.

Hope that helps.

Regards

Dave