The Phantom

Hello,
First post, please be nice.
I have an 84S manual, Australian delivered.
The aircon works when I first drive out of the garage, then after 20mins or so I notice the car heating up, and find that the interior fan is no longer working and neither is the aircon pump. I can get the AC pump and interior fan to work by sliding the lower slider all the way to the right in "Demist" mode. Fuses all ok. I even changed the heater control unit because I thought that must have been the problem but it still has the same symptom so that appears not to be the issue. I know I have vacuum leaks because in hot weather under full throttle the aircon changes from the face vents to frozen feet mode.

Any ideas?

Peter

jpitman2

Is the AC the auto type? If so the temp sensor in the alternator cooling hose may be an issue - the connector near the inner guard/fender can be corroded and fail to send correct signal. Since so much of the AC depends on vacuum, suggest you fix that first then dbug this problem, if still there. Also the relay on the AC control board is badly overloaded driving the AC compressor clutch, and may be failing.....the fix is to install a separate full size relay out near the compressor, inserted into the std clutch feed line. Is the slide control in good order ? Maybe its contacts need cleaning ? Do you know if the AC gas pressures are OK - they may be going high or low, and turning off the compressor?
jp 83 Euro S AT 57k

FredR

The primary suspect when the a/c suddenly stops after a brief period of operating OK is invariably the control unit relay build into the front panel assembly. The stock relay is considered marginal at best and eventually they get tired
You can use the defective relay to act as a relay for an auxiliary power supply directly to the clutch via a separately fused power supply taken from the hot post but as JP says relay replacement is the correct approach. A new relay can be soldered in or a higher rated relay [5 amps minimum?] installed piggy back as it were. There is an excellent write up for this by Dwayne [ search 928 Dwayne's garage in Google].

Other things may be causing your condition but I would say it is a 99% certainty it will be the relay- they all go sooner or later.

The Forgotten On

Sounds like magic blower syndrome. The issue is most likely the clump of resistors in the HVAC box behind the evaporator.

DuncanF

Had a similar problem on my S4 earlier in the year. No fan or a/c unless I moved the slider to the defrost position. Very irritating considering how much effort I've put in to getting it all working.

Power goes through a different relay on defrost / demist so I wiggled the blower / ac relay and it sprang back to life. It's a normal 53B relay and I had a spare so I swapped it out and all good ever since.

Regards
Duncan