boca928

my 1985 928... at times I get in turn the a/c fan on and it works....5 minutes later its off... then an hour later its on....... is it a loose wire? something electronic overheating? The car is new to me, and I am not a mechanic but I would like to know what it can be... I will bring the car in to get looked at soon, and I have a large growing list for the mechanic to fix and hopefully upgrade this car to how it was in 1985... I feel if I own it... I should make it as it was when new or the best it can be..... I know I will be dumping $ in that I will never get out, but I don't plan on selling the car unless garage space becomes an issue.... Pete in smithtown long island will be getting the car soon to work his magic

FredR

Classic cause of your reported symptom is the relay in the HVAC control unit in the dash panel. Once the relay gets warm it is a crap shoot as to whether it works or not.

Jfrahm

Sounds like you are talking about the climate control blower (AC, heat and defrost) and not specifically the AC. Could be the switch in the climate control head or the blower motor is worn out and binding sometimes, or wiring in between. Maybe the resistor pack but I think that's usually an issue that affects the lower fan speeds or causes "Magic Blower Syndrome"

https://members.rennlist.com/pirtle/svc_blo.html

There is a connector near the MAF but under the cowl cover where you can check power to the blower, however I suggest testing this with a good-sized test lamp rather than a DMM as the DMM might show voltage with no load but the circuit might break down under load. The blower can pull something like 20 amps, more than 2 headlights. Or you could backprobe the connector to test the voltage with the blower still in-circuit.

-Joel.

Jfrahm

Fred are you talking about the relay that controls the AC compressor clutch? If his AC cooling is crapping out and blowing warm air that could be it. I install an aftermarket foglight-style relay near the jump post to take the current to keep this undersized relay from dying. The relay in the dash then only has to energize the foglight relay. Fused power from the jump post goes through the foglight relay to the AC compressor.
These relays have a handy mounting tab and you can get them with fused wiring for an easy mod. It might even save a dying relay in the HVAC head.

928NOOBIE

Freeze switch probe could need adjustment...

gbgastowers

Can you elaborate on this or post a link. My ac head unit relay is working so I think I want to do what you are saying. I bought a relay (pictured) but I also heard to use a 53 relay at the jump post ( with a diode added??? for something)

FredR

Joel,

I was reacting to the title of the thread but after seeing your post I note that in the body of the OP's original submission he appears to be saying the it is the blower that is switching on and off and if that is a correct interpretation then the problem is not going to be the relay or so I would think.

I the relay is the problem then as you say an alternate solution is to power the a/c clutch from a fused external relay powered from the hot post. Then the original relay is used to switch the external relay and the much lower current does not upset the compromised relay that bombs out when supplying the 3 amps or so needed to drive the solenoid. The trouble with this approach is the original relay may eventually crap out altogether .

vanster

I took out my head unit and sent it to Greg Brown. Sure enough the relay was out. He replaced it with a hearter relay and I put a fuse link at the freeze switch