Dick K.

I have spent many hours diagnosing my problem and have developed a pretty good knowledge of what is happening...I just don't know the cause. Perhaps one of you will have some insight. If you like sleuthing out knotty problems, you'll love this one. Get a fresh cup of coffee, or whatever.

After the car has been sitting long enough for everything to be at ambient temperature (such as overnight), and when the 944 ignition is on (engine running or not), if the climate control temperature selector **** is full off (CCW), the heating solenoid valve clicks on and off, usually rapidly, sounding like a telegraph key. I know this to be a fact for I have removed the glove box and can feel the solenoid as it clicks. As the clicking occurs, the heater control valve on the engine side of the fire wall opens and closes (if the engine is running). What is happening is that the solenoid is getting current to turn on heat, turn off heat, etc...over and over in rapid-fire succession. The signal to energize the solenoid comes from, I assume, the climate control on the dash. This problem generally, but not always, diminishes as the car is driven for a half hour or more and everything comes to equilibrium, except it sometimes seems to be aggravated by hitting bumps, railroad crossings, etc. no matter how long I have been driving. Key term here is "sometimes." The problem does not occur if the temperature control is turned up so as to calling for heat- as in the cold driving season. I initially concluded that the cause was a faulty connection, maybe one with some oxidation that was making an intermittent connection, or a bad ground. I have removed and cleaned the connections on the temperature sensor under the dash, the connector for the solenoid, I have removed the climate control head and removed and cleaned the connectors of the back of it, I have even removed and cleaned fuse 29 that controls the climate control. I cannot find a separate ground for this system, though it may be there somewhere. My most recent attempt to fix this nagging problem was to remove the cover on the climate control head and reheat all the solder joints one at a time. I have found with other electronic devices that as they get old and develop intermittent problems that re-soldering the connections often solves the problem. None of these has fixed my problem. The cleaning of all the connectors seems to have reduced it, but not fixed it. I'm baffled.

Since the system otherwise works normally, I am prepared to put a toggle switch in a wire going to the heating solenoid valve, so I can just turn the system off in the warm season and turn it on in the cold system. I'd rather fix it the proper way, however. Any Ideas?

Jusii

Have you tried what happens if you run climate control unit disconnected? If still does it, problem isn't in the cc unit, if it doesn't problem could be in it.

And if you are at the solenoids, try hotwiring it, might be bad solenoid also.

And I have such a switch in my car by PO, it took me a year to figure out what that switch did.

Dick K.

I don't think removing the cc will tell me much because the the signal to energize the valve comes from the cc. Right?

Good idea to check the solenoid, though. Never occurred to me that it might be bad. I'll put a VOM across the connector to see if the current to the solenoid is steady. If so the solenoid is bad, if not the solenoid is OK. Thanks for the idea.

wesmc3

Did you ever sort this out? My car has no signal at the connector for the solenoids. I have tried three cc heads w/o any difference. All the other switches on the cc head work like they should.

Dick K.

I've never solved this problem. I've also substituted multiple CC heads (called Heater Control Switch). Different things happen at different times. Heat comes on when not called for- even with the A/C on in the middle of summer, fan levels 1 & 2 do not work sometimes- most of the time they do, the solenoids sometimes click repeadly like machine guns. I have checked every connection I can reach and all seem OK. I am convinced that there is a bad ground or connection somewhere in the system- but where? This car has always been in a fairly moist (humid) environment and I think there is just enough corrosion somewhere in some connector to cause a connection to be made or broken- right on the knife edge. Condition usually improves after driving awhile.

Any ideas or a solution sure would be appreciated

Dick K.

wesmc3

I don't have any wisdom. My solenoids will not click open to allow vacum to the heater valve. There is no 12v at the 4 pin connector that the two solenoids connect to. The car does seem to have a bad temp switch in the radiator. I am not hopeful that this is the problem since my other car opens the coolant valve even when the engine is cold.
If I get a chance to trace the wiring diagram tomorrow I will let you know where the wires go after the plug. It looks like they would go straight to the cc module or heater switch but since they dissapear into the bundle I can't say for sure yet.

Dick K.

Thanks for the offer. I'll look forward to learning what you find. I have made a discovery since my last post. Except for the fan motor operating all the functions on the CC switch- air recirc, defrost, A/C, even the lights stopped working. I removed the unit to find that the plug on the right side had worked loose (from vibration?), and thus power and signals were not reaching the unit. I cleaned all the contacts before reinserting and everything seemed to work correctly. I'm suspicious that since the plug could work loose that some of the connections (about 16 pins on each of two plugs) are spotty. I'm going to work on them and try to ensure a good contact.