It exceeded 60 degrees today here in Chicago - funny thing while driving my 928 today the heat didnt work. I moved the slide bar to cold then hot and no change. The unit does work as I was able to change the air from top to bottom, and fan speed.

The coolant level is fine. The hot water valve is about 2 years old - could it be this?

When I worked on my A/C Heater system 2 years ago, I replaced the A/C heater control, the hot water valve, replaced vacuum hoses and even replaced the interior and exterior temp sensors.

Could this be a fuse or relay?

Relay XVIII Cooling-Air Flap System?

Thanks in Advance!

 

Pretty unusual!! The normal 928 complaint is about not being able to get the heat off!

The water valve almost invariably fails ON, rather than OFF, since it is spring-loaded ON, and pulled OFF by vacuum. Possible that it is the problem, but not too likely. You can look at it pretty easily by pulling the air filter housing and looking down between the engine and the firewall. Have someone move the temp lever from full hot to full cool and see if the valve moves.

If the temp sensor string goes out, the temp lever normally will give you full heat on the right end or full cold on the left end, and nothing in between, so this doesn't sound too likely.

Two main possibilities that I see at the moment are:
Something is blocking the coolant flow to the heater.
The setting motor on the driver's side of the HVAC case isn't moving the temp control flaps. You can pull the left console side cover and see the setting motor - it's a black box about 4" by 6", mounted vertically. There is an arm sticking out of the top that moves a rod on the side of the case. With the engine running, move the temp lever to full hot, wait a minute or so, and move the temp lever to full cold while watching for the arm and rod to move. If the setting motor moves the temp flaps, the control system is probably OK.

Let us know what you find.

 

On my '89, I had no heat after replacing the Hot water valve. It would hold closed to allow the AC to go full blast, but would not open again. I traced it to be a bad solenoid(located behind the radio and AC controls). The new solenoid was about $35.
Pull the vaccum line from your Hot water valve to let it open. If you get heat, then you may have the same problem. To source it further, pull the strip from the center console with all the vaccum lines and solenoids attached(easy but somewhat tedious). Temporarily switch the vaccum to a different solenoid to see if you can get it to work. Remember to hook up the vaccum at the water valve again before doing this.

 

Just getting started on the heater problem.

Looked at the hot water valve. The actuator arm moves but only when you turn the entire Heater unit off or on. You know, the far left setting on the unit.

It does not move with the temp bar.

Does this sound right?

 

Jerry,

I just had this problem a few days ago. It turned out to be a loose connector on the setting motor. I re-seated it and checked the actuator movement in reponse to the temp setting on the control. There was little time delay in response to a change in setting but within a few seconds, the actuator should move.

BTW, mine is an '81... I'm not sure yours works the same way.

 

Thanks John, where is the setting motor?

 

Jerry,

sorry for the delay, I hadn't checked back in a while. The setting motor on mine is under the dash on the drivers side near where the console meets the dash. If your sitting in the drivers seat, it would be in the vacinity above and to the right of your right knee. Its a black box as Wally described in his post, with connectors on one edge and a lever between it and the main HVAC contol box. If that arm doesn't move in response to the tempurature selector, that would explain your lack of heat. Why it isn't moving might then be the real question... mine was just a loose connector. Good luck.

 

Thanks for the replies. I am going after it again tomorrow. Question, I want to remove the heater/ac control unit in the center.

I cant remember exactly how I popped off all the trim on the console area - I think I just gently pried it off. Anyone got he specifics of doing this?

Thanks in advance.

 

Yep - just gently pry the trim out using a small putty knife.

 

I finally got heat in my Shark. Believe it or not I still need it here in Chicago.

Thanks for the replies guys, it really helped. I also used the Porsche Manual on Heating/ A/C to understand the layout but you guys got me in the right direction.

I found that the adjusting rod to the mixing motor was gone. I finally found it under my mat and reinstalled it and I have heat. The motor happened to be in the cold position when the rod fell out so I was getting no heat. I guess the opposite could happen and you would only get heat - maybe some of the problems others are having.

I am posting a picture of the rod and motor. Also, a picture of the manual that helped. Thanks again - this board is amazing.

 

Jerry-

Be sure to make the adjustments per the SM's - or you may experience 'not as cold A/C' this summer.