Heater woes on 944

rambog · 02-18-2008, 06:22 AM

Last fall, I purchased an 83 Porsche 944 (non-turbo). I noticed that the defroster would never stop even if the blower switch was off. The force of the air was slightly above simple convection. Also, it would always be hot regardless of where the temperature slides were located. Needless to say, I would always drive with the windows open and sunroof removed to stay out of the sauna.

At that time, I thought I might have to pull apart the dash to get at some faulty damper. When I finally pulled the car out of the garage (after fixing the clutch hydraulics and replacing the distributor/spark plug wires, etc.), I let the engine run for about 10 minutes. I noticed that the engine was overheating and the radiator fan did not kick on.

My next step is to replace the thermostat. Is this a wise move? Do you think it will address all my heating issues or what else do I need to look into?

Razorback1980 · Razorback1980's Garage

No, the overheating motor will not fix your heater problems. That will be more related to the controls in the dash or the hot water valve at the back of the engine behind the intake manifold. Make sure your cables are moving the hot water valve at the engine as sometimes they come loose on the water valve and don't turn it off. If they are moving the valve, then you need to replace the hot water valve or readjust the cable. Basically that valve shuts the water going into the heater core off and if the heat isn't being shut off, then the valve isn't being shut off or is water is leaking past the valve. The cables could also be disconnected from the controls on the dash. If you notice that when you move the slide inside that the cable on the water valve isn't moving, then you need to look at the slides inside the car. The continual air flowing through the system is normal I think.

The part that stuck out in my mind about the overheating problem is that the fan wasn't kicking on. Wouldn't you want to fix that first before you change the thermostat? At least that would be my approach. Fix the fan and then if it still overheats, look at what else might be causing the overheating issue. To fix the fan, look at blown fuses in the auxiliary fuse panel or the fan grounding switch on the radiator.

hpservertech · 02-18-2008, 10:07 AM

Like Razorback said, fix the bigger problem first. It's one thing to have heat, but another to have an engine that overheats and eventually blows a headgasket.

Fix the fans not working & the engine overheat first, then worry about being too hot.

Possible causes: Temp switch on radiator, air in system (try to bleed it), fuses

Check out www.clarks-garage.com for methods of troubleshooting this they are well documented there.

rambog · 02-18-2008, 12:13 PM

Yes, I definitely want to address the major issue. I mistakenly assumed that that a bad thermostat would prevent the cooling fans from coming on. Obviously, I was wrong. From looking at the clarks-garage site, I will investigate the temperature switch and cooling fan relay. Since the fuses are the easiest, however, I will check this first. According to clarks-garage, it is fuse 3 and 5 on the auxillary fuse panel. Could anyone direct me as to the location of the auxilary fuse panel? From another document, it looks like these fuses should be 16 amps but I could not find the location. (I am not in front of the car but all I recall was one fuse panel visible from the drivers seat under the dash. I don't recall another fuse panel).

Thanks for the good instruction.

Razorback1980 · Razorback1980's Garage

I don't have an early model so I'm not certain, but I believe the one under the dash is the correct one. Fuse 3 should be 25amp and Fuse 5 is 16..if I remember correctly. Use your volt meter and check for power coming through on Fuse 3 as it runs the slow speed fan so start there. That should feed pin 30 of the relay so you can just check for power there instead of searching for the fuse panel. Fuse 5 feeds power to pin A on the relay so again, just check for power there. The next thing to do is to jump the wires on the temperature switch on the radiator. That completes the ground for the fan motors and makes them run. If you have power on pin 30 and the temp switch is grounded, then you need to look at the resistors but let's see what you have so far.

hpservertech · 02-18-2008, 01:08 PM

ooh I had forgotten about those damn resistors. That was the 1st of 2nd thing I had to fix on mine, only because the wires had gotten so corroded and I eneded up breaking one. For your sake let's hope it's not that. Easy to fix, but a pain in the but since you have to be laying on your back inside the passanger seat to get to them.

rambog · 02-18-2008, 04:59 PM

I found the auxiliary fuse panel and fuse 3 and 5 look good. I took the fuses out and started the car. I then took a voltmeter and jumpered both 3 and 5 and did not receive any reading!

I could not find the location of the fan relay. In the parts ordering section, it seems that it only is available on 1985 and later editions. Clarks-garage describes the part for my car but it does not give a location- any insight would be most helpful.

It looks like I will have to put the car back on its blocks to get at the thermofan switch. It looks like I can only reach it from the bottom of the car. I will then take a look at the fan motor as well to see if I get resistance when I connect the leads.

I am not sure the fan relay will cause both fans to not operate. According to clarks-garage, a bad relay shoud still allow the driver's side fan to run at slow speed. The lack of voltage at the fuse panel bothers me.

rambog · 02-18-2008, 04:59 PM

I found the auxiliary fuse panel and fuse 3 and 5 look good. I took the fuses out and started the car. I then took a voltmeter and jumpered both 3 and 5 and did not receive any reading!

I could not find the location of the fan relay. In the parts ordering section, it seems that it only is available on 1985 and later editions. Clarks-garage describes the part for my car but it does not give a location- any insight would be most helpful.

It looks like I will have to put the car back on its blocks to get at the thermofan switch. It looks like I can only reach it from the bottom of the car. I will then take a look at the fan motor as well to see if I get resistance when I connect the leads.

I am not sure the fan relay will cause both fans to not operate. According to clarks-garage, a bad relay shoud still allow the driver's side fan to run at slow speed. The lack of voltage at the fuse panel bothers me.

hpservertech · 02-18-2008, 05:14 PM

I would start cleaning grounds. It's usually the #1 cause of electrical problems on our cars, espcially the early ones.

Razorback1980 · Razorback1980's Garage

Are you saying you have no power on either fuse 3 or 5? If that is the case, then you need to look at the fuse panel. They often loose connectivity and you don't get power across the main power leads. All power for the fans come from that fuse panel so until you get power on fuse 3 or 5, the fans will not work on either low or high speeds. Here is the wiring diagram for your car, maybe that will help you trace down the problem, but it appears your fuse panel needs to have the power lead cleaned until you get power to the power side of the fuse panel.