At 06:19 PM 12/15/00, Andrew B wrote:
>My heater stopped working. It still blows, but only blows cold air.
>
>I'm really hoping that I just blew a fuse or something, but does anyone have any suggestions on what I should look at?

Possibilities:
- No hot coolant because radiator is empty (as suggested by Jay K.).

- No hot coolant because the thermostat is stuck wide open. Does the radiator get warm? Is the upper radiator hose hot?

- Hot coolant is not getting to the heater because the heater valve is stuck shut (again, as suggest by Jay) or is commanded shut. Remove the plastic shield under the hood at the base of the windshield. Find the heater valve in the center. Crank the car, put the heater on full hot, and pull the vacuum line off of the valve connection while watching the valve arm. If the valve arm moves, and there is vacuum on the line, you have a HVAC control problem, possibly in the setting motor. If the valve arm doesn't move, reach down and wriggle it a bit to see if it is stuck. The valve should be open, allowing coolant flow, with no vacuum applied.

- Hot coolant is getting to the HVAC, but the system is stuck on full cold.
Check fuse #9, substituting a known good fuse. If the fuse is good, there may be a problem in the control system. Pull the left console carpet cover, and find the setting motor, which is a black box on the side of the HVAC system with an arm sticking out. With the engine running, and the HVAC on, move the temp control lever to full cold while watching the arm on the setting motor. Wait a moment, then move the temp lever to full hot. The arm should move. If the arm goes from full hot to full cold, and won't stop in the middle, the sensor string (outside air temp, inside air temp, temp lever) has a problem.

>I think that the water is too saturated with coolant. Could that be the problem? or does that just sound stupid?


No, it probably isn't the problem, and No, it doesn't sound stupid. In fact, too much anti-freeze/coolant in the coolant mix can cause serious
problems. Pure anti-freeze does not have the specific heat capacity to cool the engine in hot weather, and will freeze quicker than the proper 50/50 (or 60/40) mix in cold weather.

Wally Plumley
928 Specialists

Here's another very good info from Wally: WallyHVAC.pdf

There is a servomotor that controls your heat, located above the driver's right knee. You must remove the parcel shelf to get at it. It has a little arm which controls the temperature mixer flap. If the arm is all the way up, you get max heat; all the way down, no heat. Normal position with the inside temperature stable is roughly
horizontal. So the first step is to find out what that little arm is doing. With the parcel shelf out, you can feel its position while sitting in the driver's seat. If it never stops anywhere but all the way up or all the way down, you have isolated the problem somewhat.

The key input to the servomotor is pin 4 of the upper plug (there are two). It connects to the outside temp sensor (in the air duct to the alternator), which connects to the inside temp sensor (behind the slotted fitting in the dash next to the glove box), which connects to a rheostat on the temperature control slider. According to the manual, the resistance between pins 4 and 12 should be about 3.7Kohms with the slider at 18, and about 4.7 Kohms with the slider at 30. I think that assumes approximately room temperature for the sensors.

Now, if there is any break in the chain from outside temp sensor to inside temp sensor to temperature control slider, you will get the binary temperature problem.
So check that reading, if you're electrically inclined. If it's wildly different, you've found the problem. If not, maybe you'll be lucky and the connector just needed reseating.

 

Interior temp sensor blower.