Derek H

I think I have diagnosed the climate control system "brain" to be the source of my "no heat" problem. Using the troubleshooting procedure in the factory manuals, I discovered it takes ages for the brain to switch power to the heater/bypass flap control motor after selecting full heat. I believe that the full heat position (red dot on ****) should immediately activate the heater flap. After it has eventually "woken up" during a journey (can take anthing from a couple of minutes to 20-30 minutes or so), it seems to work ok until the next journey.

So, is there a fix for this problem, other than a new brain?

thanks

Derek H
'92 968 black/black
Linköping, Sweden

Operator

wow, ive never heard of someone having a "no heat" problem.. i thought everyone only had the "too much heat" problems

you are a blessed and lucky man! so your 968 only blows cold air?.. can we do experiments on his car so we can figure out how and why this is happening and how we can all have it happen to us?!

oh yea.. try cleaning the contacts on the back of your climate control brain (behind the 2 sliders and 2 *****) .. i think.. could help..

also maybe check the heater control valve (wherever it is on the 968) maybe its stuck open and just taking a long time to close.. lube it? jim will chime in.. im sure.. and he knows much more than me. still i want to know how i can have this problem

jim968

DeRek, if you haven't tried any repairs yet, pull the brain unit out of the dash & just try unplugging & replugging the connectors on the back of it. Sometimes these pins & sockets develop a little corrosion, and that interferes with the signals to & from the inputs (sensors) & outputs (motors & solenoid vacuum valves). AFAIK, this is mostly 5VDC circuitry, so it doesn't take much corrosion to cause problems.

Beyond that, you _might_ be able to get enough access to try resoldering some of the connections internally, if you pry the black plastic back cover off of the brain. But I know of no test procedure or equipment for the unit; AFAIK, all the testing that you could do would be limited to whatever basic electronic component testing you're capable of. I'd also consider that the motor & flap mechanism _might_ be the source of the sluggish operation.

The only other thing I can suggest is to check the heater valve operation, which you've probably done. It should be closed when vacuum is applied, and the engine off or vacuum failure position is open.

Let us know what you find out.

Jim... Lunch!!! <img src="graemlins/drink.gif" border="0" alt="[cherrsagai]" />

Derek H

Thanks for the inputs guys. However, regarding the heater valve, I have confirmed that the problem is in the control circuitry rather than the heater valve. The troubleshooting info in the manual says that I should get +10v at pin 5 on the connector to the heater/baffle flap motor when I select full heat on the controller. When do this, it takes a long time before the voltage changes from the 0.15 volts that is specified at pin 5 with the controller set to full cold. Even when I eventually get voltage, it seems to be only about 4 volts or so, but it is enough to move the motor to the full hot position. As I said before, after it "wakes up", it then responds quickly to changes in the temperature setting, until the car has been shut down for a while, and then it takes ages to "wake up" again. I have checked out the 3 temperature sensors and I am getting the correct resistances according to the data in the manual. Therefore, I am thinking that there is an electronic problem in the controller itself. I have pulled the connectors on the back of the controller and refitted them several times, although there is no sign of corrosion on the pins/sockets. I have removed the black cover that protects the circuitry on the controller and looked for dry solder joints or other signs.

I guess a new or good used control unit is probably my only option.

cheers

Derek