dme

trust me. It is your ac/heater controller. I've been through this before. Irritating clicking and bad or no temperature control. I tore my system apart, replaced all temperature sensors and the solenoids. Nothing worked until I replaced the control unit. Good luck. I think George at 944 Ecology might work on them. You can usually find a replacement on ebay for $50 to $100.

Cyrus951

Is it like a crackling/scratching sound coming from around the DME?
I used to get that noise every night when coming back from a friends house late at night, with my lights on..
The problem disappeared a couple months ago

Robert D

dme, you're saying the clicking noise is coming from my controller which has all of the switches on it in the middle of the dash? Or, is it the cause of the actual clicking? The reason I say this is the clicking went away now that the heat is coming out, before when the AC worked is when I'd hear the clicking...

Bri Bro

I didn't see any relays in the heater controller (is is the unit in the middle of the dash) when I replaced mine. The unit does control several motors and valves that control the flow of air in the car and they can make a clicking noise.

If you can get you hands on a know good unit, it isn't hard to swap it out. The unit is held in place by a couple of screws and has two plugs on the back of it. Odds are it will fix your problem.

mrfixit951

The heater controller unit, based on input from the user and the three temperature sensors, controls the fan motor, several servos motors, and a couple solenoid controlled vacuum actuators. When something in the control unit goes wrong (which is what I am trying to figure out at a circuit level), one particular solenoid controlled vacuum actuator receives an intermitant control signal. The click you hear is the solenoid pulsing on and off.

After much work in this area I agree with dme, find another heater control unit (hopefully good).

Do any vendors offer a rebuilt unit??

I really need to fix/replace mine, but my car is down. I had the "dreaded" air oil seperator O-ring failure. while in there I found a little too much play in the turbo, and now am trying to decide on what to do. Basic rebuit turbo, K27/6, K27/8, Garret..... I know what I want, but I am at the stage where I have two kids in braces.....

When my cars runs I will be working on it again.

Ben

dme

Yes, Ben is right. The controller is sending the solenoid a continuous on/off signal which causes the clicking sound. The controller is the cause of the problem and the clicking solenoid by the glove compartment is the symptom. I never did this, but I bet you could observe this bad signal at the solenoid with multimeter. This seems to be a fairly common failure. I've seen this thread show up many times over the years. If someone (mrfixit) could figure out the failure then they could make a small fortune or at least earn our undying gratitude.

Robert D

I bet this is the problem. I've also had a strange case with this control unit where the 1-3 fan settings wouldn't work and #4 would. To get 1-3 to come on I can push the defrost in halfway repeatedly, tapping it. It eventually made the air blow. I'll have to see if I can swap it out with the control unit on the '86. Thanks for the help, I'll let you know what happens when I swap.

mrfixit951

Robert D
The blower switch sounds like a different problem. I have heard that the ballast resistors used to slow the fan sometimes fail. This collaborates with only speed 4 working, it is full speed and does not use ballast resistors. The ballast resistors are wired in series, so if you lose speeds 1-3 then probably the resistors for speed number 3 is open or intermitant. These resistors are located in the HVAC unit under the black plastic tray in the engine compartment. You should be able to measure the resistance of each resistors with an ohm meter. If you find one that measures open, you found your problem.

Ben

Ben

hosrom_951

I asked befor if the solonoid units control the vacuum operation on both heater valve and a/c lines coming in through the firewall..........

I am asking because my heater is not working, tested the heater valve and it is fine, even when switching between the two vacuum lines on the firewall, the heater valve is not functioning........

dme

if I remember right, one of the solenoids will control the vacuum to the heater valve. The other one probably (read, I'm guessing) controls the air mix or recirculation. I'd have to trace it back down again and my back doesn't feel like doing that now.

hosrom_951

I knew that they were responsible (at least one of them) for the vacuum to the heater.

Anyone knows where i can get them (besides dealer)

CHD

For anyone looking at this old thread, DME is right. Had the clicking and intermittent heat. Changed out the climate control unit with a $500 used one from Sons Porsche parts (Ebay) and problem solved. Fan blows stronger now too.

dme

Wow, that was 20 years ago!
Tom over on ******** has published a Climate Control Diagnostics procedure that may help find the actual problem in the controller.
Ooops, I can't say C_a_r_p_o_k_e_s