Mr. Emefef,

Since you wired up separate switches to control the different functions, would you be so kind as to document your setup and what you did and found out?

Your effort won't be wasted and it may very well help someone else fix a problem!

 

There are endless threads on forums across the interweb about our climate control units. CHECK YOUR CLIPS! comes up often, as does YOU NEED A HEATER CONTROL VALVE.
As in many cases - people reply with what they know best in a genuine effort to help.
So -

• after you've checked and the clips holding the linkage to the flaps is good (mine were new, had an invoice from PO);
• you've checked the heater control valve (HCV);
• you've checked the vacuum lines to the solenoids, the HCV, and the reservoir canister;
• you've applied voltage to the flap motors and solenoids to see if they work; and
• you've gone even deeper, in accordance with the shop manual and checked the resistance across the three temperature sensors (by removing the CCU from the dash and testing across the appropriate wires in the harness,

you have to be wondering, why is this only blowing hot?
You've covered all the basic steps. Check to see if the CCU itself is getting voltage. There are two plugs, A and B. The wiring diagram will confirm this, but I believe at B2 you should have supply voltage. If you don't, the problem is between there and the battery (fuse).
If you do, it's likely the problem is internal. This is what I came up with, for two reasons. 1) I didn't want to spend money on a new unit and be wrong, and 2) I kept second-guessing my testing so I was really concerned there might be something else.

I made a Bond-esque panel with rocker switches to control everything I believed should work.
I cut a panel of aluminum that would fit in the opening below the radio, wrapped in black vinyl, and installed switches.
Two simple on/off rockers for:
1) open/close recirculation flap
2) open/close heater control valve.
The temperature is controlled by a mixing flap, and the floor and upper vents by flaps. These are three motors that have to operate in forward/reverse. I did that with momentary switches go forward/reverse. Simple example is power window switches, which is what I bought from the local electronics store. Altogether I spent less than $30 (CDN) on wire, connectors and switches.
To keep the blower fan switch, you need to leave the CCU in place. The fan switch has its own plug. I disconnected the other two plugs from the back, pulled my wires up from my switch panel (around the back and over the radio), and then pushed the ends of the wires into the appropriate female parts of the harness, and wrapped with tape (remember, wasn't supposed to be permanent. To determine the right connections, you just need look at the diagram - one side of each motor will go to a ground, the other to one of the other terminals. You can make all the grounds common (which i did on my switch plate) and have fewer wires to pull through.
Essentially, what I did was connect switches to all of the wires I had used to test each flap motor and solenoid, so I could try the hole system.
I didn't do anything with air conditioning, so I didn't expect it to work, BUT
EVERYTHING else worked.
Flip the rocker to turn on the HCV and I had heat - no magic there, but turn it off and voila! no more heat!
The temp control would have moved the mixing flap back and forth, which I did with a widow switch, moving it one way or the other.
The footwell and defrost sliders were also replaced by a window switch, dabbing at it to move flaps one way or the other.

Once I knew everything worked, I looked for a new one - and I had something that would work in the interim.

 

Nice! For a long time I've wanted to build a manual control panel for the HVAC system. Controlling the vacuum solenoids is simple enough, as are the fan, AC compressor, etc. I don't know how to control the mix flap or the top and bottom vents. Are they stepper motors? Did you just give them voltage to get them to move a bit?

I had a problem with my car, constant clicking noise, and unpredictable heat/no-heat. Replaced the CCU and the problem went away. The clicking was coming from the solenoid which controls vacuum to the HCV. So if you want to keep your CCU, you could hack the signal to that solenoid and leave your own override switch on it.

 

I opened my ccu and cleaned the boards and contacts..,ultimately i determined that there was no voltage at any of the outputs, so there must have been a problem with one of the components. I'm not that knowledgeable to have started testing each one.
As for the flap motors, I'm not sure what they are. I made the assumption that they ran in forward and reverse and wired them that way with momentary switches. I wouldn't leave it that way permanently because a) you don't know what position they're in other than by memory or feeling the air, and b) i dont know if there's a limit switch to stop sending voltage to the motor when the flap is fully opened or closed.

 

i remember reading a thread where the symptoms were closer to my car. every things works, it just does it when it feels like it. the poster bought a new pot resistor and soldered it in replacing the temp selector. problem of random heat and random temp selection gone. I bought the resistors but haven't soldered them in yet.

where did you get your new ccu?

*edit* here is the thread https://rennlist.com/forums/944-turb...diy-xpost.html