LoFi

This is driving me mad, can someone please help . . .

The car has no air con and is a 1992 C4.

Here are the symptoms:

Some of the time all works fine, Air flows from all vents at the correct speed for the fan setting, the tempreture is even at all vents, the air can be directed at the windscreen, vent or footwells as you'd expect.

The remainder of the time, and this can happen mid journey, or from the start of a journey, the air from the centre and passenger vents goes very hot and blows hard. The drivers vent is normal. The power of the air from the centre and passenger vents cannot be controlled by the fan ****, it just keeps blasting. The air from the drivers vent is controlled by the fan ****. The only solution is to put the temp control on the blue dot. On most occassions moving off the blue dot returns the system to the furious rush of hot air from the centre and passenger vents. Sometimes however, it operates normally.

So far . . .
I have checked the servos, they all appear to operate correctly, although I haven't managed to catch them when the problems is occuring. The servos that direct the air work properly.

So what is happening . . .
My theory is that the servo for the passenger side sometimes gets stuck open but I cannot explain why the air flow is so great.

Any ideas most welcome . . . please.

Piers LoFi

dfinnegan

Sounds like the temp sensor on the back of the ECU is flaky

chewg

I noticed that the blower blows full blast when I accidentally disconnected my CCU (climate control unit) faceplate. Could it be that you have a bad connection in the CCU?

Good luck trouble shooting.

PorscheZen

i fixed flakiness in my hvac by replacing both the temp sensor and the resistor - that spring coil-y thing with two leads that inserts on the lower left side and in front of the temp sensor.

dfinnegan

Are you talking about items 10 and 12?

LoFi

I have no idea if the problem is fixed but folowing posts on here and some helpful PM advice from Adrian I gave a look at the rear blower this afternoon. The diagram posted by dfinnigan was very helpful, thanks.

Basically I confirmed that on blue dot the rear blower doesn't operate. Anywhere above that it blows slowly. Press defrost and the rear blower blows hard.

The outer sensor, marked 12, was very loose, and still is. The mounting (17) doesn't seem very good. It looks like it is supposed to insert and then twist to lock. Mine inserts and then twists but doesn't really latch and the lead it is attached to seems determined to unlatch the sensor. When I unplugged the sensor, even with the key out the rear blower starts.

The coily thing (10) (what does this do?) was hanging out of the pipe slightly. Not clipped in place. I pushed this back in and it seated correctly.

I then noticed that the rubber connector (6), from motor to pipe, was not seated properly. I also notoced that the pipe (5) at about 9 o'clock from the temp sensor was concertinaed and air was escaping between the pipe (5) and the rubber peice (6). The rubber peice (6) was also not properly seated under rear clip (9). I have put this right except the concertina in the pipe, which is too stiff the pull straight. I have blocked the air leak.

I will see if this make any difference, although it wouldn't logically explain the different speed of air from the fascia vents.

Thanks for the help so far

Piers

dfinnegan

Note that the resistor (#10) has been updated to part number 964 616 550 (02). If this is not what you have you should replace it. It's $20. Also, it should not be loose as it gets very hot and has been known to catch fire!

The temp sensor (#12) is seated into the pipe by twisting; as you've noted. Mine was similar to yours in that it would not seat properly. I discoverd that the cross shaped cut in the pipe had become deformed by a poor installation effort. The plastic between the cross cut outs was bent in toward the inside of the pipe and so they were not being correctly captured by the temp sensor clips.

I removed the pipe,force the bent bits of plastic outward a bit, reached inside with one hand and inserted the sensor with a twist whilst holding the bent bits of plastic into the correct position so that the clips could catch. Mine is now nice and snug in place.

You can then disconnect the wire when pulling the blower for working on the car rather than twisting and removing the whole sensor.

LoFi

I'll keep a close eye on the resistor, making sure it doesn't pop out. It seem pretty secure once back in. What does it actually do sat there in the air flow? I'll also check which part number I have.

Thanks

Piers