C68 Electronic HVAC Problem...
Thread Starter
Pro
Joined: May 2002
Posts: 518
Likes: 17
C68 Electronic HVAC Problem...
Hi all, I have a strange one here (on a 91 Z07 Coupe)...
Saturday the AC stopped blowing cold, and in fact the Heater was stuck on (even with the HVAC Controller set to "off").
I've done the following...
a) Check the HVAC Head for Codes ("00" = none).
b) Reset the HVAC Controller by removing battery for a couple of minutes (it went through it's 1.5 minute reset procedure and set no codes, but still was blowing hot etc).
c) Repeated "b".
d) Noted that the air is blowing out the correct Vents when selected, and that the Blower works correctly, and that the Compressor Clutch seems to be working.
Wierd huh?
Any ideas?
TIA, Doug
Saturday the AC stopped blowing cold, and in fact the Heater was stuck on (even with the HVAC Controller set to "off").
I've done the following...
a) Check the HVAC Head for Codes ("00" = none).
b) Reset the HVAC Controller by removing battery for a couple of minutes (it went through it's 1.5 minute reset procedure and set no codes, but still was blowing hot etc).
c) Repeated "b".
d) Noted that the air is blowing out the correct Vents when selected, and that the Blower works correctly, and that the Compressor Clutch seems to be working.
Wierd huh?
Any ideas?
TIA, Doug
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
There is a door in the evaporator housing that controls the flow of air through the evaporator and heater core. It is controlled by an electric motor on the heater plenum with it's linkage held together by a plastic connector. The connector may have broken or the motor may be shot, or rust and crud have accumulated around the lower pivot causing it to jam. To see if it's working, remove the blower module from the evaporator housing (left side facing forward) and then while someone operates the controls, see if the door moves between 60 and 90. If it's position doesn't change, try to move it with a screwdriver. Otherwise, remove the passenger's side hush panel to access the motor and it's linkage. Note, if you unplug the motor with the battery connected, that should set a code and the a/c won't operate until you disconnect the battery. Also, after it's unplugged or swapped out, there will be a no blower condition for a couple of minutes while the Programmer relearns the position of the door.
Thread Starter
Pro
Joined: May 2002
Posts: 518
Likes: 17
Thanks Gentlemen...
So, we're thinking either...
a) Mechanical problem with the Mix Door linkage, which would allow it not to work, though without setting a code?
b) The HVAC Controller has issues?
I'll check "a" tomorrow or Wednesday, and "b" if "a" fails...
Thanks...
Doug
So, we're thinking either...
a) Mechanical problem with the Mix Door linkage, which would allow it not to work, though without setting a code?
b) The HVAC Controller has issues?
I'll check "a" tomorrow or Wednesday, and "b" if "a" fails...
Thanks...
Doug
Le Mans Master
Joined: Jul 2001
Posts: 8,183
Likes: 3
From: Santa Maria, CA
Also note that the actuators/flaps/door system needs vacuum from the intake manifold to operate. Have a look at the line that comes from the back of the TPI manifold. Looks like this:
The tubing is brittle and breaks easily. Vac leaks out and the signal is not strong enough to move the mix door.
You might have loose solder joints on the circiut board of the controller. It is this unit:
Located in a black plastic box on the interior firewall by the steering column.
you can just resolder those points.
Let us know what you find. Goodluck.
The tubing is brittle and breaks easily. Vac leaks out and the signal is not strong enough to move the mix door.
You might have loose solder joints on the circiut board of the controller. It is this unit:
Located in a black plastic box on the interior firewall by the steering column.
you can just resolder those points.
Let us know what you find. Goodluck.
Thread Starter
Pro
Joined: May 2002
Posts: 518
Likes: 17
Wow, great help Gentlemen!
I haven't had the time yet, though I'm planning to pull the Blower Motor Sundaya sometime, and take a peak into the box.
The vaccuum is likely good as the various settings all seem to get the hot air out of the proper vents at the proper time etc...
One thing of note, was their used to be a pronounced rattle under the dash, and since the HVAC failure it's disappeared?
This might help point to the mechanical problem as well?
Again, many thanks to everyone for the great help!
Will advise soon...
Doug
I haven't had the time yet, though I'm planning to pull the Blower Motor Sundaya sometime, and take a peak into the box.
The vaccuum is likely good as the various settings all seem to get the hot air out of the proper vents at the proper time etc...
One thing of note, was their used to be a pronounced rattle under the dash, and since the HVAC failure it's disappeared?
This might help point to the mechanical problem as well?
Again, many thanks to everyone for the great help!
Will advise soon...
Doug
Thread Starter
Pro
Joined: May 2002
Posts: 518
Likes: 17
OK, what I'm assuming is the Temp Door moves ok...
When the engine is cold and off,with the ignition on, running the HVAC Temp up and down to max opens and closes the door.
What I find strange is that the HVAC Controller set no codes when the Blower was removed, and..., the Blower worked fine when it was reinstalled? I was under the impression that one needed to clear the codes before the Blower would operate etc?
Anyway, vaccuum appears to be fine as well, as the air flow appears at the proper vent at the proper time?
Maybe it's charge is gone, though it should throw a code for that as well shouldn't it?
Thanks again...
Doug
When the engine is cold and off,with the ignition on, running the HVAC Temp up and down to max opens and closes the door.
What I find strange is that the HVAC Controller set no codes when the Blower was removed, and..., the Blower worked fine when it was reinstalled? I was under the impression that one needed to clear the codes before the Blower would operate etc?
Anyway, vaccuum appears to be fine as well, as the air flow appears at the proper vent at the proper time?
Maybe it's charge is gone, though it should throw a code for that as well shouldn't it?
Thanks again...
Doug
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Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Is the compressor coming on? Low charge should kick out a code 9. If it isn't coming on and there's no code, the pressure switch is faulty, or the ECM isn't getting an "on" signal, or the a/c clutch relay is dead. If the compressor is coming on, feel the line, right before it enters the evaporator housing on the bottom, and the top line. Both should be cold, with maybe the top line a tad cooler than the bottom. If not, charge is too low. Otherwise, with the door working, something is blocking air flow across the evaporator. There is a foam filter on the inlet side and a leaking evaporator will destroy it, plugging it up. Check the compressor first.
Thread Starter
Pro
Joined: May 2002
Posts: 518
Likes: 17
Yes, the Compressor appears to come on as the rpm fluctuates momentarily etc...
Will check the AC Lines, and the HVAC Params as reported by the HVAC Controller...
...and the charge too...
Thanks again for your help!
I'll report back soon...
Doug
Will check the AC Lines, and the HVAC Params as reported by the HVAC Controller...
...and the charge too...
Thanks again for your help!
I'll report back soon...
Doug
Burning Brakes
Joined: Nov 2002
Posts: 807
Likes: 21
From: Los Altos CA
I had similar symptoms. It was the programmer. I replaced it with a used one. I have heard that some solder joints in the programmer causes the problem but I have not checked that out. FYI, the temperature door is not vacuum controlled, it is an electric servo. If you have a vacuum problem, you will get ok temperature control but it will come out of the wrong vents.
