Another Climate Control Issue
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Joined: May 2010
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From: Mulvane Kansas
Another Climate Control Issue
I have a 1989 with the climate control. After as much troubleshooting as I can stand for one day, I will post to see if someone has had a similar experience. The problem is all I get is heat. The head control unit is in good shape, I cleaned all the contacts a couple of years ago, and all the lights and display function as they should. I have an extra programmer and did resolder the two big resistors, and tried the extra with no change. All vacuum controls from the programmer work as they should. I removed enough of the dash to gain access to the programmer motor and removed it to bench test. The motor will run in either direction with no issue and I left it in the middle of the travel when I re-installed in the car. At startup the motor returned the door to heat and it never moved again 
. What do I look at now?
. What do I look at now?
Le Mans Master
Joined: Jan 2006
Posts: 5,620
Likes: 206
From: Orlando FL
Did you check out the pot (rheostat) in the motor assembly to see if the resistance of the wiper is good in both directions.
Did you look at the gearing of the motor to see if all is in good shape. Teeth can break off or alignments may change if it's coming apart.
Have you had any of the gears out, the feedback pot requires alignment.
Did you look at the gearing of the motor to see if all is in good shape. Teeth can break off or alignments may change if it's coming apart.
Have you had any of the gears out, the feedback pot requires alignment.
Safety Car
Joined: Apr 2011
Posts: 3,660
Likes: 22
I have a 1989 with the climate control. After as much troubleshooting as I can stand for one day, I will post to see if someone has had a similar experience. The problem is all I get is heat. The head control unit is in good shape, I cleaned all the contacts a couple of years ago, and all the lights and display function as they should. I have an extra programmer and did resolder the two big resistors, and tried the extra with no change. All vacuum controls from the programmer work as they should. I removed enough of the dash to gain access to the programmer motor and removed it to bench test. The motor will run in either direction with no issue and I left it in the middle of the travel when I re-installed in the car. At startup the motor returned the door to heat and it never moved again . What do I look at now?
. What do I look at now?I guess the compressor is confirmed to be running?
The opt-68 elec a/c is 3 pieces that mean anything....programmer, control head, and BCM (blower module).
The control signal takes a loop path around the 3 items whenever a command is sent from the head. IF the command is sent from the control head...
Get your drawings out and find the correct wire at the control head plug and see if there is anything happening when you change commands, auto/econ/heat etc...
FSM should have the diagnostic for the elect a/c ...it does have onboard diagnostics. Its just a series of buttons to push and then watch the display for a code.
Control heads can be rebuilt for $150 thru Corvette America. Try taking the head apart and check the horizontal board for broken circuits at the plug. These things do wear out from vibration and eventually fail.
Thread Starter
Advanced
Joined: May 2010
Posts: 62
Likes: 0
From: Mulvane Kansas
Did you check out the pot (rheostat) in the motor assembly to see if the resistance of the wiper is good in both directions.
Did you look at the gearing of the motor to see if all is in good shape. Teeth can break off or alignments may change if it's coming apart.
Have you had any of the gears out, the feedback pot requires alignment.
Did you look at the gearing of the motor to see if all is in good shape. Teeth can break off or alignments may change if it's coming apart.
Have you had any of the gears out, the feedback pot requires alignment.
Are you refering to the bastard box over the gas pedal? Or the blend door servo located on the air box in the passenger floor/dash?
I guess the compressor is confirmed to be running?
The opt-68 elec a/c is 3 pieces that mean anything....programmer, control head, and BCM (blower module).
I guess the compressor is confirmed to be running?
The opt-68 elec a/c is 3 pieces that mean anything....programmer, control head, and BCM (blower module).
Thanks for your help, when I get some more time I will do some more research. These cars can test your patience at times.
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
The motor for the blend door is moved by the HVAC programmer above the gas pedal. It receives signals from the control head and applies DC voltages to the motor to make it move. The potentiometer attached to the blend door lever connects to the control head so it knows where the door is.
You can test the opening of the blend door by setting the temperature on the control head to the high and low limits (60 and 90 degrees). The gearing in the motor module is really high ratio, so it takes about 30 seconds or so to go from one end to the other.
I have a vague recollection that the control head calibrates the pot when you first turn on the ignition by running the blend door motor to the max heat and max cold positions. It does this so it knows where the limits are and then sets the door to the position commanded by the temperature set on the control head.
I have heard that the blend door motor module is also used on Cadillacs with electronic climate control, so that expands the potential sources if you need one. I'm sure the supply of new ones has run out after all these years, so you'll have to go used.
You can test the opening of the blend door by setting the temperature on the control head to the high and low limits (60 and 90 degrees). The gearing in the motor module is really high ratio, so it takes about 30 seconds or so to go from one end to the other.
I have a vague recollection that the control head calibrates the pot when you first turn on the ignition by running the blend door motor to the max heat and max cold positions. It does this so it knows where the limits are and then sets the door to the position commanded by the temperature set on the control head.
I have heard that the blend door motor module is also used on Cadillacs with electronic climate control, so that expands the potential sources if you need one. I'm sure the supply of new ones has run out after all these years, so you'll have to go used.
Drifting
Joined: Aug 2008
Posts: 1,921
Likes: 53
From: Philadelphia Pa
Just a thought....there's a sensor somewhere in the car that senses the temp and tells the system to supply heat/cold to get to the air temp to your desired temp. Check to make sure that sensor isn't "bad" and is calling for heat all the time.....
Le Mans Master
Joined: Dec 2000
Posts: 7,839
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From: San Diego, Ca
There's no gear on an '89. Motor is connected to the temp door lever with a plastic link. Those links do break so make sure it's in good shape and that it's not slipping when the door is pushed towards cold.
Motor should cycle between full hot and cold whenever the battery is disconnected or memory is removed from the System. That's how the Processor determines the position of the door. Yours only went half way, so assuming the plastic link is good, I'd suspect the Processor - Dash Controls for this Year. Cleaning the Contacts doesn't mean it's working right. For that, you'd have to know your way around the Board - I don't and I'm dangerous with a soldering iron anyway.
Inside and Outside Temp Thermistors have codes if they're not working (circuits open or grounded) which would be indicated by a flashing LED below the Outside Temp Readout. You could measure resistance of the Inside Temp Thermistor after it's sat overnight; and then again after it's sat in the sun. There should be a dramatic change (much less resistance when warm), and if so, rule out "garbage in/garbage out".
Motor should cycle between full hot and cold whenever the battery is disconnected or memory is removed from the System. That's how the Processor determines the position of the door. Yours only went half way, so assuming the plastic link is good, I'd suspect the Processor - Dash Controls for this Year. Cleaning the Contacts doesn't mean it's working right. For that, you'd have to know your way around the Board - I don't and I'm dangerous with a soldering iron anyway.
Inside and Outside Temp Thermistors have codes if they're not working (circuits open or grounded) which would be indicated by a flashing LED below the Outside Temp Readout. You could measure resistance of the Inside Temp Thermistor after it's sat overnight; and then again after it's sat in the sun. There should be a dramatic change (much less resistance when warm), and if so, rule out "garbage in/garbage out".
Le Mans Master
Joined: Jul 2007
Posts: 5,356
Likes: 2
From: No HOA, New Hampshire
Cruise-In X Veteran
St. Jude Donor '09
That sensor is right above the driver's head.
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Race Director
Joined: Apr 2002
Posts: 10,036
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From: Anaheim CA
You can put the C68 control head into diagnostic mode by pressing a magic combination of buttons which changed over the years and whether your car is a coupe or convertible. See this thread for more info:
http://forums.corvetteforum.com/c4-t...stic-mode.html
http://forums.corvetteforum.com/c4-t...stic-mode.html
Le Mans Master
Joined: Sep 2006
Posts: 6,050
Likes: 147
From: Phoenix AZ
2021 C4 of the Year - Modified Finalist
ok, the magic combination for 86-87 coupe is:
hold the rear defrost button and then press and release the manual up button.
change the item interrogated by pushing the warmer button.
hold the rear defrost button and then press and release the manual up button.
change the item interrogated by pushing the warmer button.
Last edited by coupeguy2001; Aug 11, 2012 at 01:34 AM.
Race Director
Joined: Apr 2002
Posts: 10,036
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From: Anaheim CA
