C68 hvac is stuck on the hot setting
03-09-2018, 05:16 PM
#1
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C68 hvac is stuck on the hot setting
My C68 hvac is stuck on the hot setting om my 1990 there are no codes no flashing lights both the head unit. And the programmer were sent to bate.com for repair because of fault code had them refitted two months ago worked ok Yesterday could not turn the heating down all the other functions work ie the blower speed,heated rear window the only other thing i noticed was when i hold in the two fan speed buttons for five seconds to enter diagnostic mode to two zeros only show once i release the buttons were as before they came on when the buttons were held down could the problem be a cracked gear wheel in the actuator ? 
Last edited by Gary Bagley; 03-10-2018 at 03:31 PM.
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Gary Bagley (03-10-2018)
03-09-2018, 07:44 PM
#3
Le Mans Master
My C68 hvac is stuck on the hot setting there are no codes no flashing lights both the head unit and the programmer were sent to bate.com for repair because of fault code had them refitted two months ago worked ok yesterday could not turn the heating down all the other functions work ie the blower speed heated rear window the only other thing i noticed was when i hold in the two fan speed buttons for five seconds to enter diagnostic mode to two zeros only how once i release the buttons were as before they came on when the buttons were held down could the problem be a cracked gear wheel in the actuator ?
OR
Can you control the display but heat is always coming out of the vents?
03-09-2018, 08:57 PM
#4
Race Director
Every so often my car does this. It will be stuck on 90 and won't go back down, or stuck on 60 and won't go back up. The control head contacts need to be cleaned in mine. Since I'm too lazy to do it, I just push on the trim piece directly adjacent whichever button isn't working and then press the button with my other hand. So far that has been working, at least for now.
03-10-2018, 02:13 AM
#5
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C68 HVAC system – Mix door problem - 94
Are you saying you can't control the digital display where when you adjust the temperature rocker switch and it will My C68 hvac is stuck on the hot setting there are no codes no flashing lights both the head unit and the programmer were sent to bate.com for repair because of fault code had them refitted two months ago worked ok yesterday could not turn the heating down all the other functions work ie the blower speed heated rear window the only other thing i noticed was when i hold in the two fan speed buttons for five seconds to enter diagnostic mode to two zeros only how once i release the buttons were as before they came on when the buttons were held down could the problem be a cracked gear wheel in the actuator ? , is it stuck at 90?
OR
Can you control the display but heat is always coming out of the vents?
OR
Can you control the display but heat is always coming out of the vents?
03-10-2018, 02:14 AM
#6
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C68 HVAC system – Mix door problem - 94
Sorry i did not make myself clear the display changes from 60 to 90 but the blend door will not move from the full hot Position
03-10-2018, 02:15 AM
#7
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C68 HVAC system – Mix door problem - 94
Every so often my car does this. It will be stuck on 90 and won't go back down, or stuck on 60 and won't go back up. The control head contacts need to be cleaned in mine. Since I'm too lazy to do it, I just push on the trim piece directly adjacent whichever button isn't working and then press the button with my other hand. So far that has been working, at least for now.
03-10-2018, 02:16 AM
#8
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C68 HVAC system – Mix door problem - 94
03-10-2018, 03:19 AM
#9
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C68 HVAC system – Mix door problem - 94
Sorry i did not make myself clear the display changes from 60 to 90 but the blend door will not move from the full hot Position
03-10-2018, 04:44 AM
#10
Race Director
On my 95 I can remove the blower motor resistor/transistor assembly (blower speed module) and look in the heater case with a flashlight. I can see the temp door move. Once a piece of the foam seal around the evap core came loose, and was caught inbetween the hvac case and the temp door. So it wouldn't move to full cold. All I had to do was reach in and take it out.
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Gary Bagley (03-10-2018)
03-10-2018, 05:56 AM
#11
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C68 HVAC system – Mix door problem - 94
On my 95 I can remove the blower motor resistor/transistor assembly (blower speed module) and look in the heater case with a flashlight. I can see the temp door move. Once a piece of the foam seal around the evap core came loose, and was caught inbetween the hvac case and the temp door. So it wouldn't move to full cold. All I had to do was reach in and take it out.
03-10-2018, 10:18 AM
#12
Le Mans Master
The programmer drives the blend door motor. I have repaired several programmers for bad capacitors which caused bad display information and no control on the control head, however never fixed one for this symptom but I guess it is possible.
The blend door motor should probably be looked at first. If the drain for the evaporator plugs up, the water will back up into the evaporator case and run into the motor. Over time it will rust and possible get jammed up. It's all plastic except for the motor which is the source of rust and debris.
Only two screws hold the motor on but you can't see it until you drop the plastic knee shield out of the way (that’s the big effort). It's keyed, only goes on one way and has a connector. You can then move the blend door with your fingers. It comes apart easy but don’t get the gears messed up as the feedback potentiometer is calibrated and if you get it misaligned it will never work correctly.
The blend door motor should probably be looked at first. If the drain for the evaporator plugs up, the water will back up into the evaporator case and run into the motor. Over time it will rust and possible get jammed up. It's all plastic except for the motor which is the source of rust and debris.
Only two screws hold the motor on but you can't see it until you drop the plastic knee shield out of the way (that’s the big effort). It's keyed, only goes on one way and has a connector. You can then move the blend door with your fingers. It comes apart easy but don’t get the gears messed up as the feedback potentiometer is calibrated and if you get it misaligned it will never work correctly.
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Gary Bagley (03-10-2018)
03-10-2018, 10:27 AM
#13
OP - punctuation might help!
What year?
Year matters when discussing the actuator operation. Your thoughts in your original post seem likely! Actuator location changes dependent upon year.
What year?
Year matters when discussing the actuator operation. Your thoughts in your original post seem likely! Actuator location changes dependent upon year.
03-10-2018, 02:56 PM
#14
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Heater/AC Problem (blend door
03-10-2018, 03:28 PM
#15
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C68 HVAC system – Mix door problem - 94
The programmer drives the blend door motor. I have repaired several programmers for bad capacitors which caused bad display information and no control on the control head, however never fixed one for this symptom but I guess it is possible.
The blend door motor should probably be looked at first. If the drain for the evaporator plugs up, the water will back up into the evaporator case and run into the motor. Over time it will rust and possible get jammed up. It's all plastic except for the motor which is the source of rust and debris.
Only two screws hold the motor on but you can't see it until you drop the plastic knee shield out of the way (that’s the big effort). It's keyed, only goes on one way and has a connector. You can then move the blend door with your fingers. It comes apart easy but don’t get the gears messed up as the feedback potentiometer is calibrated and if you get it misaligned it will never work correctly.
The blend door motor should probably be looked at first. If the drain for the evaporator plugs up, the water will back up into the evaporator case and run into the motor. Over time it will rust and possible get jammed up. It's all plastic except for the motor which is the source of rust and debris.
Only two screws hold the motor on but you can't see it until you drop the plastic knee shield out of the way (that’s the big effort). It's keyed, only goes on one way and has a connector. You can then move the blend door with your fingers. It comes apart easy but don’t get the gears messed up as the feedback potentiometer is calibrated and if you get it misaligned it will never work correctly.
03-10-2018, 03:34 PM
#16
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C68 HVAC system – Mix door problem - 94
But heat always comes out of vent blower speed works and vent controls
03-10-2018, 04:37 PM
#17
Le Mans Master
I also remember in the early programmers 2 resistors go bad and cause problems. Can't remember what, see what I can find.
Possibly some others more familiar with the early C4s will fill in the "gaps" in my advice and give some additional information.
Last edited by pcolt94; 03-11-2018 at 08:58 AM.
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Gary Bagley (03-11-2018)
03-11-2018, 03:27 AM
#18
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Well that does change my advice. From what I remember and reading the Forum, some of the earlier C4s used rods to connect the motor to the blend door. Don't know if the rods disconnect, something binds or if the motor just does not drive.
I also remember in the early programmers 2 resistors go bad and cause problems. Can't remember what, see what I can fine.
Possibly some others more familiar with the early C4s will fill in the "gaps" in my advice and give some additional information.
I also remember in the early programmers 2 resistors go bad and cause problems. Can't remember what, see what I can fine.
Possibly some others more familiar with the early C4s will fill in the "gaps" in my advice and give some additional information.
the 1990 has the blend door motor mounted on top of the heater box
03-11-2018, 03:34 AM
#19
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is it possible to access the lead for the blend door motor by removing the r/h carpeted panel.
to get to the lead like the one in the photo ?
Last edited by Gary Bagley; 03-11-2018 at 03:34 AM.
03-11-2018, 09:33 AM
#20
Melting Slicks
Member Since: Sep 2008
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Have a 90 when there are C68 head issues disconnecting the battery for a few seconds will reset it = normal operation.
Insure there is good vacuum the hose connection / connector @ the rear of the intake is prone to fail.
Good luck.
Insure there is good vacuum the hose connection / connector @ the rear of the intake is prone to fail.
Good luck.
