1994 C4 Coupe AC Control Head Problem
Thread Starter
Heel & Toe
Joined: Dec 2009
Posts: 18
Likes: 0
1994 C4 Coupe AC Control Head Problem
I replaced my ICM last week and after I did, AC would not work. During start, AC displays "75" degrees for about 3 seconds and then shows 2 dash lines on display. None of the control buttons work. Looked in owners manual and it said to reset the system by pulling two cb's (Radio control and Courtesy Lights) and resetting them after 60 seconds. No change. Any ideas out there?
Melting Slicks
Joined: Aug 1999
Posts: 2,240
Likes: 42
From: Baltimore, MD USA
The two fuses to pull would be AC Clutch and AC Prog.
The AC Clutch fuse is hot when the ignition is On.
The AC Prog fuse is hot all the time.
Remove the fuses for a couple of seconds then plug them back in.
Turn the ignition On. The system will recalibrate the position of the air mix
door and after it's done (takes about 30 seconds) the blower
motor will turn on.
Or disconnect and reconnect the negative battery terminal.
You'll have to reset the radio stations.
The AC Clutch fuse is hot when the ignition is On.
The AC Prog fuse is hot all the time.
Remove the fuses for a couple of seconds then plug them back in.
Turn the ignition On. The system will recalibrate the position of the air mix
door and after it's done (takes about 30 seconds) the blower
motor will turn on.
Or disconnect and reconnect the negative battery terminal.
You'll have to reset the radio stations.
Thread Starter
Heel & Toe
Joined: Dec 2009
Posts: 18
Likes: 0
Gave it a try.....pulled AC Clutch (#18 on fuse panel/ 10amp fuse) and AC Programmer (#43 on fuse panel/5 amp fuse). AC control Head lit up, showing "75" degrees for about 4 seconds and cool air started coming out of vents right away. Around 30 seconds later, the LED below the "OFF" button illuminated for 1 second and the "75" showed on the main LED Display, then promptly went blank.Pulled negative battery cable and got same results.....Any more ideas?
Melting Slicks
Joined: Aug 1999
Posts: 2,240
Likes: 42
From: Baltimore, MD USA
The --- in the display indicates the control head has lost communication
with the HVAC programmer.
The Control Head and HVAC Programmer are powered by the AC Clutch fuse.
The HVAC Prog fuse provides 12 volts to a memory chip inside the
Programmer which prevents the loss of some stored parameters when the
ignition is off.
If the parameters are lost, when you turn the ignition On, the unit
performs a recalibration of the blend door. From what I've noticed
as soon as the ignition is turned on, the display shows the outside
temperature. As the calibration process continues, you hear the
blend door motor moving from one extreme to the other and then
the blend door is moved to a known position. The blower motor
then turns on.
Really no way to tell which unit is at fault.
The dealer would use a Tech 1 to simulate the Control Head. If the Tech 1
can communicate with the Programmer it would indicated the Control Head is
bad. If no comm. with the Programmer, the Programmer is bad.
About the only thing you can do is reseat the connector on the back of
the HVAC Programmer and reseat the connector at the Programmer. The HVAC
Programmer is located high on the firewall above the gas pedal/above
the transmission hump.
with the HVAC programmer.
The Control Head and HVAC Programmer are powered by the AC Clutch fuse.
The HVAC Prog fuse provides 12 volts to a memory chip inside the
Programmer which prevents the loss of some stored parameters when the
ignition is off.
If the parameters are lost, when you turn the ignition On, the unit
performs a recalibration of the blend door. From what I've noticed
as soon as the ignition is turned on, the display shows the outside
temperature. As the calibration process continues, you hear the
blend door motor moving from one extreme to the other and then
the blend door is moved to a known position. The blower motor
then turns on.
Really no way to tell which unit is at fault.
The dealer would use a Tech 1 to simulate the Control Head. If the Tech 1
can communicate with the Programmer it would indicated the Control Head is
bad. If no comm. with the Programmer, the Programmer is bad.
About the only thing you can do is reseat the connector on the back of
the HVAC Programmer and reseat the connector at the Programmer. The HVAC
Programmer is located high on the firewall above the gas pedal/above
the transmission hump.
