A/C clutch diode location.
Thread Starter
Heel & Toe
Joined: May 2002
Posts: 21
Likes: 0
From: San Diego CA
A/C clutch diode location.
I have a 1990 C4 Corvette L98 with electronic climate control. With the ignition on, the control head works fine. After starting the engine, the control head flashes LEDs moving from one button to another and the buttons are inoperative (second set of control head and programmer reacts the same and no errors in the diagnostic display). I noted a clicking precedes the control head flashing LEDs. Since the compressor control shares electrical power circuits with electronic climate control (8A-67-0,1 in FSM), I suspect that there may be power spikes coming from the compressor clutch. I turned up the temperature to 85 degrees and then started the car. It ran for two minutes with the control head reacting normally before going wacky. I turned the temperature down to 65 degrees and started the car. It ran for about five seconds before the clutch kicked in and the control head went wacky. The FSM shows a A/C Compressor Clutch Diode to prevent voltage spikes which is taped inside the harness. I stripped the tape from the harness (picture included) at the A/C clutch connector but could not find any diode. Am I looking in the right place?
Safety Car
Joined: Aug 2009
Posts: 3,752
Likes: 276
From: Melbourne, Victoria, Australia
I have a 1990 C4 Corvette L98 with electronic climate control. With the ignition on, the control head works fine. After starting the engine, the control head flashes LEDs moving from one button to another and the buttons are inoperative (second set of control head and programmer reacts the same and no errors in the diagnostic display). I noted a clicking precedes the control head flashing LEDs. Since the compressor control shares electrical power circuits with electronic climate control (8A-67-0,1 in FSM), I suspect that there may be power spikes coming from the compressor clutch. I turned up the temperature to 85 degrees and then started the car. It ran for two minutes with the control head reacting normally before going wacky. I turned the temperature down to 65 degrees and started the car. It ran for about five seconds before the clutch kicked in and the control head went wacky. The FSM shows a A/C Compressor Clutch Diode to prevent voltage spikes which is taped inside the harness. I stripped the tape from the harness (picture included) at the A/C clutch connector but could not find any diode. Am I looking in the right place?
Just buy a diode and connect it across the a/c connector or wiring, the line or arrow goes toward the 12 volts check which one is 12v and which is ground.
See my crude diagram below
Ground to diode >| 12v supply to compressor to diode
Melting Slicks
Joined: Jan 2014
Posts: 2,478
Likes: 254
From: Downers Grove Illinois
The power spike occurs when the clutch shuts off and is reverse polarity of the power applied to the clutch while on.
Team Owner
Joined: Sep 2003
Posts: 25,397
Likes: 2,741
How far back have you stripped the harness?
I believe that on most 'denso compressor connector the diode is likely maybe 3 - 4 inches towards the body harness. It's not like the older R4 where it's right at the connector.
I believe that on most 'denso compressor connector the diode is likely maybe 3 - 4 inches towards the body harness. It's not like the older R4 where it's right at the connector.
Last edited by WVZR-1; Apr 28, 2017 at 09:03 AM.
Advanced
Joined: Dec 2016
Posts: 65
Likes: 3
I just checked mine, since I thought I had seen it. My 87 has a diode across the terminals of the wiring plug on the compressor. There is a rubber boot and if I slide it back the diode is going across in a U shape in with the wires clamped to the (spade terminals I think).
Thread Starter
Heel & Toe
Joined: May 2002
Posts: 21
Likes: 0
From: San Diego CA
I added a diode across the compressor connector and the control head still flashes LEDs moving from one button to another. My display of parameter values came back. Parameter 31: TEMPERATURE DOOR TRAVEL RANGE (FSM 1C1-5) appears to be going in and out of range. I have recoded values of 128, -101 (201), -102 (202), -197 (297) from the control head display. Per my understanding of FSM 1C1-5, the range should be 100 to 200. However, no fault codes (Parameter 00 is 00). Is my understanding of FSM 1C1-5 correct?
