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1990 - 1996 Corvette: HVAC Diagnostic Codes

On 1990 to 1996 Corvettes equipped with RPO C68 (electronic climate control), it is possible to read the HVAC system diagnostic codes from the climate control panel on the dashboard.

  1. To enter the diagnostic mode, press the fan up and down arrow buttons at the same time until -00 appears on the digital readout.

  2. One you have entered the diagnostic mode, you can scroll through the various parameters by using the up and down fan buttons.

  3. To view the value for a particular parameter, press the "AUTO" fan button.


Note:  If you see a "-" next to a parameter value (example: "-105"), you must add "100" to that value to obtain the correct value for that parameter. Therefore, the correct reading would be 205 for this example.

ParameterDescriptionValues
0 System Faults
(one of these will be set if your air conditioning controls have an LED flashing)
00=No Faults
01= Temp Door Motor Circuit Fault
02= Temp Door Motor Circuit Fault
03 = Ambient Sensor Open
04 = Ambient Sensor Short
05 = In-Vehicle Temp Sensor Open
06 = In-Vehicle Temp Sensor Short
07 = Solar Load Sensor Open
08 = Solar Load Sensor Short
09 = Low Freon Detected
10 = UART Failure
1 Temp Setting 60F to 90F
2 In-Car Temp Sensor 10 = HOT -130 = 230 = COLD
3 Outside Temp Sensor 10 = HOT -130 = 230 = COLD
4 Sun Load Sensor Max light Max Dark
L98 38 183
LT5 115 -110 = 210
5 Ignition System Voltage 0 = 9 Volts -155 = 255 = 16 V
6 Engine Speed (RPM divided by 25)  
7 Vehicle Speed  
9 A/C System Mode 00 = OFF
01 = Re-Circulation
02 = A/C
03 = Bi-Level
04 = Heater
06 = Defrost
07 = Vent
10 = Manual Re-Circulation
10 Blower PWM 0 = 0 Volts 128 = 14 Volts
11 Program Number 00 = COLD -155 = 255 = HOT
12 Mix Number -155 = 255 = COLD 00 = COLD
16 Coolant Temperature In degrees C  
17 Solar Correction 114 = Max light 128 = max dark
30 Stored Full Hot Value 0 to 50
31 Temp Door Travel Range 100 to 200
34 Temp Door Position Requested 00=Full HOT -153=253=Full COLD
35 Compressor On Time 0.1 second increments
36 Number Of Times Below Critical Time  
37 Software Version Number  
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Comments (1)
Comment by Nucman on Sat, Aug 2nd, 2014 at 9:26 AM
Thanks so much for sending me this, I am sure it will help. I reflushed the heater core and had very good flow, so I am sure its in the contols somewhere. I had to drive about 200 miles this week in 30 degree weather. I finally used duct tape to cover the vents near the windshield wipers and that kept the car a little warmer inside so I think it has something to do with the temp door. Unfortunely now I have another problem with my service engine light coming on and my code reader says it cannot get a connection. The car runs fine but when it gets to operating temprature and I stop at a light it starts idleing rough and the service engine light comes on, then it smooths out. The light is not on when i first start the car only after driving a while.....it just never ends !!!!!! But I do love my Vette. I will let you know how the heater thing goes.........THANKs Again !!
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