Published July 18, 2019 · Updated September 24, 2019
1990 to 1996 Corvette models that are equipped with the C68 option code (Automatic, Electronic Air Condition) allow HVAC diagnostic codes to be read from the digital screen on the climate control panel. This feature is useful when attempting to diagnose issues with the A/C system. To learn more about entering the diagnostic mode and diagnostic code descriptions, read below.
C4 A/C Climate Control Panel Rebuilding Service 1990-1996
DIAGNOSTIC MODE: ENTERED & EXPLAINED
To access the diagnostic mode, press and hold the climate control’s fan up and down arrow buttons at the same time until “-00” appears on the digital screen. Once the diagnostic mode is activated, the fan up and down buttons can be used to scroll through the various options. To view the value for a particular option, press the “AUTO” fan button.
NOTE: If you see a “-” next to a value, for example “-105”, the neagtive sign must be removed and a value of 100 must be added to the orginal value to obtain the correct value for that option. Therefore, the correct reading for the example above would be 105+100 = 205.
HVAC DIAGNOSTIC CODES & DESCRIPTIONS
The crew at Corvette Salvage has compiled a list of the option values, option descriptions and code values/descriptions. You can view this list below. If you need further assistance, you can open a support ticket at anytime by clicking here.
| Option Value | Option Description | HVAC Code / Code Description |
| 0 | System Faults (One of the following codes will be activated if the climate control has a flashing LED light.) |
01 / Temperature Door Motor Circuit Fault
02 / Temperature Door Motor Circuit Fault 03 / Ambient Sensor Open 04 / Ambient Sensor Short 05 / In-Vehicle Temperature Sensor Open 06 / In-Vehicle Temperature Sensor Short 07 / Solar Load Sensor Open 08 / Solar Load Sensor Short 09 / Low Freon Detected 10 / UART Failure |
| 1 | Temperature Setting | 60°F to 90°F |
| 3 | In-Vehicle Temperature Sensor |
10 / Hot
-130=230 / Cold |
| 4 | Sun Load Sensor |
L98/LT4 Engine
38 / Maximum Light
183 / Maximum Darkness
LT5 Engine 115 / Maximum Light -110 = 210 / Maximum Darkness |
| 5 | Ignition System Voltage |
0 / 9 Volts
-155 = 255 / 16 Volts |
| 6 | Engine Speed | RPM divided by 25 |
| 7 | Vehicle Speed |
|
| 9 | A/C System Mode |
00 / Off
01 / Recirculation 02 / A/C 03 / Bi-Level 04 / Heater 06 / Defrost 07 / Vent 10 / Manual Recirculation |
| 10 | Blower PWM |
0 / 0 Volts
128 / 14 Volts |
| 11 | Program Number |
00 / Cold
-155 = 255 / Hot |
| 12 | Mix Number |
00 / Cold
-155 = 255 / Cold |
| 16 | Coolant Temperature (°C) | Coolant Temperature in degrees Celsius (°C) |
| 17 | Solar Correction |
114 / Maximum Light
128 / Maximum Darkness |
| 30 | Stored Full Hot Value | 0 to 50 |
| 31 | Temperature Door Travel Range | 100 to 200 |
| 34 | Temperature 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 | Number of Times Below Critical Time |
| 37 | Software Version | Software Version |