You can read the HVAC system diagnostic codes from your climate control unit if your 1990 to 1996 Vette is equiped with RPO C68. To enter diagnostic mode, push and hold the fan up arrow and down arrow at the same time until the LCD shows -00 You are now in diagnostic mode and may select any parameter using the up and down arrows. To see the value for that parameter, press the fan "auto" button.
Note: A minus sign on the display range means to add 100 to the value displayed. So, -155 actually is 255.
Parameter Number | Parameter Description | Valid Values |
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 [Notice the solar shield effect!] |
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 | .1 second increments |
36 | Number Of Times Below Critical Time | |
37 | Software Version Number |