The Idaho Corvette Page

 Diagnostic Codes

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

 
 


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