Originally Posted by JimPell
Thanks.I 'm going to have a hell of time,pretty big.
Does your 1987 C4 Vette have the C68 Digital display automatic climate control ?
Or do You have the standard manual twist controls for the HVAC functions & blower motor speeds ?
The C68 1986 to 1989 Corvettes had a underdash solenoid circuit board for all HVAC functions.
Electric over engine vacuum functional control.
If you have the C68 system, check for engine vacuum input source to this solenoid vacuum control circuit board.
An old vacuum gauge or Mighty Vac vacuum tester would be helpful making your own troubleshooting checks.
If the control head is dead, cleaning switch contacts & connector don't bring it back to life,
each year of early C4 C68 system control head has its own part # for service replacement.
& its different control heads from a Coupe & Convertible per model year.
To verify this fact, take a look at the driver's & passenger mirror on your 1987. Does it have the small glass etched symbol for heated mirrors?
My 1987 Vert does have the heated mirror symbols on each.
That is difference, extra NPN transistor or SCR - silicone controlled rectifier in C68 control head to turn on heated mirrors with HVAC front windshield defroster turned on for models with heated mirrors.
Heated mirrors only used on early C4's Verts with C68 HVAC option.