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Help with AC and Cruise please


Well-known member
May 23, 2001
1985 Bright Red Rocket
Hello Ok when I bought this car I found a "electronic Relay" burnt out in the back storage comp. I have no Idea what it does...

but My AC does not work the Compressor is full ( I checked) but when I turn it on the pump doesnt even engage

Also with the cruise...ARG! I have NO idea whats wrong with it... is there a common problem for this I should know about?
Whoops that relay is about 2"x3" and about 3/4 thick its black and has one row of pins.. And I cant make out the model #'s
Hey BigRed

I'm not an authority on mechanical/electrical car anything. Hubby does most of the work on our 78, I watch, listen, learn and sometimes actually DO minor repairs. WITH instructions!
Our cruise control also doesn't work, but I've seen in the Vette catalogs that there is some kind of regulator (may be wrong term) that controls the cruise, and that may need replacing. I am not in a hurry to fix our cruise because I don't take long drives and I prefer to "drive" it myself.
I'd try to find out what the burnt relay controls before doing any fixes...that may simply cure your problems. Do you have a Chiltons, Haynes or Vette Assembly Manual?
AC is WAY beyond me...I took mine to a shop to upgrade to the new coolant. ($):(

First off I would buy a manual for the car. I went and bought three of them, Chiltons, Clymer and Haynes. Each has something better then the other, but the bottom line is, that there is not a better way to learn what your car is all about.With these three manuals I have been able to fix everything that was wrong with my 85 after 16 years of abuse and jackleg backyard mechanics. I am much happier now that everything works, I did it myself and I know what was done, where it was done, how it was done and that it was done right.
Cruise...the module that controls the cruise is in the front drivers side in front of the wheel under the headlight, lift the hood and you will find it on the wall near the ball shaped vacuum canister.
I would also check the fuses...now another thing I found was the vacuum lines. From the canister there is a vacuum line that goes to the cruise control and then tee's off to the TPI plenum on the passenger side rear just in front of the distributor.There you will find 2 vac supply ports, the front one goes to the egr control relay, the one in the rear goes to the cruise control and supplies the interior a/c and heating ducting. connected to the rear port is a cruise control check valve. The cruise control and interior vac line is connected to this check valve. If this valve is bad, your interior a/c and heat controls will not work, you will not be able to control the direction of air inside, air comes out of everything all at once, the cruise control will malfunction as well. Check all the vac lines for breakage especially where the connect. The air conditioning also has fuses and check the connector on the compressor. Plus there just so happenes to be an a/c power control relay. I have searched all three manuals and none show where it is supposed to be. Wish I could be of more help...take care and good luck...
AC cruise next

Does your 85 have manual AC ( not climate control)
How much charge do you have in the AC system static
60-80 psi?

I have never seen the cruise control stuff "under the headlight... the controller is part of the dash cluster that's where the colum switch/ speedo /brake switch / and servo connect to.

My cruise is still blinko! I have replaced ALL the vac lines (mine were rotted). The number 1 failure is the servo #2 is the colum switch I fear my problem is the cluster.

Give me more info... will be glad to help

Well my friend, 2 of the three manuals I have show the cruise control module on the wall next to the evaporative cannister and the vacuum cannister. My cruise control now works because I spent some time learning where all the components were and what they did. It is easy if you read and learn.
Now the trouble shooting chart for the cruise control goes like this...if it does not work at all...
1. blown fuse
2. short or open cruise circuit
3. faulty brake or clutch switch
4. leaking vacuum circuit
5. faulty cruise control switch
6. faulty stepper motor
7. faulty transducer
8. faulty speed sensor
9. faulty cruise control module
Cruise oopsie

I stand corrected, there is a module by the Evap can.....

my humble apologies

No apology necessary , my friend, but accepted never the less.
The beauty of sites like this is that we get to share, idea's, knowledge and friendship. And we get to learn, and it is free!
I cannot stand having to take anything to somebody's shop. I would just as soon do it myself and KNOW it was done right. So when I bought my vette , the first thing I did was buy every tech manual I could find and read each cover to cover, then went and covered the car from front bumper to the rear bumper till I knew where everything is and what it does. Then I set to fix all that was wrong. That is how I knew where the module for the cruise was and how to fix mine. Not to mention the A/C, blower motor and windshield washer motor. Just this evening I fixed the rear hatch solenoid, fixed the check engine light. Read the codes and fixed all the related problems...now no more light!
Now I recall you said your cruise did not work...need help?
Can't find the relay by the evap...


Ok I've seen the picture in the book.

I went to the wrecking yard and found the connector ( 5 pin black in line like 84 cooling fan relay).Left side fwd.

I've re read the GM shop manual... and there is no written mention of it in the schematic
(Supplemental electrical diag book 8A pages 33-35 )

Where is the damn thing located? my best guess is on the inside of the frame rail between the radiator and the frame... can you confirm this?

2nd is it a relay or other device?

My speed sensor works, Vac hoses are all new, column switch buzzes out, I though It was the vac soloniod.

Sorry for not getting back sooner....the control module is on the panel in front of the drivers side front tire next to the vac cannister, not to be confused with the evap cannister in front of it.
The module contains all the "electronics" necessary to make the cruise work. It takes the signals from the ECM, speed sensors, brake, and controls on the turn signal arm to control how the cruise works. Basically it tells the servo when to hold vac (maintain speed) and when to vent (release). On the back of the servo there is a connector, check it for corrosion and that it is making good connection. The control module also has a connector which should be checked. That was what was wrong with mine...some loose connectors and split vac hoses. Once I cleared all those out of the way it now works well.
Arrgh... still can't find the module

ok Ive found the vac canister/headlight control module/evap can/evap breather relay/ but no cruise relay ( controller )

Can you post a pix, or know a website that has em


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