This is my first post asking for advise on a heavy problem. I have a ’93, 6 speed, black coupe. My problem at present is with my a/c. When I first turn it on “AUTO” the display shows the temperature, but not the fan speed. I have to set the fan speed and the degrees manually. When I do this the system stays on with cold air coming out of the outlets as it’s supposed to do but does not cycle as per the manual. I was willing to let it work this way, as I understand that the parts are pretty expensive. Well, today the system decided to quit on me. The display indicated with blinking lights that there was a problem and the cold system shutdown. The compressor shut down. I know that if I disconnect the battery for a minute I can get the system back. But it won’t last. I disconnected the a/c fuses having to do with the a/c system, and it set the computer back but the warning lights over the mode switch blinked and shut the compressor down. I’ve checked the blower power module and it seems to be working. What I have to check is the heater and a/c programmer, which I’ll do tomorrow morning. Before the shut down all the modes worked manually. Two weeks ago I replaced the compressor, clutch and pulley because the compressor locked up. A system flush and recharge was also performed. Before this was done the system was doing the same as it is now. Has anyone had this problem? What did you find? I really need help. I’ve been reading the forum for the past 2 years, prior to purchasing this babe, and you guys are the greatest in getting these babes back to life. I haven’t had any problems prior to this one, outside of basic stuff you have covered in previous posts. Thanks.

 

I believe there is a listing in the tech tips that tells you how to pull the codes out of the A/C unit to diagnose the problem. I was having a problem with mine where my cooling fan wouldn't come on and the HVAC said it had low freon. I disconnected the battery for about a minute and now everything is working again.

 

I have a similar problem, auto mode would engage without my selection. Problem was that the temperature was fixed in the higher temperature.
I also removed the fuse from the AC and it can be disengaged. I do not understand why, but it works without the AC fuse.
I will check the Haynes and and will be in contact with you to share some probable solutions.
Curiously y have a 94 ZF6, that is almost the same or the same.

 

You do need to clear the memory once recharged and disonnecting and reconnecting the battery is the best way to do that.

System monitors the low and high pressure switches to determine whether or not the charge is too low or too high for safe operation. Check connections at both - particularly the low pressure switch. If it is momentarily losing its connection with enough frequency to cause it to cycle rapidly, the PCM will interpret this as a low charge and shut it down. I had this happen on my old S10 and another member had the same problem with his C4. The cure - for me at least - was a new low pressure switch. I think our fellow member had to replace the connector. The best way I know to troubleshoot it is to physically hold the connection on the switch and then see what happens - OR - wriggling it around should reveal if it's intermittent.

The high pressure switch/sensor is easier to troubleshoot with a scanner. It gets a 5 volt reference from the PCM and the resistance in the sensor decreases as the pressure goes up. For the PCM to ground the compressor relay, it needs to see about .8 volts to 4.0 volts on this sensor with each volt being about 100 psi. A scan will give you the volts and the pressure. Otherwise, I believe the return signal is a Black/Red Wire, ground is Black and the reference is some other color, but it doesn't matter - just put your DVM on each wire and see what the voltage is.

 

It could be that the controller itself is bad. You can also have some dirt or corrosion in the wire harness connection. It's common for the wiring harness contacts to have a film on them that prevents good electrical contact and that can be cleaned off with a simple pencil eraser.

These two links from the C4 Tech Tips may help:
https://www.corvetteforum.com/techti...D=92&TopicID=2
and: https://www.corvetteforum.com/techti...=118&TopicID=2

This tip show how to display the C68 trouble codes:
https://www.corvetteforum.com/techti...=193&TopicID=2