88 Silverado K1500 HVAC issue

[rm31859]

Hello all, I have an 88 Silverado K1500 that I am having a problem with and I hope someone can help. This truck has the electronic climate control with the LCD display. It quit working several days ago and now I have no HVAC. I have checked every fuse and circuit breaker, I have replaced the control panel itself with a good used one, I have checked the connections on the blower and nothing has helped. Any guidance would be appreciated. Thanks

[Palf70Step]

Your LCD area is part of the circuitry for the AC. They are probably not cheap new, so I'd see if I can find a used one in a parts yard to get the AC going again.

[ChevyTech]

Does the panel light up?

Is it the fan that does not work? Maybe a bad fan motor, fan resistors, or fan relay?

Welcome to the board!

[rm31859]

I replaced the fan motor about 3 months ago and everything was working fine until about a week ago. The LCD panel does not light up and the fan does not work. I tried replacing the LCD control panel with a known good used one and still nothing works.

[ChevyTech]

It is time to start testing the wires to the control head.

On one end of the connector for the control head the should be a red wire in terminal position #12, and a brown wire across from it.
The red wire should have power all the time and the brown wire should have power when the key is on.

The ground is a black wire in terminal #8

Test them.


You may find the schematic in this thread:
http://67-72chevytrucks.com/vboard/s...d.php?t=465744

[rm31859]

Hi all, I checked the voltages on the Red and Brown wires. The brown was reading 13.8 when the ignition switch was on but the Red was reading only 8.5. I don't know if a voltage reduction of around 5 would cause the control head not to work or not. The switch backlighting works when I turn the headlights on but the LCD screen will still not work. Thanks

[ChevyTech]

The red wire should read full battery voltage.

The first thing I would do is check and see if there are any loose nuts at the battery junction block under the hood on the passenger side of the fire wall. That is where the red wire gets its power from. The red wire should connect to the end terminal on the left end and is the same spot the wire to the battery connects. I would test the voltage on all wires connected to the junction block. They should all have full battery voltage.

A little way down the red wire from where it connects to the battery junction block it should have a fusible link in the wire. See if it is blistered, hard - not flexible or discolored. It should be able to withstand a LIGHT pull on the wire.

If the problem is not at the battery junction block there is a connector that could have melted. This connector is under the dash, to the left of the steering column, by the Convenience Center. There are three wires in the connector – (red wire, light green wire, and Gray wire). There should be 4 connectors in the area where it is located. It is fairly high up in the dash.

[rm31859]

I have checked the fusible links and according to the wiring diagrams that I have looked at, the link for the A/C control unit is Blue. There are a couple of Blue links so I don't know which one is for the A/C. I also don't know what the rating on the links are. Any help? Thanks

[ChevyTech]

Disconnect the fusible links one by one to find out which one feeds power the the control head.

[rm31859]

Hi all, I found the problem. It's the 3 wire connector. But on my truck this connector is behind the glove box. It has a Red,Green and Gray wire. The Red is the battery feed coming from the Blue fusible link on the terminal block. As I tried to pull the connector apart I heard a pop and the control head lit up and the blower started working. It went back out as I was reinstalling the glove box so I'll have to go back in and see what the actual issue is. I may end up having to replace the connector but at least I know what the problem is. I want to thank all of you who have helped on this. It is very much appreciated.

[ChevyTech]

You're welcome!

Thanks for letting us know what you found.

Cut the wire on both sides of the connector and use a butt connector to splice the wire outside of the connector. The terminals have most likely overheated and melted the connector. You may not be able to unplug the connector.

Post a photo of the connector if you can. It will help people that find this thread with a search in the future.

[petee]

Love it when a 4.5 year old thread saves you a bunch of time. Checked the red wire at the control unit and I was only getting 10 volts. Looked behind the glove box and there was the the 3 wire connector completely melted.

[ChevyTech]

Originally Posted by petee

Love it when a 4.5 year old thread saves you a bunch of time. Checked the red wire at the control unit and I was only getting 10 volts. Looked behind the glove box and there was the the 3 wire connector completely melted.

It is nice to hear that people are using the search feature and making use of the information in old threads.

I am glad it helped you Petee!