AC and Heater Control Problem

I have a 91 Silverado k1500. It has the push button AC and heater control panel. The panel does not function - no fan - no heat - no air - no lights in the panel. The part number label is no longer on the panel but it is the style with the "RECIR" button rather than the "MAX" button (part # 16204785).


I installed a used 16204785 (Max button style) and found the same results. No function - no lights in the panel. I am told the replacement panel was tested aand worked.

There is current showing at some of the connector points on the truck side connector plug.

I have cleaned the connector points on the back of the panel and in the plug connection.

I have checked the fusable links near the fire wall and all seem fine.

I have checked the fuses under the dash and all are fine.

There are three relays behind the glove box. I think one or more have something to do with the AC. I have heard buzzing from these relays in the past but this has gone away. The panel did not work at all before or after the buzzing problem.

Any suggestions?

Thank you
JBB

No A/C panel lights means you're not getting power. Since you know you have 12V at the connector and you cleaned the contacts, the question is are the connections actually contacting? If the connector terminals got hot from a malfunctioning relay, then they may have become soft enough to not spring back. I'd also look at the relays to see if they have clean contacts. If they're oxidized, they can become hot and lose their pliability.

You can try to bend/pinch the terminals inside the connector to get them to contact the panel's pins.

Thank you for your reply. For the benefit of others who may be following this or may havve a similar problem...

The terminals in the plug seem clean and tight. There are actually 12 individual connection points in the plug and on the back of the control panel. If I recall correctly, I found voltage at 2 or 3 point. It seems logical that the panel should at least light up. I suspect that there must be some other point in the contacts that should be hot when the key is on or perhaps when the light switch is in the on position.

I did unplug all three relays. Connections were tight and clean.

From this point, I think I will attempt to trace each wire back from the plug looking for problems. One of these wires should be a ground. Since I have no function at all, that could be the single item preventing all else from funtioning.

Chime in if you think my though process is incorrect or if you might be able to provide additional assistance. Can teh relays be tested at a dealer or auto parts store???

Thank you
JBB

It could certainly be a bad ground connection. A decent Haynes manual should have a circuit diagram to help you with the A/C panel.

I have finally had some time to work on my problem but I have made no progress. I simply have no heat or ac. No lights or function at the electronic control panel. No functioning of the AC, no blower - nothing.

I have gone through the wiring from the control panel plug back toward the passenger side to the blower box and fire wall and did not see any problems. I unwrapped the bundled wires and all looked good.

There are three relays behind the glove box. There is power on various wires goinging into the relays. I have swapped the connections between all three with no change. Is it possible that one or more bad relays would create a situation like I have?

I pulled the resistor out - looks fine - zero ohms when checked on either side of the resistor.. There is no power at all going into the resistor - key on, key off, lights on, lights off.

There is a splice in the wiring harness with 2 browns, 1 gray and 1 black going toward the drivers side. These 4 wires lead into a plug connection that is white and gray. I separated this plug and found one prong on the drivres side showing power. I presume these 4 wires go off to the ignition switch and light switch. Should more that one of these have current with the ignition on or off or with the lights on or off?

I am thinking about taking this to the shop but I can only imagine many hours of diagnostic time ticking away at $60 per hour.

Any and all help will be greatly appreciated.

JBB

There appears to be a fusible link that supplies power to the relay switches and the control unit...look for a red wire from the control head and trace it back to find the link. This circuit is supposed to be hot at all times, so be careful.

The dash fuse will supply power to the relay resistors, but not the adjoining switches. The link allows the necessary current to run the blower. Hope this helps!

So the red wire at the control head is supposed to be hot at all times? I have power at some of the dozen or so wires at the control but I do not recall if red was one - i think not. This is great information - thank you. It gives me something concrete to work from. I do not see any fusible links under the dash so I would think that the corresponding link would be at the junction block on the drivers side of the fire wall. The red and a hundred other wires exit the cabin on the passenger side - low on the firewall. By sight and touch, all of the links in this area seem fine. I'll check with a meter. Thx JBB

Welp, I saw a fusible link on the Autozone wiring diagram, but don't see one in my Haynes book. I find it hard to believe that there wouldn't be some sort of in-line fuse for the blower, control head, et al. My book shows the wire coming straight from the battery junction block (drivers side near the firewall I think). But the red wire I can see might be a larger gauge than the others since it powers the blower, thus easy to spot...but no guarantee.