My suburban, which is a 1997 2500 with a 454, is having a strange A/C issue. The system is good and holds freon and gets very cold as long as you are moving. I narrowed it to the aux fan not coming on. I pulled the grill to check out the fan. I put power to it and it comes on and sounds fine. So I am not getting a signal to it. I started testing the various switches and relays that are A/C related and couldn't find where the signal comes from that goes to the fan relay. Anyway, I then get back in the truck to put it up for the night and the A/C controller has freaked out on me. When the fan speed switch is in the off position the compressor clicks on, but of course there is no fan on in that position. As soon as I turn it on the compressor turns off and the A/C button light goes out. Like it is backwards all of a sudden. Could I have cooked it by putting a test light on one of the switches or relay? Do you guys think it is the controller itself or possibly something else? The last thing I checked before it went bonkers was the high pressure cut out switch on the back of the compressor (the one that is held in with a snap ring). Help!!!!!

 

Anyone, anyone?

 

I'm still thinking.
It sounds like you've got some wires reversed but that doesn't seem likely. I would have to go back through everything that had been done and double check my work. Could a wire been removed and put back on a wrong terminal? The test light should not have caused any harm unless something go shorted out. I'm stumped for now. If anything comes to mind, I'll pass it on. Good luck.

 

There are two fuses used in the HVAC blower circuits: A 30amp fuse in the Underhood Bussed Electrical Center, (UBEC) and a 20amp fuse in the Instrument Panel, (IP) fuse block, always check them first.

The HVAC blower motor is mounted in the HVAC housing, under the hood on the passenger side, near the hood hinge. There are 2 wires connected to the blower motor. The purple wire comes from the blower relay. The black wire must have less than 5 ohms resistance to ground. Using a fused jumper wire, apply battery voltage to the purple wire. The blower motor should operate at high speed. If not, the blower motor is faulty.

The blower motor resistor is usually mounted near the blower motor in the HVAC housing with only the connector visible. The three lowest speeds go through the resistor. The electrical connector has 4 wires. To check the circuits from the blower switch, unplug the connector from the resistor. Turn the ignition switch to the RUN position, and the HVAC mode switch to the HEAT position. Use a volt/ohm meter or test light to check each circuit.

The brown wire should have battery voltage when the blower switch is in the low position.

The tan wire should have battery voltage when the blower switch is in the medium 1 position.

The light blue wire should have battery voltage when the blower switch is in the medium 2 position.

The dark blue wire goes to the blower relay and should have less than 5 ohms resistance to the terminal in the blower relay connector. Reconnect the blower resistor connector. If any of these tests fail, either the blower switch or the associated wiring is faulty.

The blower motor relay is usually located near the blower motor resistor, either attached to the HVAC housing or to the firewall. It is about 1 inch cubed in size. All blower speed circuits go through the blower relay. The 3 lower speeds use one circuit, and high speed uses a separate circuit within the relay. The electrical connector has 5 wires. To check the circuits, unplug the connector from the relay. Turn the ignition switch to the RUN position, and the HVAC mode switch to the HEAT position. Use a volt/ohm meter to check each circuit. The larger orange wire, (from the UBEC) should have battery voltage at all times.

The smaller orange wire, (from the blower switch fed by the IP fuse) should have battery voltage when the blower switch is in the HIGH position only.

The purple wire goes to the blower motor and must be less than 5 ohms resistance to the terminal at the blower motor connector.

The black wire must have less than 5 ohms resistance to ground.

If all of these tests pass, the relay is faulty.

The dark blue wire comes from the blower resistor and voltage will vary depending on the blower speed setting. Low speed should read the lowest voltage, and increase with medium 1, and medium 2. If voltage is not present on one or more blower speed settings, the resistor is faulty. Reconnect the blower relay connector.

 

Thanks brother, I just printed that out and am going to see what I come up with. I may take the controller out of my 1995 and swap it into the Suburban even though the 95 doesn't have the rear defrost option I am fairly certain it will work everything else.

 

glad i could help

 

Well a little progress...and thanks again to Viper for the PM and getting me off my @ss today to go do some more checking. I tested the A/C controller wiring specifically the harness that goes to the Off/Fan speed switch and it has power coming in, but sends power to the compressor (green wire) when it is in the off position. There was no fan at any speed until I accidentally discovered if you put pressure against the back of the switch you can make the blower fan kick in and out. I am not sure if I could have caused this by testing one of the switches/relays because it was working fine until I started testing it. My original problem was the cooling fan and then this thing totally grenaded. I am hoping that somehow the issues are related and a new controller will resolve the cooling fan as well as the blower fan. I ordered a controller on eBay today so now the waiting game begins. I will let you know what comes of it. Thanks again Viper!

 

No problem anytime

 

put it on a switch. its a rig but will work

 

OK, I got the new A/C controller today and that was part of my problem. The A/C now blows out of the vents like it should and the compressor comes on when it should. It did not solve the fan issue. I did a little more digging and found that the fan is it turned on by a relay that is grounded by a switch that is screwed into the high pressure side right on top of the compressor. I think that switch is bad b/c I have ground to one side, but not the other when the system is turned on. The only reason I am not 100% is the system has lost a full charge (yeah it has started to be a domino effect). The compressor body itself is leaking. I bought this truck over the winter so this is my first go round with the A/C system. I bit the bullet today and bought a new compressor, accumulator and orfice tube which will get installed tomorrow along with a good flush and some new o-rings. Hopefully this will be the end of my A/C woes in the toy hauler!!!!!