AC Controls Fan not working on Hi

[east302]

The link to the 1997 PDFs isn’t on that first page of that thread - it’s in post #92. I think all of the years have been added by now, it’s just that no one can edit that first page to add the link.

88-98 Service Manuals

Some heroes don't wear capes. Thanks everyone.

www.gmt400.com

 

[HoffmansHaven]

The link to the 1997 PDFs isn’t on that first page of that thread - it’s in post #92. I think all of the years have been added by now, it’s just that no one can edit that first page to add the link.

88-98 Service Manuals

Some heroes don't wear capes. Thanks everyone.

www.gmt400.com

Wow! Thank you! I found it. It never occurred to me to keep going through the thread. I probably won't dig through my truck again until fall. It's getting too hot here to mess with it. I have a lot of books now to help me.

 

[obs_dude-tx]

I experienced this same problem on the wife’s Suburban the last few weeks. I followed the wiring diagram provided on a previous post and got the test light out. My problem was the electrical connection after the firewall before the relay. There is a post in this forum that provides a step by step troubleshooting from the service manual that will help you narrow down the power issue with a test lamp.

 

[blutge]

Hello All, new here. I have issues with my 1990 Chevy C1500 4.3L 2D HVAC system. There is a history, but cut to the chase and this is the current issue, the blower RUNS HIGH when turned On. Set the controller to Lo and Med, it run the same, HIGH SPEED. When switched to High the blower turns off. The resistor runs glow red hot, If the high blower relay is removed (purple wire) then the blower speed is low, resistor doesn't glow, but the same thing happens on the Lo, Med, switch settings, same speed no change, set on High the blower shuts off. The AC compressor, AC High, AC Low switches under the hood are NOT connected. Is this a short in the wire harness, a control panel short/burn out, or one of the three Blend Door Actuators. I've replace the wire harness from the pigtail plug, relays, and resistor. Looked at the back of the control panel it looked fine no carbon burn, did not look at the chip board yet, the actuator by the driver's side leg is working. Not sure about the other two, would faulty actuator cause this? Any help would be grateful, trying to get this fixed before finishing the R-12a to R134a AC upgrade. Thank You, B PS: the one fuse in the fuse box is good.

 

[AK49BWL]

Hello All, new here. I have issues with my 1990 Chevy C1500 4.3L 2D HVAC system. There is a history, but cut to the chase and this is the current issue, the blower RUNS HIGH when turned On. Set the controller to Lo and Med, it run the same, HIGH SPEED. When switched to High the blower turns off. The resistor runs glow red hot, If the high blower relay is removed (purple wire) then the blower speed is low, resistor doesn't glow, but the same thing happens on the Lo, Med, switch settings, same speed no change, set on High the blower shuts off. The AC compressor, AC High, AC Low switches under the hood are NOT connected. Is this a short in the wire harness, a control panel short/burn out, or one of the three Blend Door Actuators. I've replace the wire harness from the pigtail plug, relays, and resistor. Looked at the back of the control panel it looked fine no carbon burn, did not look at the chip board yet, the actuator by the driver's side leg is working. Not sure about the other two, would faulty actuator cause this? Any help would be grateful, trying to get this fixed before finishing the R-12a to R134a AC upgrade. Thank You, B PS: the one fuse in the fuse box is good.

Actuators will NOT cause this issue. Have you replaced ANY of the relays? Switched connectors to the relays, see if the problem changes? It sounds like you might have a failed high-blower relay.

Relay positions per speed:
SPEED Relay 1 || Relay 2
Off: OFF OFF --> Power in to relay 1, out to relay 2, dead ends at relay 2 because relay 2 is off.
Low: ON ON -->Power in to relay 1, out to resistor pack, current flows through both resistors directly to blower - relay 2 is unused.
Med: ON OFF --> Power in to relay 1, out to resistor pack, current flows through ONE resistor and then to relay 2, from relay 2 to blower.
High: OFF ON --> Power in to relay 1, out to relay 2, from relay 2 direct to blower.

So if Relay 2 isn't working, you'll have the same speed on Low and Med, nothing on High, and removing the relay entirely from the circuit causes the system to go to low speed because relay 2 (in its default off state) allows current to bypass the second resistor. The resistor glows because there's 1: no airflow over it, and 2: With relay 2 off, current is flowing through the one resistor - Low and Med are not running the blower at max, but technically Med.

For future reference, it's better to create a new thread for your problem

 

[obsraulito]

I had the same problem... turned AC to the first three speeds and it would work fine but as soon as it was switched to HI it would just shut off. i replaced the blower, the relay behind the glove compartment, the resistor and the whole control/switch panel and the issue continued, I finally started checking the fuses under the hood and noticed the 50 amp fuse labeled AC was melted at the fuse box and the wire and fuse were not even making contact as soon as i touched them my high speed came on. so is that fuse only for the AC high speed?

 

[Cesar97ykn]

I have a 1997 K1500. When you turn the fan to Hi it stops. It works in Lo, 2, and 3 but as soon as you hit Hi it just stops. Here is what I did. I tested everything and checked fuses. Didn't really find anything so I went to the parts store and bought new everything except the control. New fan, relay, resister and put all that in and still the same thing. I then took out the control and I noticed when I took one of the plugs off there is nothing for it to "plug" to. The controls in my truck were replaced at some point. Part number on it says 09378815. It was manufactured in Mexico on 9Apr of 2018. It didn't come in the truck. I wonder if it's the correct one for this truck. There are 3 harnesses that plug onto it. There is a large one with 6 wires and a ground it's rectangular and goes into the big connector towards the center. There is another long skinny plug that connects on the side. Lastly there is a smaller one on the other side with a smaller 4 pin connector. That's the one just going onto a piece of plastic. There's no metal tabs or anything that plugs into it. I think that's my problem. That smaller 4 pin has the purple wire that goes down to the fan on it too. I have no idea how this thing is even working. Has anyone ever examined these to any detail. Why would mine be like this? I noticed that on the long skinny connector it is just connecting to a ribbon on there. I tried to look up inside that the white housing of the control to see the smaller connector I am talking about might be something like that but I can't see anything in there. Is there a way to take that apart to look inside without destroying it? I know this is a long winded post but I want to fix this someday. Does anyone know if there are any diagrams with enough detail that would show what that supposed to be? Thank you.

Picture added for clarity.

@HoffmansHaven for months I was struggling to solve the same issue that you are experiencing on my 97 2dr Yukon. I just fixed it today! Check the red wire on the hardness near the blower motor, mine was melted/burnt. I replaced a new plug and it solved it.

 

[Cesar97ykn]

@HoffmansHaven for months I was struggling to solve the same issue that you are experiencing on my 97 2dr Yukon. I just fixed it today! Check the red wire on the hardness near the blower motor, mine was melted/burnt. I replaced a new plug and it solved it.