AC doesn't blow on high

[Drizan]

Hey All,
Back with a new AC problem on my 79 El Camino. The other day I started up my car and the AC was set on high (AZ summer) and it didn't turn on. I then switched it down to medium and it blows fine. So it works on all of the other settings from low to medium. Just not the high which is super weird to me since it is so much more common to hear about a car ONLY blowing on high. Even googling the issue just leads me to people with that problem rather than mine. I recently (couple months ago) cleaned up the console and regreased everything but I did it again without any change. I changed the fuse and it is the same thing. I ordered some new fuses as the fuse I replaced it with is an unknown age just sitting around in my box of fuses and it really feels like maybe a fuse issue but that is a couple days out and only a sort of...wishful thinking.

Any ideas?

 

[LeftLaneOnly]

I believe there are different wiring/ one for high speed AC using inside cabin air and one for low/medium using outside air
Does the high speed work with only the heat on?

 

[ELCAM]

Two things to test.

Power for the high speed comes from the second number two circuit red fuseable link, the low speeds come from the first fuseable link to the fusebox to the HVAC control to the resistor block.

High speed uses a relay, when it is not in high a normally closed terminal is connected to the output of the resistor block allowing those voltages to run the blower motor. When in high the relay is energized and gets power from the second number two red circuit.

See if there is +12V at the 12 gauge red wire at the relay, if not likely the fuseable link is bad if there is +12V at the red wire the relay is the most likely suspect. With the key on and the HVAC control on high fan the orange wire at the relay should also have +12V if it does it is the relay at fault. If no +12V at the orange wire it is the switch on the HAVC control that is bad.

 

[Drizan]

I believe there are different wiring/ one for high speed AC using inside cabin air and one for low/medium using outside air
Does the high speed work with only the heat on?

No it does not. Only runs on medium and low on heat as well.

 

[Drizan]

Two things to test.

Power for the high speed comes from the second number two circuit red fuseable link, the low speeds come from the first fuseable link to the fusebox to the HVAC control to the resistor block.

High speed uses a relay, when it is not in high a normally closed terminal is connected to the output of the resistor block allowing those voltages to run the blower motor. When in high the relay is energized and gets power from the second number two red circuit.

See if there is +12V at the 12 gauge red wire at the relay, if not likely the fuseable link is bad if there is +12V at the red wire the relay is the most likely suspect. With the key on and the HVAC control on high fan the orange wire at the relay should also have +12V if it does it is the relay at fault. If no +12V at the orange wire it is the switch on the HAVC control that is bad.



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Thank you. I will give that a shot and once I have tested it I will post again. Thanks for the diagram.

 

[maxi426]

Check for burned red wire connection at C127

 

[olds307 and 403]

Check for burned red wire connection at C127

Exactly, one of the many burnt wires on my 88 Cutlass.

 

[Drizan]

Two things to test.

Power for the high speed comes from the second number two circuit red fuseable link, the low speeds come from the first fuseable link to the fusebox to the HVAC control to the resistor block.

High speed uses a relay, when it is not in high a normally closed terminal is connected to the output of the resistor block allowing those voltages to run the blower motor. When in high the relay is energized and gets power from the second number two red circuit.

See if there is +12V at the 12 gauge red wire at the relay, if not likely the fuseable link is bad if there is +12V at the red wire the relay is the most likely suspect. With the key on and the HVAC control on high fan the orange wire at the relay should also have +12V if it does it is the relay at fault. If no +12V at the orange wire it is the switch on the HAVC control that is bad.



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Sorry it took so long for an update. Couldn't find my voltage meter. Anyway the switch and relay are both solid. The red wire running into the relay is not getting any power so it seems it is going to be the fusable link. I can see on my book diagram that the fusable link is connected to that red wire but I am not 100% sure where it is in the car as my wires are still in the black wire organizers and I don't want to pull all my wires to chase the area down if I can help it. I mean I will but if anyone knows the actual location that would be great. Thanks.

 

[pagrunt]

Sorry it took so long for an update. Couldn't find my voltage meter. Anyway the switch and relay are both solid. The red wire running into the relay is not getting any power so it seems it is going to be the fusable link. I can see on my book diagram that the fusable link is connected to that red wire but I am not 100% sure where it is in the car as my wires are still in the black wire organizers and I don't want to pull all my wires to chase the area down if I can help it. I mean I will but if anyone knows the actual location that would be great. Thanks.

I may have a idea of what could be wrong here. You're getting power for everything but the high speed relay so this be an issue from the splice in the harness where that feed & the two alternator wires, the ignition BAT2 & BAT3 wires & the non-lighting power feed wire meet with the feed off the starter. I'm thinking it has a break or cut between there & the relay. As brought up by maxi426, check the 4 wire connector fron the engine harness to the heater-A/C harness for a burns/melted plastic (has the red with light green, dark green & may have a black ground) which is a common GM design fail. A fix is to find where it still has power & splice in a 30 amp fuse like GM did up to the mid '70's to protect the feed.

 

[69hurstolds]

In case you need a new connector. These things tend to melt. Semi-common problem culprit when hi speed fan doesn't work. This is like the original style, but you could use a weatherpack type if you wish. This is much cheaper usually.

DELPHI PACKARD GM 56 SERIES FOUR CONDUCTOR CONNECTOR SET 16-14 GA. | eBay

All components to make one each 56 series assembles.

www.ebay.com