Heater Control/AC Question

[wwotr]

Attached picture of a Heater Control exactly like mine.

I know the Blower Positions (Fan Speed) are as follows:
Furthest Position Up is---Off
Next Position down is ---Low Speed
Middle Position is---Medium Speed
Furthest Down Position is---High Speed

In turning on my AC today it was more like this (below):
Furthest Position Up is---Off
Next Position down is ---Low Speed
Middle Position is---Medium Speed
Furthest Down Position is---Low Speed**


The Heater Control is Brand New as is the AC Compressor, so is it some type
of a relay problem, or would it be more likley the Fan going out?

Thoughts/Suggestions/Comments are always welcome.

[ls1nova71]

Double posr

[ls1nova71]

Sounds like the high fan relay isn't working, it's on the heater box next to the right kick panel. Check to make sure the ground to it is tight, the relay screws into the box and sometimes the will come loose and cause the ground wire not to be tight on the relay. Also check the heavy guage orange wire that powers it for power (the fuse or where that wire plugs into the fuse box, sometimes you'll get a bad connection there) and if that checks out I would replace the relay. Switches also go bad, but usually when there's no high it's the relay. Also while you're checking things, make sure your connection of the plug is good at the switch. They will become loose over time and when they get loose the build up alot of heat and will melt the connectors.

Also it could be the resistors in the heater box, but let's hope not because they're a sob to get to.
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[1972RedNeck]

I have the same trouble. I have checked all of the plug-ins and wires. I have also replaced the relay. I just bought a new resistor to install but haven't done it yet as

Originally Posted by ls1nova71

Also it could be the resistors in the heater box, but let's hope not because they're a sob to get to.
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My question is: would a bad resistor make high speed not work?

[ls1nova71]

High speed is controlled by the relay. It gets it's power from the fuse box, its a heavy gauage orange wire, check that.
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[mrein3]

Originally Posted by 1972RedNeck

I have the same trouble. I have checked all of the plug-ins and wires. I have also replaced the relay. I just bought a new resistor to install but haven't done it yet as
My question is: would a bad resistor make high speed not work?

No. High speed goes around the resistors.

[mrein3]

Originally Posted by wwotr

Attached picture of a Heater Control exactly like mine.

I know the Blower Positions (Fan Speed) are as follows:
Furthest Position Up is---Off
Next Position down is ---Low Speed
Middle Position is---Medium Speed
Furthest Down Position is---High Speed

In turning on my AC today it was more like this (below):
Furthest Position Up is---Off
Next Position down is ---Low Speed
Middle Position is---Medium Speed
Furthest Down Position is---Low Speed**


The Heater Control is Brand New as is the AC Compressor, so is it some type
of a relay problem, or would it be more likley the Fan going out?

Thoughts/Suggestions/Comments are always welcome.

Your fan is fine. You have wiring issues.
When I converted my non-AC truck to AC, I was getting the same speeds you're seeing. On the used parts I bought the plastic plug that plugs into the back of the fan switch was melted. On ALL the used ones I came across the plug was melted.

Check that first. If you have two wires crossing on the plug you get all kinds of funny wiring issues.

If the plastic plug is fine and all the wires behind there are touching the correct connection and only the correct connection behind the switch I'd be highly suspect of your high-speed fan relay.

You're going to need the color coded wiring diagram that somebody posted on here, a multi-meter, and some time and patience. I wish that colored diagram was available when I went through my fan wiring. I had to use the b&w diagrams in the service manual.

The low and medium speeds are made low and medium by passing 12 volts through a resistor block buried behind the glove box. If memory serves one speed is 3 volts and the other is 6. Or maybe it is 6 and 9 volts. Either way the voltage is stepped down by wasting it through those resistors. To get high speed 12 volts travels through the switch to a relay again buried behind the glove box.

It has been a while so I don't remember exactly on my truck but on my Chevelles I know there is a fuse holder in the wiring loom that goes across the firewall above the transmission. That 20 amp fuse in there is for the high speed fan. Look for that and check it. Follow the wire back from the fan to locate it.

[wwotr]

Originally Posted by mrein3

Your fan is fine. You have wiring issues.
When I converted my non-AC truck to AC, I was getting the same speeds you're seeing. On the used parts I bought the plastic plug that plugs into the back of the fan switch was melted. On ALL the used ones I came across the plug was melted.

Check that first. If you have two wires crossing on the plug you get all kinds of funny wiring issues.

If the plastic plug is fine and all the wires behind there are touching the correct connection and only the correct connection behind the switch I'd be highly suspect of your high-speed fan relay.

You're going to need the color coded wiring diagram that somebody posted on here, a multi-meter, and some time and patience. I wish that colored diagram was available when I went through my fan wiring. I had to use the b&w diagrams in the service manual.

The low and medium speeds are made low and medium by passing 12 volts through a resistor block buried behind the glove box. If memory serves one speed is 3 volts and the other is 6. Or maybe it is 6 and 9 volts. Either way the voltage is stepped down by wasting it through those resistors. To get high speed 12 volts travels through the switch to a relay again buried behind the glove box.

It has been a while so I don't remember exactly on my truck but on my Chevelles I know there is a fuse holder in the wiring loom that goes across the firewall above the transmission. That 20 amp fuse in there is for the high speed fan. Look for that and check it. Follow the wire back from the fan to locate it.

This makes sence. I had my Truck at the Shop for Interior painting and they took everything out.
When I got it back home, the Blower worked but there was NO A/C. When I took it back, I was told ......
"A Jumper Wire Came Loose under the Dash".
Since I've had 7 operations within the last 3 years,
I'm unable to contort myself to get under the Dash,
but I will take this valuable information, BACK to my Mechanic.

As usual, you guys (and this Forum) RAWKS!!!!