Air Conditioner Issue

[ksbillsfan]

AC on a 1978 Traveler doesn't work. Had it checked out and was told there was no power going to the compressor. The system holds freon and is full. I can turn the switches on the unit in the cab and can get the fan to blow air. From a schematic I found online, looks like the line that powers the compressor runs from the unit in the cab to a thermostat then to the compressor. Where is the thermostat located? What could be causing the power not getting to the compessor? Thanks in advance.

[Dennis Bernth]

If the fan works, you have power to the switches. The fan switch jumpers power to the temp switch right next to it, likely the temp switch is bad or has a bad spot on it. Did you try turning the temp switch to a different position? Sometimes you can clean them up and make them work with 'contact and relay cleaner', other times they just need to be replaced, they've lived their useful life.

[ksbillsfan]

Ya, I have turned the temp switch from max to min, no effect. How would I clean the switch? Pop it off? Or do I need to figure out how to take the unit apart? Thanks

[Dennis Bernth]

Originally Posted by ksbillsfan

Ya, I have turned the temp switch from max to min, no effect. How would I clean the switch? Pop it off? Or do I need to figure out how to take the unit apart? Thanks

You have to take the air duct apart to access the switches. Not a huge job, pretty straightforward, and it'll give you a chance to mess around a little in there (carefully!) with a test light to make sure the juice is going where it needs to go. When you're doing electrical work on these beasts, purchase #1 should be a decent test light. They always seem to come with a blunter tip than will penetrate wire if needed, so I touch it up on the bench grinder and go. I like the bigger ones from Harbor Freight with the coil cord, I probably have four or five of them around the shop so I can always find one when I need it.

[ian choplin]

The thermostat switch is located on the passenger side of the a/c assembly. This is where the evaporator is. I don't think you can get to it without evacuating your system.

Ian

[ksbillsfan]

Ok, I'm not real mechanical when it comes to cars. I'll see if I can figure out how to get to the switches. Thanks guys.

[Dennis Bernth]

Originally Posted by ian choplin

The thermostat switch is located on the passenger side of the a/c assembly. This is where the evaporator is. I don't think you can get to it without evacuating your system.

Ian

I think you're talking about the expansion valve on the evaporator; that doesn't wire into the electrical system that activates the compressor, it's what controls the flow of refrigerant to keep the evaporator from freezing up. The switch in the under dash panel has a wire coming out of it that runs to the compressor to control the on/off action of the compressor.

[fredsterra]

like Dennis said. The fan switch sends power to the temp. control switch. From there to the thermostat in the evaporator.

The fan switches are bad about getting dead spots to send power to the temp.

One thing I did was installed a tiny LED in the panel so it would light up when the thermostat sends power to the clutch. It's pretty handy to see if it's in a "dead spot" so I can move the blower up or down just a tick to make sure it's not in a dead spot.

I haven't decided on the switch yet. But I am planning on using a lighted switch to send power to the temp. control. And bypass the blower switch to the temp. control.

I will spilt the hot feed one to the blower and one to the new switch.

[ian choplin]

I was referring to the switch inside the evap case with the probe that goes into the fins of the evaporator. I figured this was the "thermostat."

Ian

[fredsterra]

The Blower switch also sends power to the temp. control switch. The knob to the right of the blower. Then it sends power to the Thermostat switch with the lead in the evap. That sends power to the comp. clutch.

But the blower switches are bad about getting dead spots that send power to the temp. control.

Make sure your getting power to the temp. control switch, then to the thermostat. The thermostat switch is a major pain to replace. So check the easy first. You can remove the blower duct the check them.