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A/C Thermostat Control Switch

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tomj View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tomj Quote  Post ReplyReply Direct Link To This Post Posted: Aug/01/2020 at 11:59pm
I wouldn't worry about exact calibration, a go/no-go test with ice should be sufficient. What Heavy sez. If you can make the switch open/close with ice it's working.
1961 roadster american, 195.6 OHV, T5
1968 american, 199ci, T14
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Post Options Post Options   Thanks (0) Thanks(0)   Quote george w Quote  Post ReplyReply Direct Link To This Post Posted: Aug/02/2020 at 6:22am
I believe the disc you're referring to is actually a rotary on/off switch. When the control knob is fully CCW it disconnects the power from the switch, otherwise the rotary temperature controlled thermal switch would always have power going to it. This means depending on ambient temperature the compressor clutch could engage and the blower would be running at low speed all the time the ignition switch is on.

There should be a little "calibration" type set screw on the body of the thermal switch. This screw will allow you to tweak the temperature of the on/off point for the compressor. Normally you don't need to mess with this but if you find the temperature control knob's operating range does not seem to be "centered" then you can adjust this set screw to alter the on/off trip point.

Edited by george w - Aug/02/2020 at 6:30am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jsejamx Quote  Post ReplyReply Direct Link To This Post Posted: Aug/02/2020 at 7:19am
Nothing in the area of the disc or the disk itself rotates as you turn the shaft.  I can see the cam plate which moves the lever on the switch as you rotate the knob (the rotary switch portion) and its not part of this stuff.The insulator board, copper ring, compression spring, etc. all have clearance for the threaded tube which attaches the switch to the Weather Eye bezel.  The insulator board itself is riveted to the switch body.
 
I looked at the wiring harness for the A/C and there is a 2 spade connector and a male pig tail that go to this switch.  It all looks original (no splices) so I'm pretty sure this is the OEM switch.  I'm going to try to find the harness diagram to determine if it's a ground or not.
 
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george w View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote george w Quote  Post ReplyReply Direct Link To This Post Posted: Aug/02/2020 at 8:07am
It's been a long time since I've been under my dash but I believe either that disc is supposed to turn or there's a moveable contact that moves around that disc. There should be an OFF detent felt as the shaft is rotated fully CCW. When fully CCW there should be no power going to the thermostatic switch ( which cycles the compressor ) or out of the short pigtail that goes to the blower speed switch. That pigtail wire is not a ground. It feeds battery power to the low speed side of the blower control switch to automatically activate the lowest speed of the blower motor as soon as the a/c system temp control is moved off the OFF detent.
Long time AMC fan. Ambassador 343, AMX 390, Hornet 360, Spirit 304 and Javelin 390. All but javelin bought new.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jsejamx Quote  Post ReplyReply Direct Link To This Post Posted: Aug/02/2020 at 11:50am
George W.
Thanks for the explanation , it works exactly as you mentioned and helped me locate the problem.  The rivets which hold the insulator board to the switch body pulled out about a 1/16 of an inch.  The compression spring pushed the whole thing forward which disengaged the ring from the short flat on the shaft.  I pulled the board off, removed the rivets, re-oriented things and then squeezed it back together and sure enough the ring does turn when you turn the knob.  Not much design margin there!
Anyway, thanks again.  Onward to trying to fix the other problem.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote george w Quote  Post ReplyReply Direct Link To This Post Posted: Aug/02/2020 at 6:56pm
With old cars it's always something ! Glad to be of help.
Long time AMC fan. Ambassador 343, AMX 390, Hornet 360, Spirit 304 and Javelin 390. All but javelin bought new.
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