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skwoodwiva
03-23-2019, 12:47 AM
This condition of poor set point control is a plague of all vehicles I have owned.
Why we get no control is baffling.


Accustat AS-90, any .25 of so fuse holder.

Or a Honeywell th1010d2000 also good only for 1 amp. This not my choice as I will reserve it for my heater & is for you to test. In battery mode it should work, being a relay stat & not a SS relay, but it may not for 12v even though I see no reason it should not. I like the simple operation of the former. You may have to play w/ the installer setup to get a similar cycle rate.

Find the blue/green stripe 18 ga or so wire coming out of the plug somewhat behind the AC on / off button.
This wire energizes the compr clutch.

It is ~ a 2.1amp or so duty. The stat is good for 1.2 amps max.
So you need a helper relay NO contacts to make the blue wire and let the stat make the relay coil. Which can go in the area behind the switch as well. I took power from the cigarette lighter with common blue squeeze take off jacks.

There you go, perfect AC control for your tin.

Midwestdrifter
03-23-2019, 02:08 AM
You will wear out and kill your compressor early by using the clutch to control temperature. The system uses an expansion valve to keep the temperature of the evaporator around 40F. Then hot air is mixed in to the flow by the ATC to produce the desired temperature. the system is not designed to cycle the clutch except when switching on/off and during under temp and overpressure.

skwoodwiva
03-23-2019, 02:21 AM
You will wear out and kill your compressor early by using the clutch to control temperature. The system uses an expansion valve to keep the temperature of the evaporator around 40F. Then hot air is mixed in to the flow by the ATC to produce the desired temperature. the system is not designed to cycle the clutch except when switching on/off and during under temper and overpressure.

So the Super Heat is too high? Is there an accumlator? Is the metering device a TXV? So I may need to add a desuperheating bypass of some kind. Hmm I may add a discharge temp sensor to override the stat.

I do run the condenser fan whenever the AC is on even if compr is off. I will be putting a TC bead on the discharge line to monitor

Midwestdrifter
03-23-2019, 02:23 AM
The control is a TXV, there is an accumulator/dryer. You can read the evaporator temperature using a suitable scanner. Generally it's maintained between about 35 and 45. The temperature setting on the Dial will control how much hot air is mixed in to maintain the cabin temperature. The ATC Monitors the highside pressure with a sensor and will disable the compressor on high or low pressure.

A failed TXV or off charge can cause weird behavior.

Aqua Puttana
03-23-2019, 04:35 PM
The temperature knob control is a potentiometer. It can get wonky and affect the heating cycles. Maybe that applies to A/C also. This is easy to try.

The potentiometer contacts may have a bit of corrosion.

Try twisting the knob with a bunch of gentle, but quick twist motions.

You don't want to jam stop to stop and maybe break something.

Move the knob away from the stop, give a bunch of short twists back and forth, index a bit further, give a bunch of short twists, etc. until the entire range of motion has been done.

The idea is that the quick twists will help the potentiometer wiper to rub itself clean. If it doesn't work you haven't lost anything. (As long as you don't break it.)

:cheers: vic