AC temp up and down

[Racegas]

Recently replaced hose and drier. Recharged system. AC will blow ice cold, then air becomes cool, then ice cold again, cool, ice cold. Bad switch?

[FSJunkie]

On the older systems like ours, the compressor cycles to maintain evaporator core temperature within a certain range. As the evaporator cools, the compressor cycles off, as it warms up, the compressor cycles back on. There will be a change in outlet air termperature as the system cycles on and off. The termperature switch that controls compressor cycling has a long copper capillary tube that sticks into the evaporator coils. It is very important that the tip of the tube sticks directly into the dead center of the evaporator and that some length of the tube loops around the end coils.

If that doesn't do the trick, then the switch is probably bad. It has what is called a "historisis effect", which is the buffer zone it gives between on and off. The size of this zone will affect the termperature change in the outlet air as the compressor cycles. be warned, you don't want the compressor cycling on and off too much, it's not good for the clutch.

[babywag]

On later model '86-up there is a small module under the dash mounted to the rear of the driver's side ductwork.
This module controls cycling of the compressor.
If this module is bad it may cause this issue.

The thermistor may also be bad and can be tested.
Spec chart is in the MR253 manual.

I'd start with the module.

[Spirit_of_61]

On later model '86-up there is a small module under the dash mounted to the rear of the driver's side ductwork.
This module controls cycling of the compressor.
If this module is bad it may cause this issue.

The thermistor may also be bad and can be tested.
Spec chart is in the MR253 manual.

I'd start with the module.

You have been talking about FSJ ac for a long time evidently. Have you been able to get yours to work? Have you found a thermistor replacement?

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[Utahbroker]

I am in same boat. Located replacement module (EBay) now need replacement thermistor. Unable to locate a thermistor for 86 JGW

[89_Wagon]

My 89 will cycle on/off on every setting except max AC. It seems that's the way these FSJs control temp. I always had it on max AC and until this spring and I too thought my AC broke. I experienced that cold then cool then cold cycling every minute or so. There's no fresh air mix in these systems so on/off is the only way to control temp.

Does this happen on max AC?

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[candymancan]

Like he said. On max a.c it wont cycle on and off.. only if you turn the temp up closer to middle will it do that.

Temps can also chabge based on driving. Sitting in traffic or at a light itll be warmer. When you move itll get colder again due to the condensor getting more air from moving.