Dieselguy123

I know this an old thread but ...
I'm trying a fixed temp capillary tube type switch in the suction well on my 91 1st gen.
Haven't had time to thoroughly check it out yet. I have a feeling its not going to get cold enough there to cycle. I measured the switching temp of this one at just a hair be!ow 32.
I'll probably have to buy an adjustable one to make it work.
Does anyone know where you can get access to the evaporator fins if I need to place the probe there ?
So has anyone had success with the rotary adjustable capillary switch's in the suction well ?

j_martin

It should work if the sensor has good contact with the evaporator tubing.

Dieselguy123

Tried the switch. Evap still freezing up. Guess the probe is not getting cold enough to cycle. Either not making good enough contact or needs more heatsink compound in there.
There is the possibility that this switch is calibrated for evap fin insertion.
I ordered another switch with adjustment shaft. I'll try that next.

Dieselguy123

Well got the capillary switch with adjustment ****. Greased the probe up good with silicone grease and stuffed it Into the return line well. Had to adjust it quite a bit warmer than the initial setting but its cycling now.
There are more of these available on eBay. Mine was $7 shipped. Part number SW6490C

Jim Lane

I have installed a thermostatic switch on my air conditioner, the same units that I have used on a lot of the ARA, evaporators and Kysor roof mounted air units.

I mounted the control under the edge of the dash and the capillary tube is inserted the fins of the evaporator in the upper right side, since I have an access opening into the air box to clean it, I kept it high so it would not be in the way.

I drilled a small hole through the case and inserted it into the fins, I also soldered a small blue LED and dropping resistor in series to indicate when the current was on, now a glance at the floor will tell me if the compressor is cycling by the bright blue dot on the passenger side.

The calibration between the suction well and the evaporator fins would be different.

I should be able to get some new pictures up soon.
The SW6490 is a commonly used thermostatic switch.

Jim

edwinsmith

I hate blue LED's.

Jim Lane

Edwin,
I use a blue led to indicate it is a cold circuit, red would be for heat,
Same way the spectrum goes from IR to UV.

Did you have a bad experience with the color blue as a child? lol

Incidentally Rebecca was blue when she was born, amazing what a little oxygen will do

edwinsmith

Whenever I see blue LED's in signs or on electronic equipment it hurts my eyes. It defracts more than red and green and causes fringe effects. Besides, Red LED's were first.

mknittle

Ah yes kelvin color temperature.

edwinsmith

Actually blue is at the hotter end of the spectrum.

mknittle

that's right, I haven't thought about it for a while.

Jim Lane

Blue definitely grabs your eyes for attention, it has a dazzling effect,
Like the police car behind you with his light bar strobing.

edwinsmith

I think blue gets through the black diesel smoke better.

Chevjerico

Hey all, found this thread while trying to troubleshoot why my AC evaporator freezes up. After about 45 minutes of freeway driving. This was last year on a 100 plus day. This is on my 93 D250. I'm not an AC guy but a pretty good backyard mechanic. I noticed my compressor runs continuous so I purchased a low pressure cutoff switch thinking this was the problem. Then I noticed the harness has been shorted as described above. Is the evap freezing a normal thing with this kind of mod?

spoonhonda

Yes. If you do The mod that you quoted here it will run The compressor continuously and freeze up your evaporator

The low pressure cutoff switch is only to protect the compressor in the case that most or all the freon (and oil) leaked out.