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Adjusting the high Pressure switch on A/C

katugly

katugly

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Does any one know what way turns the cutoff up or down? Where should it be set for R134A? I cleaned out my whole system yesterday put in a new dryer, adjusting orfice tube and the oil. Im about to go vacc it down to spec for a hour. I wanted to know if that switch needs adjusting for R134A
 
uummmmmm...NO.


I have never seen a HPCO on a factory auto A/C.

If it's running high head....adjusting the switch is not your answer...
Correct the head pressure issue.
 
I thought you needed to change the switch out when you went from r12 to r134 :confused: because they run at different pressures
 
huh....I have been out of the auto A/C field for a while.....


a quick search came up with this..

http://www.familycar.com/store/?Ntt=mercury+Array+a%2Fc+cut+out+switch&oes=true

apparently some cars do have them.....:wink1:

I guess if you change refrigerants,, you would have to change the switch...they don't appear to be adjustable..just a fixed range of pressure.

I quit messing with auto air a long time ago..The ones I work with now look like this..

http://cgproducts.johnsoncontrols.com/CAT_PDF/1900171.pdf
 
Pressure switches aren't adjustable....atleast I've never seen one.

The high pressure switch doesn't care what type refrigerant. All it does is shut down the compressor if the pressure reaches a certain point. The MRAP's run R134a and the HP switches are set to cut out at ~400psi. R12 and R134a may have different working pressures, but a cut off pressure is a cutt of pressure, regardless the type of refrigerant.

If you were talkin the difference between R134a and say....507c, that's a different story all together.
 
The high side switch is usually non-adjustable and it's only job is to protect the system and avoid venting through the over-pressure valve.

The low side pressure switches ARE adjustable and that's the one you want to adjust. Yes, the stock switches on the receiver/dryer can be adjusted. Just pull the connector off and you will see a little screw slot up in it. I can't tell you the right pressure without looking it up. Usually the gauge has both temp and pressure on it. Adjust the switch until it cycles off just as the temp comes to the freezing point of water.
 
Blue85 said:
The high side switch is usually non-adjustable and it's only job is to protect the system and avoid venting through the over-pressure valve.

The low side pressure switches ARE adjustable and that's the one you want to adjust. Yes, the stock switches on the receiver/dryer can be adjusted. Just pull the connector off and you will see a little screw slot up in it. I can't tell you the right pressure without looking it up. Usually the gauge has both temp and pressure on it. Adjust the switch until it cycles off just as the temp comes to the freezing point of water.
Click to expand...


That is what I was looking for I guess I should have said the low pressure switch that cuts the compressor when it sees high system pressure. Think its the standard screw out for decrease and in for increase?
 
katugly said:
That is what I was looking for I guess I should have said the low pressure switch that cuts the compressor when it sees high system pressure. Think its the standard screw out for decrease and in for increase?
Click to expand...
The high pressure switch cuts the compressor when it sees high pressure. The stock R-12 systems did not have this switch. It is recommended, but not required, to add it when converting to R-134. It's job is basically to prevent venting refrigerant.

The low pressure switch is the one that needs tweaking when you change the refrigerant. It cuts the compressor when the low side pressure is too low. This is part of normal operation for regulating the refrigerant flow and temperature in the evaporator. It needs adjustment because R-12 and R-134 have slightly different temperature/pressure curves.

At the same low side pressure, R-134 is a little warmer than R-12.

I don't remember which way you need to adjust. Hook up the gauges (even a single gauge on the low side will work) and as you plug the connector back on to the switch, note the temp/pressure where the compressor turns off. Don't mess with it if you don't have the gauges. An A/C shop might hook up theirs and let you do the adjustment for a few bucks.
 
Ok did some asking around at my dads shop and its screw in for colder and out for warmer. screw it in and it keeps the low pressure thresh hold lower. Screw it out and it raises the low pressure threshold. Basiclly if its not freezing up and the compressor is running don't fudge with it. Uploaded a couple of pics for people who dont know what adjustment I am talking about.

DSC03659.JPG

DSC03661.JPG
 
katugly said:
Ok did some asking around at my dads shop and its screw in for colder and out for warmer. screw it in and it keeps the low pressure thresh hold lower. Screw it out and it raises the low pressure threshold.
Click to expand...
I believe this description is backwards. In adjusting mine yesterday, it was clear that "in" (clockwise) is raising the temp/pressure set-point. I know this is an old thread, but all still relevant.
 
Fwiw

I.) unplug the switch

2) look inside, if there is a screw that's your adjuster.

Done 2 or 3 134a conversions that way.
 
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