AC Low Pressure switch failure?

[Pruittx2]

My system was down on freon, It looks as if the pressure switch on the accumulator has some seepage,,, any who, I drew down a vacuum and put 3 12oz cans in,,, after the first can,, the compressor kicked in and cycled fast,, till I put the 2nd can online, and pumped it in,, then the compressor ran full time that can was gone,, put in the third,, ahn the compressor, kicked out,, to not kick back on. Hmm,, I unpluged the switch on accumulator and ran a jumper wire, across the plug, compressor stayed on.
So, do I got something more, than that switch being bad,, or is it something else? I got the 3rd can in,, and at 65F my pressure was 35psi on the low side.

If I can throw any pics up to help,. let me know.

 

[94blazer]

If I recall correctly, the low pressure cutout is at the compressor, the switch at the dryer/accumulator is the high pressure cutoff.

Whats the high side reading?

 

[Acesneights1]

Sure it's not leaking out somehwere as fast as your putting it in ?
Just like a fatty .....look for the wetspot...:rofl:
I usually jump the low press switch to charge it. Faster.
Also I usually shut the vehichle off after the first can/lb whatever and check for leaks. Just because it held a vacuum doesn't mean there isn't a leak. In fact the vacuum can actually pull the leak closed alot of times until you re pressurize depending on what is leaking.

 

[Pruittx2]

Sorry I don't have a high side reading,, I just got the cheap gauge in the fill line thingy.
Only reads where it connects to system,, and that is the port on the line,, near the accumulator,,, Not the one by the compressor. Has a dial you set for ambient temp,, and then shows you where your pressure should be for that temp. It is holding fine and runs cold for a few minutes,, then when the compressor cyclces,, and goes off,, it won't come back on, , till you shut system down for a while or wait a few.

After looking up some info,, the switch on the accumulator is caller the AC clutch cycling switch.

 

[WarWagon]

If I recall correctly, the low pressure cutout is at the compressor, the switch at the dryer/accumulator is the high pressure cutoff.

Whats the high side reading?

Backwards. High pressure safety cutout is on the compressor. The low side switch is on the accumulator.

The switch on the accumulator is to keep the evaporator from freezing up by cycling the compressor clutch.

So 35 PSI R134a is 40 degrees - the range the switch should kick off the compressor. 3 cans is 2.25 LBS. What is the system capacity: 2.5 LBS or suburban with rear AC?

 

[THEFERMANATOR]

Low pressure switches on these trucks fail quite often as GM was stupid and let the switch carry the full current load that the A/C clutch draws instead of using the switch to control the compressor relay. I would say the low pressure switch is the #1 failure item for the A/C systems on these trucks. Also make sure the O-ring for it at the accumulator is good and the correct one. I've seen people install the wrong O-ring and it will let it leak out at the switch, or they won't replace the O-ring and it gets bound and tears and leaks or keeps the switch from fully seating and tripping the schrader valve. It should turn off at 20-22 PSI, and back on at 50-55 PSI low side pressure.

 

[Pruittx2]

My understanding, from other threads,, is that my xcab unit has a 2.5lbs capacity. I knew that 3 120z cans would fall a bit short. But it is cold at 65F ambient,, I'm seeing about 35-37F on the center dash vent. with engine at 2000 Rpms's.

Next question, then, is that Low Pressure switch on the accumulator changeable with out loosing my charge?

 

[vail426]

Yes. There is a shrader valve under the switch to keep it from leaking during replacement.

 

[Rodd]

My burb a/c is doing the same thing. W/ School, work, and kids I haven't had time to track it down. I'd better hurry before the hot summer days come.

 

[Pruittx2]

Ok,, So I replaced the compressor cycle switch on the Accumulator,, piece of cake,, and $9.99 at the zone. I also grabbed a 4th can of 134a and oil mix. Added 1/4 to 1/2 half of that can. With my high idle switch on 1050 or 1100rpm, it would get cold,, but after 7-8 mins the compressor kicked off, for 30-45 sec's then back on,, and it would continue to do that. I thinking it might still be a tad low.
But when I test drove it,, with t-stat in center vent, and 70-75F outside, it seemed to blow cold for the whole 12 min drive @ 55mph 38-40F cold. :smile5:
Temp on truck gauge would hit straight up at 210, then t-stat would open, and drop to 190 or so. I think this is about how it should be,, but just ask my wife, I've been wrong before!!!


Harbor Freight has the ac gauges for 59 normally but I got a coupon to make it $29. I really should go get them, But that's also a 40 min drive 1 way.

 

[Odlaw]

Backwards. High pressure safety cutout is on the compressor. The low side switch is on the accumulator.

The switch on the accumulator is to keep the evaporator from freezing up by cycling the compressor clutch.

So 35 PSI R134a is 40 degrees - the range the switch should kick off the compressor. 3 cans is 2.25 LBS. What is the system capacity: 2.5 LBS or suburban with rear AC?

x2

After replacing everything; compressor, evap, hoses, condenser and dryer, and new OEM low pressure switch, pulled vac overnight, no leaks - charged with Artic Chill.........one week later pressure switch took a dump - had to tap on it to get the compressor to cycle. I was not wanting to pull the refrigerant out and do all over again just to replace that stupid switch (mine does not have a schrader valve under it)- so, I just jumper ed the switch, put a digital thermometer in the duct and manually cycle the ac when the duct temp drops to around 32-36 F to keep her from freezing up.

 

[WarWagon]

Ok,, So I replaced the compressor cycle switch on the Accumulator,, piece of cake,, and $9.99 at the zone. I also grabbed a 4th can of 134a and oil mix. Added 1/4 to 1/2 half of that can. With my high idle switch on 1050 or 1100rpm, it would get cold,, but after 7-8 mins the compressor kicked off, for 30-45 sec's then back on,, and it would continue to do that. I thinking it might still be a tad low.
But when I test drove it,, with t-stat in center vent, and 70-75F outside, it seemed to blow cold for the whole 12 min drive @ 55mph 38-40F cold. :smile5:
Temp on truck gauge would hit straight up at 210, then t-stat would open, and drop to 190 or so. I think this is about how it should be,, but just ask my wife, I've been wrong before!!!


Harbor Freight has the ac gauges for 59 normally but I got a coupon to make it $29. I really should go get them, But that's also a 40 min drive 1 way.

If you are at the 2.5 LBS -+ 1/4 LB system charge you are ok. The compressor clutch WILL cycle. This is to prevent freeze up.

Have you fixed the leak? "pressure switch on the accumulator has some seepage" Freon leaves no trace, the AC oil does leave a residue.

Have you checked your fan clutch and cleaned the radiators? Cooling is often overlooked for AC repairs.

 

[Pruittx2]

Yep,,, new engine, 3 summers ago, with only 25,000 since. 21" composite fan HD fan clutch. New 180 (I think) t-stat. Had rad out and cleaned it then. Didn't hear fan kick in, at all yesterday.

I believe the leaks are fixed, as the only spot that was wet/dirty was at that switch. Once I charged it last spring, it was fine all summer, till the switch started acting up,, by then it was getting colder, and it went low over the winter.