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Phil
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I need help on an AIr Conditioning system please. I do think

Customer Question

HI, i need help on an AIr Conditioning system please. I do think I am paying monthly.
Submitted: 10 months ago.
Category: HVAC
Expert:  airheatman replied 10 months ago.

What problem are you having?

Customer: replied 10 months ago.
hi, 2011 New Holland tractor; ac compressor kicks in and out every 20 seconds; it is cold air but is this right ? Low side is 18-20 and high is 175.
Customer: replied 10 months ago.
It came is with the problem of "cycling" and not blowing cold air when it cycled. I recovered 2.3 lbs and then changed the "block valve" now is cycling every 20 seconds.
Customer: replied 10 months ago.
Is there any "corelation" between the low side pressure and the evaporator temp ? Someone has told be that 20lbs on low side guage means 20 degrees in evaporator?
Expert:  airheatman replied 10 months ago.

1. Do you know if the system uses R-134A and what is outdoor temp?

Customer: replied 10 months ago.
My AC temp chart shows low side pressure should be 35-40 lbs at 80 degrees outside temp?
Customer: replied 10 months ago.
134a
Expert:  airheatman replied 10 months ago.

Sounds like you probably have a restriction or blockage in the orifice tube or expansion valve

Expert:  airheatman replied 10 months ago.

The low suction pressure indicates the refrigerant is not properly getting back to the compressor so low pressure switch is shutting it off

Customer: replied 10 months ago.
I did just replace it. What should the low side be ?
Customer: replied 10 months ago.
Its not the temp switch in the evaporator thats shutting it off?
Expert:  airheatman replied 10 months ago.

At 80 degree ambient, we really should be running 40 to 50

Customer: replied 10 months ago.
I agree
Expert:  airheatman replied 10 months ago.

Manufacturer could have used a temp or a pressure switch but they are in direct corolation . A 20psig is about a 20 degree coil which would ice

Expert:  airheatman replied 10 months ago.

Did compressor fail and you had to replace?

Customer: replied 10 months ago.
No nothing failed: came in shop with low-low side pressure and frequent cycling-same as now.
Customer: replied 10 months ago.
It has an "electric thermostat switch" and I think it is shutting off compressure because it is getting too cold?
Expert:  airheatman replied 10 months ago.

Honestly to me it sounds like there may be a small particle or something moving around in the system that is causing it .You might try adding just a bit of refrigerant just to make sure it is not due to low charge.We can be up as high as 210 on high side.

Customer: replied 10 months ago.
Hi- just to follow up on this-my low side is running 18-20 lbs; the dealership said this is "normal"; so why does everyone else say the low side is 35-45 ? I don't get it? And there is just one pressure switch and its on the dryer.
Expert:  airheatman replied 10 months ago.

What does dealership say would cause the unit to cycle like it is?

Customer: replied 10 months ago.
I'm asking you
Expert:  airheatman replied 10 months ago.

Short cycling is usually caused by the pressure or temperature dropping below the pressures shown on the chart I sent. This would be anywhere below a 32 degree coil.

I can not answer why the dealership would say 18-20 is normal