Hi guys

Ambient today is 85F.

Got a weird one...A/C not blowing that cold, hooked up the gauges. Compressor would drop to 15psi low, 155psi high, then turns off, likely to avoid going into a vacuum. I added half a can of 134a, so now it was ~25psi low, 175psi high. I added another 1/3rd can, now the compressor won't engage at all. I have it on MAX A/C, coldest temp, max fan. Turned car on and off, clutch wouldnt engage.
...so I then removed a little refrigerant, and clutch cycles back on again and its working again, although still not that cold because it still reads as if there is not enough R134a in the system.

Is this an indication a sensor could be bad? What else would be stopping the compressor from engaging when I put in more refrigerant?
Any other ideas?

 

Sounds like its overcharged....are u using one of them el cheapo gauges? U need to have the system vacummed out then a proper charge .... my guess is those gauges u are using are Not very accurate.....

 

 

Just a heads up, MAX AC on any vehicle just closes the Fresh Air Vent in the cab or passenger area, nothing to do with the operation of an AC system

Ford doesn't have a different system, 134a, or any refrigeration system, all work pretty much the same way.

Compressor increases fluid pressure and heats it up.
Condenser allows any fluid that has vaporized during compression to turn back into a fluid.
The hot high pressure fluid goes thru an expansion valve which allows rapid pressure drop , and fluid COOLS rapidly
COLD fluid then goes thru Evaporator in the Cab, cooling any air passing thru the evaporator.
The now low pressure cold fluid goes back to compressor to start the journey all over again.

The low and high pressure switches are normally closed switches, usually the GROUND for the compressor's clutch runs thru them both, so if either of them OPEN compressor can not be engaged.

GROUND----------low switch-------------high switch-------------compressor clutch---12v
So even if compressor clutch gets 12volts it won't engage if there is no Ground, open switch

Chart here on pressure readings expected with outside temps: AC Pressure Chart | R-134a Temperature Pressure Chart


Yes it is possible your high pressure switch is bad, test with OHM Meter to be sure, 0 OHMS is closed, N/C, no change is OPEN

 

 

Replaced high presure switch and problem solved - It sucked in 12oz of r134a and compressor stayed on. Its 100F today and ended about 28psi low and 235psi high. I believe the system may have a leak, but those pressure will work for now and will see how long it holds the charge before I do a full vacuum and recharge based on weight.

 

Good work

Thanks for the update