A/C quits when on Highway

[Sam Davis]

My A/C works well at Idle, but when I get on the highway at 70MPH it will cut off, it is nice and cold at about 40MPH but get on the HWY and it quits????

Any Ideas????

 

[theamcguy]

Your A/C is not cycling. The A/C is designed to cycle on and off to prevent the evaporator from freezing solid. What is happening is the evaporator is freezing solid and air won't pass through it you feel the warm air, the ice melts then you get cold air again. There should be a cycling switch that is pretty easy to change out.

 

[crash68]

The AC cycling to keep the evaporator from freezing is only part of issue. Chances are there is an issue with the refrigerant charge or a problem with the compressor itself. Without knowing the running pressures and temperatures, saying that it's the pressure switch premature.

 

[theamcguy]

In my experience A/C repairs fall into 2 categories $50 or $2000+. If turning off the A/C on the highway waiting 15 to 20 min and then turning it on and the A/C is now cooling chances are it is the pressure switch. $50 repair. If not then it is the $2000 repair.

 

[Sam Davis]

Put a set of gauges on it LOW side 36 HIGH side 38 will freeze you out at idle, no cycle on the clutch, but when you increase the RPM it will Cycle on and off, replaced the high and low pressure switches no change, Run down the Highway 70 MPH and it will quite working, I did find that the relay was overheating, replaced it, the compressor came back on, but still cycles if the RPMS are above idle???

 

[crash68]

There is a problem with the High side reading 38 psi. Depending on where in the system the High side port is, it's probably a restriction.

 

[Sam Davis]

got some help on how to use the ac gauges,, low side 20, high side 200,

 

[ZHowell]

My A/C does the same when I get up to about 2500 RPMs but it doesn’t quit if I put it on max ac it stops blowing the all my vents and just blows through windshield