Engine Size: 6 cyl.
Refrigerant Type: 134
Ambient Temp: 80
Pressure Low: 40
Pressure High: 200
Country of Origin: United States
I am a HVAC Contractor and work on residential and
commercial units, but I am trying to fix my own car.
I have a Toyota Sienna 2005 6 cylinder.
The ac works great if you don't go out for a drive.
The car at idle will operate great. But as soon as you
take the car out on the road and get it up to 40-50 miles
per hour, the low side pressure drops to 20-25 psi and the
compressor stops. I think the evaporator is icing up and the
compressor won't come back up until the evap thaws out.
My first thought would be clutch gap, the first time the evaporator gets cold enough to cycle the compressor off normally, it fails to re-engage. Low side of 20-25 is right where you want it in a TXV system on the highway.
You can test this theory by idling the car with A/C on for a while until everything under the hood is good and hot, then turn the A/C off and back on and see if it restarts like it should.
Edited: Fri September 21, 2012 at 11:45 AM by mk378
Have you pulled the charge and weighed in the exact amount? I'm not in the office to check the control type but you may also have a out of range evap sensor. To verify MK's theoty, place a small lamp across the compressor leads and see if the lamp stays lit. If the lamp (or voltmeter) drops out when the problem occurs, investigate the control for the compressor.
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