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Low side pressure too low at 40-50 MPH

jvel2012 on Fri September 21, 2012 12:56 AM User is offlineView users profile

Year: 2005
Make: Toyota
Model: Sienna
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.

mk378 on Fri September 21, 2012 11:43 AM User is offline

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

Dougflas on Fri September 21, 2012 1:10 PM User is offline

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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