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low static, high low and high high R12

Leggie on Sun July 14, 2013 11:37 AM User is offline

Year: 92
Make: Mazda
Model: MPV
Engine Size: ?
Refrigerant Type: 12
Ambient Temp: 70F
Pressure Low: 60
Pressure High: 250

I came across an R12 Mazda MPV with complaint of poor cooling. The owner states it cools, but not very well.
Refrigerant flow can be observed in sight glass and it is foamy.

I'm only seeing about 40 psi equalized pressure in the system and this in itself tells me that system does not have enough refrigerant to keep the saturated pressure or that there is but its trapped somewhere. So switched off, I observed 40 psi on both sides.

With the system on and revved to 1500 RPM, I'm observing 60/250. I don't get it. Static is clearly too low, yet I'm seeing signs of refrigerant activity like sight glass activity and pressure on both sides is too high, especially on low side.

Any idea?

94RX-7 on Sun July 14, 2013 12:22 PM User is offline

First thing I'd look for is proper condenser airflow. I'm sure there's a billion miles of bugs and rocks and smashed fins in the condenser if it is the original. Condenser/radiator fans working ok?

mk378 on Sun July 14, 2013 12:31 PM User is offline

If you have liquid refrigerant but the static pressure isn't right, the only possible conclusion is that the substance in the system is not pure R-12.

Leggie on Sun July 14, 2013 4:10 PM User is offline

That was one of those things on my list.
Speaking of such, do you know if something like this is attachment activated or pressure activated? Older R12 cylinders do not have a check valve so I'd like something that can be put in line to protect the contents in case of a mishap by a tech, such as hooking into a system that presents higher pressure than tank on low side or accidentally opening the manifold on high side while charging.

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