How do you test the rear expansion valve on a ford 350 super duty van?

Answer 1

Put some dry ice on the control bulb. It should shut the valve and the low pressure gauge will go down into the negative. I assume you have a set of test gauges for air conditioning and have some mechanical skill. You can see how the expansion valve is in line and has a small copper line coming off of it that senses temperature. Dry ice melts at -20 or so, so it is cold enough to completely shut an expansion valve. If it shuts, it means that the gas is still in the bulb and tube, and that the valve is not stuck. Look somewhere else for your problem once this has been eliminated.