[Richard and Rhonda]

Let me consult one of my AC books to see what they say is likely to cause what you are describing, which if I intepret correctly high side dropping with time, and also low side dropping with time. Do you have any idea what your starting pressures are, what they decay to, and how long that takes. Also what was the ambient temp when you took the readings.

What else is going on? Does it start out blowing cool air and then stop? If you put your hands on the expansion valve, does the outlet feel cold?

I am not sure what you are describing is an expansion valve problem. Here's why. If the valve were not restricting flow as it should then the low side would be higher than normal and the high side would be lower than normal. That is not what you are describing. In my way of thinking you are describing is a low charge. For example, it probably takes a good 4 or 5 minutes of running my AC for the low side pressure to drop to it's equilibrium point. It starts out around 40 lbs and gradually drops to 20 and stabilizes. In your case if the low side is in vacuum, then obviously there is nothing for the compressor to compress, so naturally the high side will not have a high pressure.

Does your system have a low pressure cut out switch? This switch is usually mounted on the low side just shy of the compressor inlet. It's purpose is to keep the compressor from running if the gas is too low. Running the compressor without gas burns it up. This switch will turn interrupt the power to the compressor clutch. Is your compressor actually turning when you see this? Obviously the pulley turns all the time the engine is turning, but is the center bolt turning? You have to look at that to see if the compressor is turning.

As far your specific question, I had higher than normal high side and lower than normal low side, so I figured the expansion valve could be partially occluded from fragments generated when my compressor cratered. So basically I was looking for physical evidence of a clot. Mine did have a little crud in it.

They are relatively cheap, it's the recharge and labor that gets you. You will find that one trip to an AC guy will pay for a decent set of gauges, a handbook, and a 30 lb tank of 134a at Sam's.

I'll PM you with my cell if I can.