Around 3 Ohms is a fine ground, so no problem there. By the way, ground for relay socket 4 comes from the ECU. You may want to repeat the 3&4 voltage test to rule out user error.

Was the cabin blower on high during this test?

And the static pressure seems too low. What is the outside temp where you are? For example, static pressure should be 88 psi at 80F (after high and low sides have equalized).

 

Blower AC set to max fan speed. It's 75-80 here today. What would cause the low side to go into vacuum though. Should I toss in a can of freon?

So does the ECU shut power off on accelleraton?

 

The readings are confusing and inconsistent with the fact that the A/C blows cold. First, the static pressure reading is too low. Were the low and high sides equalized? You need a manifold gauge set to sort this out. Vacuum could indicate moisture in the system or a bad expansion valve.

No. But a tripped A/C pressure switch or thermostat would.

 

So I just added 9oz of freon and it does not go into vacuum anymore but drops to about 5-10# as the engine rpm rises. It seems to be cooler than before but I'm going to have to check the expansion valve in a few days and see if its getting frosty. Where is that thing anyway?

Update: I turned off the engine and let the car stabilize for an hour. The static reading is now 105#. When I started the engine the low side dropped to 25# at idle and cycled normally with the fans on/off.

 

Stop adding refrigerant without readings from a manifold gauge set. You have no idea how much refrigerant is already in system or whether there is air in there. Can't help you if you ignore advice.

 

Those gauges built into the charging hose are accurate to about plus or minus 50 psi. Worthless.

If it gets cold once, you have enough refrigerant in the system. Either there is enough to make cold air, or there isn't. There aren't gremlins under the hood adding and removing it as you go down the road.

There is no pressure switch or control on the low pressure side. So watching only the low side pressure trying to think of why the compressor shuts down abnormally (if it even does) is useless.

Only high side pressure can cut off the compressor. The switch there is designed to be closed under all normal operating conditions (pressure from 50 to 400 psi). Normal compressor cycling is controlled by evaporator temperature.

 

I think I'm using a fairly reliable gauge.

There must be a low side switch to keep the compressor from running when empty.

 

The high side switch has dual action, it is what will prevent the compressor from running when empty. It will be able to run with a very low charge though, which overheats the compressor, thus the use of a compressor thermal switch. There is no pressure switch on the low side.