Compressor won’t stay running.

[Dgreen]

I replaced a leaking service port on a 2003 Chevy truck yesterday. Compressor wouldn’t run when I tried to charge it. Several times it engaged for a split second then quit. Checked fuses and relays, tapped the clutch, jumped the low pressure switch, and disconnected the battery in an effort to maybe reset something. The few times it tried to run seemed to be related disconnecting and reconnecting the battery.

[JohnHere]

It's possible that your manifold gauge hook-ups aren't depressing the port's Shrader valves, which will prevent refrigerant from entering the system. If you have the type of connectors with the small blue and red thumb-wheels, ensure that they're rotated all the way CLOCKWISE after connecting them to the system to fully open the Shrader valves.

[Cusser]

It's possible that your manifold gauge hook-ups aren't depressing the port's Shrader valves, which will prevent refrigerant from entering the system. If you have the type of connectors with the small blue and red thumb-wheels, ensure that they're rotated all the way CLOCKWISE after connecting them to the system to fully open the Shrader valves.

I had similar with gauge fitting not seating well on my 1994 Suburban which was R134a. I had to hold the fitting on tight to depress the valve.

[Dgreen]

I was able to pull a good vacuum. (480 microns) I was pulling vacuum from the low side and had the micron gage on the high side conneeection. System took in some refrigerant. I thought jumping the low pressure switch would make the compressor run even if the system was empty?

[JohnHere]

I'm assuming it's a full-size Chevy pickup. If so, the specs I have list 26 ounces of R-134a and 8 ounces of PAG 46.

When you say it took "some" refrigerant, how much exactly and how are you trying to charging it...small cans or 30-pound cylinder? By weight or by pressures only? Are your refrigerant container(s) empty or nearly so? Is your refrigerant container's valve fully open? Is your low-side hand-wheel open?

Sounds silly, I know. But sometimes we overlook the obvious things.

[Dgreen]

It is a full size truck. I was charging from a 12oz can and valves were all the way open. The can as getting when I first opened the valves. The truck wasn’t running. I’m assuming it took two or three ounces.

[JohnHere]

You should charge refrigerant gas (can upright) into the low side (only) with the engine running at about 1,800 RPM, the A/C on, and the blower on medium speed. The low-side handwheel on the manifold gauge set must be open and the high-side handwheel must be closed.

With the engine and A/C off, the pressure in the system will quickly equalize to the can pressure, resulting in just a few ounces of refrigerant going in. With the system running as described above, the low-side system pressure will drop below the can's pressure and allow the refrigerant to be drawn in.

I suspect that's the problem.

[Dgreen]

After pulling a vacuum, I open low side and let the system draw in as much refrigerant as it can before I start the engine. That is enough to get the system to start short cycling on ccot system and it eventually takes the measured charge. The compressor on this one just won’t run. The clutch would engage for just a split second a few time and that was after reconnecting the battery. I suspect an electrical problem somewhere. I’ve never ran into this before.

[JohnHere]

Sounds like your charging procedure is okay since you eventually got a full charge in. Another thought: Do you have steady voltage (around 14 volts) at the compressor with the system turned on? If so, then the clutch is suspect. If not, the A/C amplifier could be bad.

[Dgreen]

I didn’t get a full charge in it. Voltage at compressor seems to me intermittent.

I’m not familiar with ac amplifier.