LO Side 0 PSI/ Vacuum, HI Side 100 psi

[Andr3_153]

I have a 1999 Honda Accord, recently fixed an a/c compressor electrical issue and wanted to run the car and try it out. Had no cool air coming out only outside temp air. hooked up my gauges to see what was going on. While at idle and A/C compressor was running I had what appears to be 0 psi maybe even vacuum on my low side gauge and roughly 100 psi on my high side gauge (20-40psi on low side and 175-250 psi on high side normal operating range for reference obviously). Once I turned off the A/C the low side gauge jumped up to well over 200 psi and my High side drops to roughly 75-80 psi as well. Any help would be appreciated.

Amount of refrigerant in system is unknown because they charge and arm and a leg to remove and refill.

[JohnHere]

The first set of pressures with the engine at idle and the compressor running suggests a very low refrigerant charge, although to get meaningful pressure readings, the engine should be at about 1,800 RPM, A/C and blower on maximum, doors and windows open, and a known, full refrigerant charge in the system.

The second set of pressures with the A/C (and engine?) off doesn't make sense because you're measuring the static pressures, which should approximate the ambient temperature, with the high-side and low-side pressures being about the same. A low side of 200 PSI and above (and in the "retard" zone of the low-pressure gauge) and a high side of 75-80 PSI just isn't feasible.

Are you sure that your Manifold Gauge Set is working properly and is hooked up correctly? Also, what was the electrical issue you worked on?

[atikovi]

While at idle and A/C compressor was running I had what appears to be 0 psi maybe even vacuum on my low side gauge

Isn't there a low pressure switch that cuts off the compressor below about 20 psi? Did you hotwire the compressor to run all the time?

[JohnHere]

If I recall correctly, this Honda has a trinary switch on the high side of the system that allows the compressor to run (or prevents it from running) according to factory-set high-and-low pressure limits. The switch also controls the electric condenser fan(s) in much the same way but according to a different set of high-and-low pressure limits on the high side. I don't believe this vehicle has a switch on the low-pressure side of the system.