91 E150 4.9L V6 with dealer installed A/C

Converted from R12 to R134A several years ago. System has low pressure port at receiver drier but no high pressure port. Every year I add a can of R134A and system works fine for a year. I finally got a set of gauges to check system pressure. Does anyone know what the following pressures should be:

1) Pressure at low port with engine running and a/c off
2) Pressure at low port with engine running, a/c on and compressor engaged
3) Pressure at low port with engine running, a/c on at moment compressor cycles off.

Thanks

 

1) Pressure at low port with engine running and a/c off:
Ambiant Air Temp.(F) Low Side Pressure(psi)
50- 45
55- 51
60- 57
65- 64
70- 71
75- 78
80- 86
85- 95
90- 104
95- 114

2) Pressure at low port with engine running, a/c on and compressor engaged:
40-45
3) Pressure at low port with engine running, a/c on at moment compressor cycles off:
Should not happen but the Low side cutout switch should be set to open (stop the compressor) at 24 PSI and will let the compressor restart at 43.5 PSI.

 

Thanks subford

For #1, left column is temp and right column is psi, is that right.

 

Yes that is right.

 

Compressor was cycling off as you said, as pressure dropped to about
24 PSI and turned on again when pressure built up. Added one more can of 134A and nice cool air constantly. Thanks again