Low side retard / high side zero & compressor not kicking on

[bigjoncoop]

I'm trying to fix my brother's ac in his 98 Silverado and the ac compressor is not kicking on. I put gauges on it and the low side is pegged on the gauge reading retard and the highside is reading zero.

Would this cause the compressor not to kick on?
Whats the next step to determine if the high or low side psi is causing the compressor not to engage?

The truck had major work done to it so I have no idea of they had to disconnect ac line etc....

Or should I vacuum the system and start from scratch?

[tbirdtbird]

How much AC experience do you have? **EDIT: to fix an error**
What is your ambient?
The low side being at retard means it is at 120 or more, hi side of zero suggests the coupler is not making full engagement with the port, or perhaps the hi and lo hoses are switched somehow.

Did the AC work before the shop did the repair?

For starters, check fuses and relays and try your gauge set on a known good car and tell us the readings at 1500-1800 RPM doors open, recirc on, max fan , max cool, and provide ambient. That way we can test the integrity of the gauge set. Is it a loaner from a parts store? Those take quite a beating

We need to trouble shoot before you vac and add refrigerant....else you may end up right where you are now.

[JohnHere]

By major work, do you mean bodywork? If so, was it hit in the front?

[JohnHere]

I'm trying to fix my brother's ac in his 98 Silverado and the ac compressor is not kicking on. I put gauges on it and the low side is pegged on the gauge reading retard and the highside is reading zero.

Your red and blue hoses might be switched at the Manifold Gauge Set as already suggested. Double-check for that and correct, if necessary.

If indeed the high-side gauge is indicating approximately 120 PSI and the low-side gauge is indicating zero (static pressures), then it sounds like the system has a blockage someplace, which could be at the orifice tube or another location.

If you have no measurable pressure for whatever reason on the low-side of the system, the compressor will not engage.