I am in the midst of recharging my 1999 Jimmy, pretty much same as Blazer,
A/C has not run for years. Manifold gauges read empty. Pull vacuum for 1 hour, pretty close to 30 in/MG. Held that for over an hour, needle did not move. Hooked up 134a can to service line. Started engine, turned on A/C switch. Opened low side valve, compressor would not come on. Jumped low pressure switch. Compressor came on, but does not seem to suck 134a from can. High and low pressures are ths same about 65psi. What do you think?

 

Anybody have an idea?

 

Might be a missing orifice or a bad compressor. Even without an orifice I would think the pressures would show a slight change with the compressor cycling. With engine off, try turning the compressor by hand, you can do this with the belt on just turn the front of the clutch. Do you feel any resistance?

 

*Created its own thread*

 

The cycling switch on the accumulator turns the compressor on if/when pressure is above ~42psi. At 65psi on the low side, the compressor should have come on without jumpering the connector.

If the can of refrigerant was ~65F, low side pressure would indicate ~65psi. It's possible the valve in the service port did not depress and allow the refrigerant into the system. If that's the case, the only pressure on the manifold would be what's in the service hose, up to the service port. How many CFM is your evacuator pump? How long did it take to draw vacuum down to 29.4"? (29.4" is the maximum vacuum that can be achieved...two atmospheres).

 

How about we push the two shraders, have a dead {14.7-14.7=0} system. Put the gages on, crank her up, jump the clutch and if no high low or almost, then dead compressor.