I have a 2005 Silverado Ltz ext cab 1500 problem is when I stop or truck sitting it will not blow cold air it has the digital temp control set to 60 which is the lowest setting air blowing out around 75 on warmer days but when driving down the road it's blowing 38 then stop for traffic it's back up to 75 again I have replaced the condenser blew all the a.c. lines out replaced the compressor and accumulator the fans come on when a.c. is turned on have plenty of sweat on the accumulator any help would be appreciated

 

-vehicle in park...rev the engine up to 2500 rpm and hold it there for 30 seconds... does the a/c go cold?

-is there good air flow through the radiator...the fan must pull air through the rad to get air thru the condeser. Are all the fan shrouds in place...missing or out of place shrouds reduce the fans ability to move air through the condenser.

-there was a tsb for faulty low pressure cut off switchs- does it seem like the system is turning off the compressor when the vehicle is stationary?

-what method did you use to fill the system? How much pag oil was added?
-do you have gauges to check hi and low side pressures?

 

Yes good air flow thru the radiator has dual fans in good shape had it filled with r 12 and pag oil at a shop to factory specs and it does get colder but not as cold as it does driving down the road put the gauges on yesterday running 30 lo side and around 160 hi side the compressor will not cut off when idling just stays on the whole time not sure about the pressure switch I haven't changed it yet I was thinking maybe the a.c. controls or the air sensor aspriator may be bad not sure tbough

 

what about the rpm test?
r-12 is the wrong refrigerant...do you mean r134a?

 

Yes sorry r134a and it gets a little bit cooler but not as cold as driving it will go down to around 60° at 2500rpm

 

I put a thermator in vent idol is around 70 reved to 2500 rpm around 60 and driving with no stops it's around 45

 

ok, the rpm test is a quick test for the compressor. results not conclusive. did the old compressor seize up and fill the orifice screen with metal?

when you checked your high and low side pressures...what were the relative humidity and ambient temps. I will refer to an a/c performance chart.

 

No actually the old compressor was fine that was the advice I got from a local shop as to the problem a weak compressor I changed that the condenser and accumulator and new orfice tube as for outside temps was last summer around 95 and humidity probably around 20 or 30% I've owned the truck 3 years last summer when I couldn't take the heat anymore put those parts on and same results not really wanting to take it back to another shop

 

I checked the a/c performance test for this model year with electric cooling fans
ambient temp 95 and rh 25% says:
low psi 52
high psi 234
max discharge temp 63*F
if the numbers you gave me are correct...when both hi and low psi are low...first thing to check is low refrigerant level

 

Low refrigerant level.

Was going to say weak fan clutch, but sounds like you've got electric fans.