You can use an infrared thermometer to get some ideas what's going on. Typically the condenser should be 20-30* hotter than ambient temperature, and warmer at the top than the bottom. Low side pressure roughly correlates with evaporator temperature, on these trucks add +5* maybe.
My old '94 was ice cold except when idling hot in traffic. I replaced the fan clutch with a Hayden heavy duty, installed an '05-ish full circle fan- but no matter what I did there was some crossover between the system shutting down from overpressure and the fan clutch kicking in. Never got it right.
Enter the new '94 I'm just finishing up- everything new in the A/C including the evaporator. It had the factory Hayden condenser still in it, about 1-1/4" thick. I got to thinking, and looking at the '95 next to it, that maybe the condenser I put in it just wasn't up to *****. I did a bunch of homework and ordered a condenser from Original Air- https://www.originalair.com/90-93-c...ban-truck-condenser-orifice-tube-style-11-248 because it has more tubes than anything else I could find, is a parallel flow condenser, and is about 5/8" thick, better than generic auto parts units. Only thing is it's -93, so it doesn't have the port for the aux condenser fan pressure sender. With the factory 6.5 diesel fan and clutch, it idles hot in my driveway at about 120* condenser temp on recirc and ~125* on free air. Never threatens to overheat and so far traffic testing holds up. So the short story is I believe that these trucks (specifically those with R4 compressors) just need more condenser than the aftermarket provides. So for testing, IR the cold line coming from the accumulator, should be +35*. The low pressure cutoff is about 25psi, so below freezing. The condenser on my other truck, the not-good one would kill the compressor at about 155*.
My old '94 was ice cold except when idling hot in traffic. I replaced the fan clutch with a Hayden heavy duty, installed an '05-ish full circle fan- but no matter what I did there was some crossover between the system shutting down from overpressure and the fan clutch kicking in. Never got it right.
Enter the new '94 I'm just finishing up- everything new in the A/C including the evaporator. It had the factory Hayden condenser still in it, about 1-1/4" thick. I got to thinking, and looking at the '95 next to it, that maybe the condenser I put in it just wasn't up to *****. I did a bunch of homework and ordered a condenser from Original Air- https://www.originalair.com/90-93-c...ban-truck-condenser-orifice-tube-style-11-248 because it has more tubes than anything else I could find, is a parallel flow condenser, and is about 5/8" thick, better than generic auto parts units. Only thing is it's -93, so it doesn't have the port for the aux condenser fan pressure sender. With the factory 6.5 diesel fan and clutch, it idles hot in my driveway at about 120* condenser temp on recirc and ~125* on free air. Never threatens to overheat and so far traffic testing holds up. So the short story is I believe that these trucks (specifically those with R4 compressors) just need more condenser than the aftermarket provides. So for testing, IR the cold line coming from the accumulator, should be +35*. The low pressure cutoff is about 25psi, so below freezing. The condenser on my other truck, the not-good one would kill the compressor at about 155*.