W900a a/c upgrades

Have you resealed all your ducting?

 

And manual water valves on the engine? I would lean toward the condenser before the compressor. Reason being your truck came with R12 and is now running R134A which requires a little higher capacity condenser. Many vehicles had large enough capacity condensers to still function well but at least some Mack's and White GMC's did not. I never had that problem with a KW but yours has had an extra evaporator installed and the condenser may be under sized for that.
The rotary units are surly better or the world would not be going to them. However I must ask if you have not seen many trucks with a cab and sleeper units that worked well with a piston compressor.
And of course make sure everything else correct, cores and radiator are clear etc.

 

Never seen that before. Condensor on my '80 W900A was roof mounted. I always assumed that was how they all were.

 

Never had a problem with these big grill condensers but not many of them were ever here. Some trucks are very particular to freon amount and there is no exact amount printed for 12 units converted to 134 I have ever seen. I do it this way. Start with about 2 LB freon in the system, a/c compressor straight wired, fan clutch running all the time or a big shop fan pushed up in front of the radiator. Set on fresh air with the doors open system on high, thermo in vent. Add freon 4 oz. at a time and wait about 5 minutes. continue intell you it gets no colder and you are done. Some times you can gain 10 degrees this way. Radiator core really really clean and seal between sides of radiator and hood? I do not remember how they sealed together.

 

My Freightliner has a York Compressor and cools excellent. I replaced the York last year and after the radiator shop recharged the system it was pretty weak. Mid 50's! Talked to radiator shop and they suggested cleaning the condenser and evaporator. Sounds like your condenser has to be clean externally, I wonder about the inside. I'm not a mechanic, I am a parts changer. Anyway I got coil cleaner at the hdw. store and cleaned both components on the outside. I swung the condenser away from the radiator and blew it out. A lot of stuff came out. I cleaned the evaporator as best I could in the truck. Tooth brush, shop vac. and air plus the coil cleaner. It was pretty plugged up. I was not totally happy with the evaporator job, but I did not want to evac the system and pull it out. Anyway after the clean-up job the system is down to 45*. Harbor freight has the thermometers. I would like to get a good Red Dot thermos. though. Good luck!

 

All of these suggestions to me are sensible. Ditto on the York compressors not being as efficient as a rotary. Problem I ran into last year with my 1st generation ISX Cummins is they run everything up front off one single serpentine belt, and Cummins seems to love York compressors, so I couldn't change to a rotary without a major deal I didn't want to get into at the moment.

I would like to resurrect my A model a/c too. I've been studying some hot rod conversions like '32-'34 Ford's with aftermarket air, and they only use a condenser about the size of a transmission cooler. Granted, a truck has more square footage to cool, but why couldn't you have an aftermarket a/c installer/builder make a custom-sized one sized for a truck, and mount it under the floor like a hot rod install? An APU condenser isn't very large either, and you can hang a side of beef in any sleeper when they're running.

Sealing the ductwork is huge too. It's tight getting in behind an A model dash to get that accomplished if it's still in tact, but that's important as is sealing the blower motor housing box as well.

My "Grilldensor" on the A is still in good shape except for the fittings on the side to connect the lines are shot. Hate to put it together to find the grilldensor has a leak so I'm looking at the alternative method I mentioned, of an underneath condenser mounted somewhere else.

One more note: The seal between the radiator and hood is also a little important to manage air flow properly. When I restored my A model last winter, I had the hood off which made this easier, but I took an old 4" nylon strap that was junk off a flatbed winch. I cut it to length vertically and replaced the old, hardened worn out rubber flap seals on both sides with this nylon strap material. It's perfect, in that it's the right width to make a good seal, and flexible to not scuff anything in a negative way.

If the yellow strap bothers you, Rustoleum, Krylon and a few other mfg.'ers make paint in cans that can change that instantly. I can't see it from where I am perched, so I'm OK with the yellow personally.