A/c not building pressure

[Custom 68]

Wow glad you found it. I'll be curious how much frean it actually takes

[tinman_local2]

Post back once you get it going. This one has peaked my interest. It's nice to find a weird problem, and finally get it resolved. I fought a leak on a Saturn recently. All new parts, I mean ALL new. Kept losing a charge after a few days. Finally added dye to the system only to find a leaky o-ring on the compressor. New part; wasn't tightened up from the factory.

[Davidf]

Replaced hose and now working.

Held vacuum for 30 minutes, so charged to 275psi/45psi at 90 degrees at idle. A bit higher pressures at revs. Seems like it could be colder, but decent. Need to insulate lines just outside of evaporator box. Cycling switch working and condenser fans operate with compressor. Will test in heat of day tomorrow.

[Custom 68]

Awesome deal!

[Davidf]

Update: Not as cold as it should be. Will need to fine tune refrigerant charge...probably overfilled at this point as the suction line at compressor and the compressor are sweating. I think this means refrigerant is not completely turning to gas inside the evaporator (i.e. liquid refrigerant making it all the way past the accumulator.

Anyone want to offer advice on getting the refrigerant charge perfect? Cannot go by weight as this is not a factory configured system any longer. I probably have about 36 oz in the system.

[kwmech]

did you replace the condenser?

[Davidf]

No. But, taking that into account, still not cold as it should be. Condenser has two 12" electric pusher fans in front of it to help shed the latent heat.

Follow-up: Drove the truck in 99 degree heat this afternoon. The a/c kept me comfortable, but not frozen out. I think the condenser fans are doing an admirable job because the temp stayed relatively the same (according to the calibrated back side of my hand) whether moving or at a standstill. So, I have decided to installed a manual heater water shut off valve. I believe the factory vacuum valves are normally open and close with vacuum. So, when you shut off the engine the valves open (assuming stored vacuum leaks, which I am sure it does on these old vacuum switches). Anyway, when you restart a hot engine, you are undoubtedly getting hot water circulation into the heater core for a short time. Now, the a/c has to cool the heated heater core and thus cold air is slow to return. Anyway, that is my theory. My vacuum valve works because if I start a cold engine and let it warm up, the heater circuit is relatively cool past the vacuum valve. Shut the engine off and restart after a few minutes and you can feel the temperature difference at the heater hoses.

[jjzepplin]

I always do as said above- just sneak up on the correct charge. This means to add a little at a time until you are freezing out of the cab or car. My last car had 40 degrees at the vent in the driveway. Almost 20 when moving down the road. This was in Florida summer. I am about to do a LS but plan on using a Sanden SD7 but with 1999 Trans Am components and stock ECM running it. Should be fun. So I am "in" for a happy conclusion.

[Palf70Step]

With the factory AC, there should be a vacuum controlled valve that shuts flow of water thru the heater core when AC is running. Mine was missing and I put in a manual cutoff valve on the heater hose inlet and that helped the feel of my AC a lot.

[Bigdav160]

charged to 275psi/45psi at 90 degrees at idle

That's too high - both low and high pressure. I bet the vent temp is above 50 degrees

Low side needs to be 32-35

[Davidf]

Originally Posted by Bigdav160

That's too high - both low and high pressure. I bet the vent temp is above 50 degrees

Low side needs to be 32-35

You're about right on the vent temp. Going to reduce charge this weekend.