Factory A/C question, '72 GMC

[Ozark Tim]

Didnt get time to post pics today. Will try again tomorrow.
Wish you were a little closer I would say take a ride over and check it out in person.

[Ozark Tim]

Here you go Harry.
You can see the yellow arrow is pointing to the 1 1/4" hole I made in the evap coil box. If you are uncertain you might want to start out smaller and use a scope and light to see before you make a larger hole.
The red arrow is pointing at the hose coming from the engine with hot water supply. When the a/c is on the valve shound have a vaccum signal and be closed preventing the hot antifreeze to go into the heater core. Where the red arrow is pointing will eventually get warm from conduction but it shouldnt be so hot you cant touch it.
OK, I am still trying to get the picture of the hole I drilled in the heater core box bottom inside the cab to download off my phone. I think it loaded up here, lets see.

[harrydunn]

This is excellent, Tim. Definitely some stuff for me to check into. Thanks for posting. By the time I get it fixed, the snow may be flying!

[mrein3]

Originally Posted by harrydunn

A few questions.

1) Loosened the compressor sump plug and there was pressure inside. Normal? I tighened it back up without checking so I could post on here first without opening it all the way up.

2) Compressor is engaging so added a can of R-12 I had laying around. A/C line running into the firewall box was ice cold as I would expect but I never got any cooler air out of the cab vents.

I'm all ears!

I didn't notice this mentioned earlier so I'll say it now. Well I guess Ozark Tim is mentioning it but let me word it in a slightly different way. Is the heat shut off? If you still have a vacuum controlled heater control valve, is it working? A good way to check is to get the vehicle up to operating temperature and carefully feel both hoses to/from the heater core. If they're both hot, your AC may be cooling but your heater is still heating.
If "A/C line running into the firewall box was ice cold as I would expect" is true, your AC is working, you just need to figure out how to get that cold air in the cab. It could be the heater is on and/or 40 years of mouse druff is blocking efficient exchange of air in the system.

FWIW, my system is a cobbled together stock system. I didn't bother to get a heater control valve thinking I would wait until I knew it was all working. I simply plumbed a ball valve into one of the heater hoses. Valve is closed now. I'll open it this fall for winter. If you aren't sure if the shut off is working or not, you could put in a temporary manual valve and shut it off. I would do that before I started drilling holes.

[harrydunn]

Good stuff here. Will definitely check it out.

Tim--

The evap boxes on these are a split design. Would you not be able to undo the bolts holding each half together and crack it open?

[harrydunn]

Good stuff here. Will definitely check it out.

Tim--

The evap boxes on these are a split design. Can you unscrew the bolts holding each half together and crack it open?