streetsnake

So I’m hoping the get the auxiliary fan and condenser hooked back up tomorrow. What should be the first plan of attack? Use a drill to turn the compressor to distribute the oil around the system? After words, once I get the high side and low side hooked up to the vacuum, how long should I run the pump? Do I have to be worried about sucking any oil up? Am I shooting for a specific number? Once I hit the spot, do I pull the hoses off and see if vacuum remains constant over night? Thank for leading me down the correct path.

Eplebnista

It doesn't matter when you spin the compressor as long as you do it before have the engine spin it at 700 RPM.

Running the pump for an hour if you are getting a good hard vacuum should be enough. You want at least 27 inches of Vac and 30 is optimum.

Close all your valves and see if it holds overnight.

If you haven't changed your schrader valves yet, do it now. These are often forgotten.

streetsnake

Close all the manifold valves? Then open them up in the morning check the number?

I don’t think my instruction diagram is labeled correctly. Lol. Couldn’t make sense out of the charge line and vac line. You can see they contradict each other. (Pic vs. diagram). Anyway, ran vacuum for 3+ hours. Seems like it is holding. Fingers crossed. Will check later tonight and in the morning.

Eplebnista

Wow, lots of valves and lines on that set. I have two valves and three lines on all of my sets. This apparently gives you the option of having a vacuum in the charging line which is nice feature. You can either pull the vacuum and let it be or close the valves and then crack them when you want to check the vacuum after letting the car sit.

mj1pate

Second on that. Your new compressor will have new Schrader valves of course, but your suction line Schader valve should be replaced if not already.

streetsnake

I took the shark down to the AC guy today to get charged. The good news is when he hooked his gauges up, apparently it still was holding vacuum. The bad…I received a call saying he was not able to get the clutch to engage, thus only getting 2 cans of r12 put in. He said if he had the wiring diagrams he would be willing to trouble shoot some but I thought I should do my due diligence. I started with the guide that was recommended earlier in my post above. Very nice resource btw. I started by testing the two wires that hook up to the freeze switch. Only one of them was getting 12 volts. I went back to the HVAC controller and pulled the wires coming off the relay. The red one was getting power but the purplish one was not. I’m not sure if I’m troubleshooting shooting this properly so your input would be appreciated.
EDIT: after I thought about for a bit and reread the directions, I saw my error. I reconnected the wires to the relay and reconnected the wires to the freeze switch then retested at the terminals of the freeze switch with wires connected. 12v on both. Moving onto the Freon switch.
2nd Edit: diagnosed the issue. Freon pressure switch. Clutch is engaging, all is good. For amount of R12, it is 1050g for a ‘79 correct? I don’t have rear AC, even if that was an option?? The AC guy was saying 860 but I was thinking that may be for when using r134? Can someone please confirm that?

Petza914

Most.likely the low pressure switch preventing the compressor from engaging. That's near the front of the car. He should try jumping that now that he has 2 cans in it and see.if the clutch engages. If not, he should try the same with the freeze switch.

streetsnake

As always, right on the money. Low pressure switch. It’s ready to be finalized. Yay!

FredR

The first step in the ac charging process is to get the system pressurised to the same pressure as that in the charge bottle and that varies with the temperature and type of refrigerant inside the bottle. This static pressure will typically be in the region of 40 psig to 50 psig. The low pressure switch is set to make contact at about 25 psig as I recall. The amount of charge varies depending on whether R12 or R134 is used and whether there is a rear ac unit fitted but in round terms the 928 ac system fill capacity when fully charged is about 1kg. To get the system up to the pressure of the bottle takes about 200gms of refrigerant and to get the low pressure switch healthy takes about 100gms of gas.

Once the low pressure switch is healthy the engine can be started and the compressor should then kick in. When this happens the suction pressure drops as the discharge pressure builds and then more gas can flow from the bottle into the system. When underfilled the system will typically show lower than normal suction and discharge pressures and when correctly filled the suction pressure with the engine spinning at 2k rpms and the blower working mid to top range should be about 30 psig and the discharge pressure about 210 psig- efficiency of operation and ambient temperatures will affect those numbers but such is what I typically see when the ambient temperature is about 30C.

If the low pressure switch is not healthy the system will not function and when healthy both terminals should show12 volts just as with the freeze switch. Given you report 12 volts at the freeze switch you know the HVAC relay is working OK. If the low pressure switch is healthy you should find 12 volts on the ac solenoid feed cable in the 14 pin connector of the front of engine harness. I cannot remember the terminal number but it is the terminal that has a black cable leading to the engine.