pulling vacuum on A/C with partial charge

[lizardflats]

I had to have my A/C evacuated at a shop to remove the evaporator so that I could replace the heater core in our '96 Explorer XLT. The A/C was working fine before the heater repair. I didn't lose any oil in the process and the ports were covered when the evaporator was out (about a week). I've got everything back together now.

I started to do a recharge last night, but realized after putting in about 6-8 oz of R-134a that
1. I need to jumper the low side pressure switch to get the compressor to come on.
2. I really should pull a vacuum to dry out the system.

I can rent a vacuum and manifold guage kit at the local Autozone. My question is whether I can pull a vacuum with the partial charge in the system?

Then, once I have the system pumped down and dried out, I can add the rest of the specified charge (1 lb 14 oz total).

Thanks!

 

[jaeger6]

As a general rule you can't recharge a system without pulling a vacuum. You also find that when you fill a system that is completely evacuated, that jumping the pressure switch isn't really that necessary.

If you were to pull a vacuum on your system with freon in it, you'll pull all the freon out. It should really be removed before you even consider putting a vacuum pump on it.

 

[lizardflats]

I thought so.

Thanks.

 

[ranger7ltr]

And unless you want to have air in the system after evacuation, I would drain whatever oil you still have in the system and replace it... Plugging the system might save the oil from leaking out but moisture will find its way into the oil and the refrigerant oil loves moisture...

And hopefully you are going to replace the accumulator as well...That unit really doesn't like to be reused since the dessicant inside is used to retain moisture in the refrigerant flowing through it...Generally, when you open the system you replace the accumulator and the oil in it and the condensor...

That is if you want an internally dry refrigerant system...

 

[lizardflats]

Well, I got some pretty advice, and I might have to wait a while to afford a complete evac and recharge by a shop.

What would be the symptoms of moisture in the system?

 

[RomeovilleIL]

Moisture in system will have the ac start up and blow cold for a few minutes then just blow hot because ice is blocking the flow of the refrigerant. You'll have good pressure and the system will turn compressor on, just not cold. It's a relative thing though depending on how much moisture is in the air while the system is open. Sometimes you can fill the system and add a can of drying agent and it will operate "ok", sometimes you get nothing. At this point it probably won't hurt to go ahead and fill and run until you can afford to have it evac'd again. You may get lucky and have it blowing cold with a little moisture in it. It's not like the shop will charge you less just because there is only 12 oz in it.