Can I just pull a vaccum for a while to avoid replacing an AC dryer?

I'm about to replace the expansion valve on my WRX that has had the AC out of commission for about a year. They system was evacuated, so ideally there's no moisture in it. That said, they always say to replace the dryer when the system is apart.

The dryer on the WRX is part of the condensor, and is therefore both a PITA and expensive to replace. If I held the AC system under a vaccum for say 24 hours would that dry out any moisture that the dessecant had gotten a hold of, and avoid replacing it?

Expansion valve + gauges + vacuum pump + R134 = ~$150.
Condensor / Dryer unit = $300

I've never replaced the drier. Just suck the system out and you'll be fine.

I just did the same thing on my 2005 Saabaru ...well actually dvot on this board did it...anyhoo, he replaced a perished o-ring, vacuumed, added refrigerant and POW! cold as a well digger's ass again :) A month later and it's still running strong.

Also, "rent" a vacuum pump from Autozone - they have the professional grade ones. They may also have an R134 gauge set you can "rent"

fifty wrote: Also, "rent" a vacuum pump from Autozone - they have the professional grade ones. They may also have an R134 gauge set you can "rent"

Whoa. Great idea. Didn't know that AC tools were in their program. Awesome! Thanks for the heads up!

The longer you vacuum, the more water will boil out of the dessicant. The only time I've ever had a failure caused by the drier was one that had been open for a loooong time, and the dessicant bag burst. That plugged up the expansion valve in a heartbeat.

My Nissan truck had a problem with the dessicant breaking down and leaving the dryer and clogging the expansion valve. At least that what they said and they showed me the stuff they cleaned out of the system.

For what its going to cost you to replace the condenser, try what you are asking first.

My wrx's (2002) dryer was next to the radiator- about $15, just make sure the O-rings are the right size. Took me twice to realize the ones that shipped with the new drier were incorrectly size. HF has the gauge sets for $50 and a vacuum pump for around the same price.

Teh E36 M3 wrote: My wrx's (2002) dryer was next to the radiator- about $15, just make sure the O-rings are the right size. Took me twice to realize the ones that shipped with the new drier were incorrectly size. HF has the gauge sets for $50 and a vacuum pump for around the same price.

Yeah - some WRX's got a cheap stand alone dryer, and some got the integrated one. Mine is the integrated one. :(

My wife says come by, you can pull a vacuum all you want. She can't help with the AC whatchamgiggy though

Wally wrote: My wife says come by, you can pull a vacuum all you want. She can't help with the AC whatchamgiggy though

Something something I'll show your wife what to pull something something...

If you can, try to source a "real" vacuum pump, not the venturi / air powered ones. You need to get down to 28 inches or so for awhile (over night should be fine).

Kendall

I used a Harbor Freight venturi vacuum 'pump' on my Miata and it still blows fairly cold. I don't think I replaced the dryer.

Good to know Autozone rents real vacuum pumps if I ever need one again.

In reply to DILYSI Dave:

I'm a mobile A/C Design Engineer. Most of what's been said is correct. You have to get down to 29.2" HG before you can boil the moisture out. The dessicant in modern driers doesn't absorb a significant amount of moisture unless there is some kind of flow through it, so just exposing it doesn't ruin it. However, you will get moisture in the system, so a complete evacuation is necessary. If you use a vac pump that will pull down far enough, the longer you pull that vacuum the better. Ideally, you want whatever you are using to charge the system hooked up along with the pump so that you aren't connecting or disconnecting any hoses between evacuation and charging. You can do this with a properly valved manifold gauge set or a charging station. If you can't do that, at least make sure you purge the charge hoses before hooking them up. This is a common mistake people make and it introduces moisture and air into the system, killing it's performance.

OK - making progress! I bought and installed the expansion valve. PITA, but nothing too magical about it. Hooked up the gauges and found a leak simply by the residual pressure that was in the gauges (yes, someone returned gauges to Autozone with 100 psi in the line). O-Ring on the compressor outlet that got crushed when the last AC guy wrenched on it I assume. Fortunately, the O-Ring was the same size as the ones on the original expansion valve, so I replaced it, and the leak went away. I have pulled a vacuum for the last half hour and it is now sitting to see if I have any leaks.

One thing I am unclear on is whether I want to add oil. Some sites say to add oil any time the system is opened. Some say only when replacing components. Now I did replace the expansion valve, but the amount of oil lost there was inconsequential. So - on a system that has the original compressor, condenser, dryer, lines, etc., that is undergoing a vacuum, do I need to add oil? Will it hurt if I overfill it by adding some now without it needing any?

Also- when adding R134 - The WRX takes 15 - 19 ounces. I got (2) 12 ounce cans. How do I tell when to stop adding from the second can? And I assume I do that by closing the low side valve?

EDIT - Dammit. There's a leak somewhere. Vacuum fell from 30" to 10" in about 20 minutes. Grrr. Tips for finding leaks?

EDIT #2 - Hmmm - Leak might have been my fault. I pulled the vacuum then shut the compressor off without ever closing the valves. So it could be leaking back in through the pump. Attempt #2...

If theres no evidence of oil leakage at the leak site, don't bother adding oil.

Is there a small kitchen scale in your house?

Don't overfill it.

I'm watching this thread, as I'm gonna have to do this at some point to my 97 Impreza too..

Good to know about autozone offer the pump and manifold.

One thing I want to add, 30mins isn't really long enough to pull the vacuum from what I've been told. Ideally, I've been told to let it sit overnight but if that isn't possible, 2-3 hours should be good enough.

get a bottle of N2 it's dry pump that in add a small amount of 134A then use a sniffer to find the leak. fix the leak pull vacuum, fill with N2 let it sit 20 minutes or so pull vacuum refill with N2 this time run compressor for 1 minute let sit again, pull vacuum and refill with 134A

The N2 will pull out ant moisture and dry out the dryer.

44dwarf

Good news - Edit #2 fixed it. Pulled the vacuum for a half hour, then shut the valves, then turned off the pump. 5 hours later it's holding steady at 30". I'm going to let it sit over night, then get back to it in the morning. Should be 14 -16 hours by the time I get to it.

There's no reason for there to have been oil loss. The system stayed closed. It was a bad expansion valve that killed me, not a leak. As long as pulling the vacuum doesn't cause the oil to vaporize and get pumped out, then my gut feeling is that the oil is fine.

YAY! I HAVE AC AGAIN!!!!

Thanks for the help guys. Until now, I could say "I do all my own work except for AC and painting". Cross AC off the list. :)