any4xx

I used to do my own service on R-12 systems and always went through the vacuum procedure prior to refilling after having a system open. The 134 system on my Chev. truck is kaput and I need to replace the pump and accumulator. The parts guy told me that you don't need to vacuum the 134 systems prior to charging. My gut feeling is that he's full of poopie, but I've never worked on a 134 system.

Anyone out there can set me straight???

Thanks, Tom

65Z01

Yes he is...the laws of physics don't change depending upon the type of refrigarent!

Air doesn't go through a phase change like the refrigarent does so you need to get it out of the system before charging with refrigarent and lubricant.

96Silver_Conv

He's full of it but you also have to change the drier DONT leave the old one in, try to get it down to 30 or as close to that as you can come. The longer the better 30 minutes is good. Easy way is to get 1lb cans read compressor data plate see whats full (4.29lbs etc.) and go from there so you don't overfill. Have fun :cheers:

jefft84

molecular structure of the chemical does not change the procedure of proper service, suck it down before you add.

SunCr

Pag oil, which was in it from the factory, has an affinity for water. If you don't vacuum the air out (boiling the moisture out that's in it), you will be seeing your parts guy many times over. However, are you sure it's the compressor? Many of the Chevy truck compressors have a press on clutch - they like to work loose. Too loose, and it won't engage or they will slip making all sorts of noise.

oldace84

jefft84,
I'm taking my vette to the shop. Should I have them vav the A/C system before recharge?
Going to use the 12?
thanks
tony

Steve85

And if your talking catastrophic compressor failure, you should also replace the orifice tube/txv, it catches and clogs up with the metal fragments from the compressor.

SunCr

Oldace: Anytime you open up an a/c system to the atmosphere, you will need to vacuum it down. You may not be able to have your system recharged either without fixing the leak. Some shops will tell you it's Federal Law (it isn't), but the California Health & Safety Code is so broad that a shop may feel that they risk a fine or loss of license by knowingly charging leaking system. Current California Law requires voluntary reporting when discharging fluorocarbons or any "greenhouse" gas (so that not only includes R12, but R134 too) - In 2004, it will be mandatory, so it's probably best to get whatever you're going to do, done now.

frank moran

Sun, thanks for the correct info on the r12 capacity, should have been 2 1/4 lbs, when I reduced the 134 charge, cooling improved, thanks again. Charge at 80-85% of the r12 capacity, and as SUN says you need to evacutate...the system
Frank

jefft84

If its been open or even low its best to completley evacuate and leave on vaccum for 30-45 minutes before refilling with freon and oil of any type. I mention the time because alot of techs will short change you and suck it down for about 10 minutes and refill. The labor guides show to bill out 1.4 hours for a reason. Dont let them do a quickie recharge.

any4xx

Thanks for all the replys. I thought that his advice sounded a bit lame. I was planning on the orifice tube, accumulator/dryer being replaced with the compressor.

I guess I'll have to invest in another vacuum pump.

Thanks again, Tom

jefft84

Can I suggest an upgrade to the auto adjust orfice tube for improved low speed and high temp cooling. With no other changes my vent temp went down 15 deg at idle.

95Purple

He is correct, you don’t need to evacuate your system for R134 as you did R12. Don’t know why but you don’t. I have done many systems with R134 and not evacuating it before.

SunCr

Say what? Do you have some formula for adjusting pressures with all those non condensables mixed in? Seriously hope you're not doing conversions by dropping R134 in with something that has R12 in it.

any4xx

Hey Guys. Thanks for the input. I replaced the goodies on my truck this morning then properly EVACUATED then recharged the system.

Tom