Auto techs/mechs - AC service

[tcsenter]

My father is the consumate DIY'er, even if he hasn't a clue what he's doing sometimes. ;-)

I get home today and he's trying to recharge the AC on my mom's 1998 Dodge Caravan. Luckily its not a conversion deal, but is a factory R134a system. So he's got 3 cans of R134a refridgerant with the low-side fittings, but he has no gauges at all. Worse, he PURGED the damned system completely empty. He said it was 'just air' because no 'milky gas looking stuff' was coming out, it was clear. Maybe that's true, but isn't it 'bad' to do this?

If you empty the system completely, don't you need to pull a vacuum on one end of the system while recharging it to evacuate all the contaminated air out?

Also, what about compressor oil? Should he be adding oil to the system, so much oil for every x ounces of refridgerant added? Is there a separate port/fitting for the oil or can it go through the same low-side service port the refridgerant is added at? Do you add oil first, between cans of refridgerant, or last?

Any advice would be appreciated.

 

[tcsenter]

bump for the night

 

[Bluefront]

Ac service is not for the inexperienced person...you can get hurt.

First why are you doing this? Did it lose the refrigerant? If so, check all the AC lines and other stuff for leaks. You'll see a wet oily area if there is a leak. If you cannot find a leak, the 134a could have escaped slowly out the compressor seal, or maybe inside the car (cooling unit) where you can't see. If it was a slow leak, you probably didn't lose any oil, so its probably not necessary to add any.

134a is clear, so you can't see it. Also, you shouldn't just drain it into the air...not good. If this 134a was drained by holding down the little valve at the fitting, little, if any air got in. So you can get by by just refilling it.

Find out how much 134a your particular car should have. Normally it's 12oz cans you can buy. 2 cans=1.5lbs. Don't add too much.

Using your low-press hose only.....attach the can to the adaptor, puncture the can so you hear the gas start to hiss out, this bleeds the hose of air....then attach the hose to the car's low side. Your low pressure hose won't attach to the high side.

Get a pan of hot water, set the 134a can in the water with the valve completely open, right side up. wait till all the 134a gas goes into the car. You can tell by picking up the can....if it feels cool after a few seconds, there's still some gas left. Repeat the procedure untill the correct quantity is added.

If you think your system lost refrigerant oil, you can buy cans of oil that will install the same way as the refrigerant.....maybe 50cc per can. One can is usually enough.

Be careful....


You can also install 134a by running the car with the AC on....it then sucks in the gas from the cans. However most newer AC systems won't start up unless there's some 134a in the system already. That's why you need to use the hot water trick. Be sure to have the valve open when you do this.... A closed can of 134a can explode if put in hot water.....

I just read Pacfanweb's post. If your father drained out the 134a like you said, there wasn't any way for air or moisture to get in, so drawing a vacuum isn't really necessary....course if you have a vacuum pump laying around, do it.

 

[Pacfanweb]

First of all, yes, you do need to pull a vacuum on it. Evacuating gets all the moisture out, and if the system truly had "just air" in it, and the freon was gone, then it had a leak, and therefore has moisture in the system.
That means that evacuating and recharging is only going to be temporary; the refrigerant will leak out again.

If you KNEW that the system was completely empty, and you KNEW how much refrigerant it was supposed to hold, THEN you could possibly charge it without the gauges, but it wouldn't be 100% accurate.

If you had a set of gauges and knew the system was empty, you could charge the system without knowing how much it was supposed to hold, by watching the pressures on the gauges.