1998 GMC Jimmy AC Recharge

[artbuc]

Buddy asks me to fix his daughter's AC which is blowing hot air. He says AC has gotten weaker every year for the last 4-5 years and now is finally kaput. I can't see any evidence of a refrigerant leak although I didn't bother to look at the evaporator (way too much work). I checked the static pressure. Not enough to move my gage. When I opened the hi and low side there was enough to cause a little puff. I then pulled a vacuum with my 2 stage oil vac pump. System pumped down to full vac. I turned off the pump and waited 15 minutes. System held full vac. Based on everything I have told you, I figured the system did leak very slowly over time. Therefore, I am ASSUMING that the original amount of compressor oil is still in the system and suggested to my friend we recharge with 134a only and do not add oil. I restarted my vac pump and ran it for another 30 minutes and then measured in 30 oz of 134a according to the owners manual.

Did I do the right thing by not adding oil?

If a system holds full vac, does that mean there is a good chance that it will hold at operating pressure? Thanks for your input.

 

[duaneb9729]

In home a/c systems, where most of my repair experience comes from, I have been burned doing what you did, however it was apparent right away when it didn't hold, while adding the refrigerant.

I work on my own cars, and have plenty to learn about car a/c systems myself

 

[artbuc]

Thanks. When the Evap coil went out in my home AC, I lost alot of oil. The HVAC tech installed a new factory coil and did not add any oil! I asked him about it because it was obvious that I had lost alot of oil. He said it was much better to be low on oil than high. And, because he did not know exactly how much oil was lost he strongly recommended against adding oil. That was 4 years ago and the unit is still working great.

When I lost the condenser on my Toyota last year (flying rock), there was oil all over the bottom of the condenser and I added back oil according to the service manual recommendation when replacing a condenser.

We'll see.

 

[duaneb9729]

Our home a/c refrigerant comes with some small amount of oil mixed in it. I suspect your friends car will be just fine.

 

[Chris142]

I always add oil unless the Orifice tube is already dripping with it. Not a lot, 2-4oz which contains dye to help find leaks.

It's better to have a little too much oil than not quite enough.

Too much oil will act as an insulator between the refrigerant and Evaporator.........AC won't blow as cold as it should. But a few ounces wont effect it enough to matter and will increase compressor life.

On your friends Chevy. Look over the compressor closely for a leak. They like to leak on the bottom where you cant see it.

 

[JHZR2]

What IMO you should have done is opened the system. That little puff is not indicative of anything, and the system was essentially ambient pressure. This creates a situation where moisture can get in.

I would have pulled the receiver/dryer, and put some fresh OE oil into it, then done the vac pull, then recharged.

Moisture in the system is asking for issues. Hopefully there is none in there...

 

[artbuc]

Originally Posted By: JHZR2
What IMO you should have done is opened the system. That little puff is not indicative of anything, and the system was essentially ambient pressure. This creates a situation where moisture can get in.

I would have pulled the receiver/dryer, and put some fresh OE oil into it, then done the vac pull, then recharged.

Moisture in the system is asking for issues. Hopefully there is none in there...


Thanks for the response. I may be wrong, but I thought the main purpose of keeping the system at full vacuum for 45 minutes was to make sure all moisture was evaporated and gone. I don't think any moisture can still be there after 45 minutes of full vacuum.

It didn't matter anyway because my friend wasn't willing to pay for anything except the 134a. If it had been my car, I would not have done anything until I knew exactly where the leak was, knew I had fixed the leak, etc, etc.

 

[TedT]

The problem is that if air was in the system the moisture in it can combine with the A/C oil. When you evacuate the system it removes the moisture suspended in the air but not the moisture combined with the oil. I wouldn't loose sleep over it though.
Ted

 

[onion]

Your fix wasn't ideal or 'by the book', but there's a good chance that it'll work ok for a year or so.

 

[mechtech2]

Holding vacuum and holding pressure are not the same.
[Whether in AC systems or cooling systems.]
It's one check, but not final or absolute.
There was no need to evacuate the system.
Adding sauce is what I would have done.

 

[artbuc]

Originally Posted By: mechtech2
Holding vacuum and holding pressure are not the same.
[Whether in AC systems or cooling systems.]
It's one check, but not final or absolute.
There was no need to evacuate the system.
Adding sauce is what I would have done.


"Sauce" = 134a, right? The guy is really hurting for money. Since the system was basically empty, I wanted to pull a vacuum to see if there were a big leak so he wouldn't have to waste money on refrigerant. I told him holding vacuum is no guarantee, but he was willing to take a chance. If the system didn't hold vacuum, he would have returned the 134a and driven with the windows open.

 

[onion]

Oh quit nitpicking, Mechtech. He made a reasonably good shade-tree fix. Not ideal... but good enough. Assuming the leak is small (and it very well might be seeings how it took YEARS to lose all the refrigerant), it'll probably work fine for a year or two.

If not, then he'll have to find the leak. I wouldn't lose any sleep over it.