Hi all,

Hoping for some input from those who may be a bit more familiar with some nuances of automotive AC systems. The AC on my truck has been inoperative for years, and this week, I set out to get it up and running again for the summer. I've found my leak and ordered a new part that should, barring any other smaller leaks that weren't apparent before, solve the problem. The compressor and electronics function correctly, so my instinct is that once I fix the leaks and charge it up, I should have working AC.

If the AC had just recently suffered a leak and been addressed relatively quickly, here is my understanding of the steps to fix it:

1. Fix leak and ensure that the system can hold a vacuum
2. Replace the receiver/dryer
3. Pull a vacuum on the system for about an hour to pull all moisture out of the system
4. Refill with the correct quantity of R-134a

Do I need to do anything else because the truck has had ambient air in the AC system for so long (again - years)? From what I understand, most of the oil just sits in the compressor, so it's presumably still in there, but I'm sure that being exposed to air for so long didn't do it any favors. Do I need to add a measured amount of oil to the system, should I just use R-134A cans that have oil included, or should I just add straight R-134A? Is there anything else I'm missing in my list above?

I've found the following information about the normal levels for filling:
R-134a: ~24oz
Dens Oil 8: 6oz

Thanks so much for the help!

 

Talk to any local repair shop or garage. They should have an A/C cart that does all of the steps automatically -- vacuum, recovery, leak testing, and volume and oil charging. The one at the end of my street charges about $100 for the whole process.
You might want to ask them if they can just pull a vacuum on the system first, to make sure you've taken care of all the leaks.

 

If you have those tools than yes your bang on
fix leak
pull vaccum even better if you have a micron gauge if so pull to 500 microns if not 1 hour should be plenty
no oil is needed just weigh in the r134 a or if you don’t have a scale go by the 134 pressure chart. About 15-25 psi low side and at around 100 psi discharge. With system running

 

Great - thanks for the responses, guys. I have a vacuum pump and manifold gauge set already.

I think the purpose of pulling a vacuum for a long period of time is to ensure that all of the water vapor in the system boils off and is removed - I don't have a micron gauge but I think most people just read by PSI. I was planning on using a combination of weight and pressure considerations - obviously if I buy two 12-oz cans of R-134A and I can empty the can as much as possible, I should be in good shape, but I'd use pressure readings and vent temps to confirm I'm in my target.

My only concern was any extra steps specifically with regard to the oil levels that might be recommended given how long the system was broken. Sounds like there's nothing to worry about there. Thanks again!

 

I did exactly that about two years ago. I had pulled a vacuum after replacing the drier and drew it down to -27PSI for about an hour and let it sit. The needle never moved, and then in about 45 minutes it returned to 0 over about 30 seconds, which bummed me out. I repeated it a couple more times and each time the same thing happened. The fact that it never moved, until it did move, was strange to me but I figured I had nothing to lose other than $20 worth of R134a. I added a small amount of PAG46, don't recall how much but it wasn't a lot and fired it up. I jumped out the high low switch on the drier to get the compressor to turn on and charged the system with R143a. I don't have my gauges handy but I think i was closer to 30low and 150hi, but don't quote me on that. AC worked great until the frame rusted through and I had to take truck of the road. It was still holding pressure when I took the compressor off a couple months ago.

FFW to this year, since that compressor and condenser were known good I moved them into the new truck and drew a vacuum. It held for about 30 minutes so I called it good and waited for a warm day to swap in a new drier and fill it with refrigerant. Foolishly I connected the AC compressor's electrical connection and a couple of weeks ago it warmed up enough that having the heat on 72° caused the cabin to heat up such that the HVAC engaged the compressor. Suddenly I heard an awful squealing, kind of a groaning/squealing from under the hood and I knew what had happened. I pulled over, shut it down and disconnected the compressor, which eliminated the noise when I restarted, however I'm unsure of how much damage may have been done and am wondering if it's even worth try to fill it or if I should put the untested compressor back in.

 

Just trying to follow ... the compressor kicked on with no charge because the pressure switch was still jumped from previous troubleshooting, so the compressor ran with no refrigerant or oil?

 

That's a great point! The switch was not jumped, and most likely that was my logic regarding hooking up the compressor connector because I would not have wanted to risk having it come on with no charge/oil. The system was definitely discharged, I had installed the compressor just days before and intentionally did not install the drier because I wasn't sure if the rest of the system would hold vacuum and didn't want to waste it.

I can't explain why it came on but the compressor was definitely engaged and not just freewheeling.

 

Got it - empty system, compressor kicked on. There must be a fault with your pressure switch. Not sure what you're looking at for long-term compressor damage, but I wouldn't be surprised if the squeal persists or comes back.

Mine has been plugged in and empty of refrigerant for years, and the compressor doesn't run so I'd imagine that you have some kind of electrical fault. I already confirmed compressor and pressure switch functionality.

 

Well, I guess if it's a crap shoot either way I may as well install the original compressor and charge the system to see what happens.

 

Can't hurt to grab a multimeter and test the pressure switch while you're there - if there's a leak in the future, a faulty switch will just cook your compressor later. The switch is closed when pressure is good, and open when pressure is bad (either too high or too low). Unfortunately the diagnostics on the HVAC control panel aren't really helpful for diagnosing issues with the AC itself so you'd need to do it manually.