I'll be getting access to a vacuum pump and gauges next week, so I'm planning on evacuating the system and refilling it. But before I do this, I want to make sure I have all my ducks in a row, so I have a couple of questions.

1. How do I add oil back into the system? Or does the vacuum process NOT remove oil, so I won't need to worry about it?

2. I've heard there are cans of R 134a with UV dye, but I haven't seen any around locally. When I was online, I saw that I can get UV dye in small bottles. Assuming I can't source the R134a w/ UV Dye and have to go with the small bottle, how do I get it added to my A/C system?

Thanks!!

 

What are you doing to the system that it needs to be evacuated and charged? Leak? Compressor failure? Other?

1. Evacuation will only remove a small amount of oil, if any. Parts replacement requires adding some oil back to the system, it can usually be added to the part before installation along with the dye.
The only to know for sure if there is the proper amount of oil in the system is to flush it clean, replace the accumulator and add the factory specified amount.

2. As much as I dislike Auto Zone, they usually have cans of R134a containing dye. They are usually on a bottom shelf near the virgin R134a. They also usually have a UV Dye Kit that has a bottle of UV Dye, a UV penlight and a pair of yellow glasses.

 

My Expedition sat for 2+ years and when I recently went to use to AC, the compressor wouldn't run. I added a couple cans of R134a w/oil that had a cheapo low side gauge and got my AC working again. So far, everything seems fine, but using the cheapo gauge, I'm only seeing a pressure of 25. I'm thinking the leak is really slow or getting the AC running again might have somehow sealed the leak... I don't know but I've got my fingers crossed that the o-rings or whatever that might have leaked have swelled to seal the leak ...

Now today ... I've got access to a vacuum pump and manifold gauges, so I was thinking about checking the pressure, properly, and pulling a vacuum to see if there is a leak. I've since been told that I might be better off to leave well enough alone, since the AC is working. I'm thinking about just checking the pressure and if all is good, to leave it alone. But I'm still thinking about pulling a vacuum and refilling. What had me confused was that every post I saw said to evacuate then refill and I figured that evacuating the system would also drain the oil. I now know I'm wrong. So now, depending on what the gauges end up showing, I have the choice of evacuation and refill or just make sure the pressure ends up being good. What do you think I should do?

Should I just evacuate the system and refill with R134a w/UV dye or should I just make sure the pressure is correct with what I have now?

BTW, based on how much I've already added, the system was just over 1/2 empty. Remember, this was with the cheapo gauge.

 

If the system contains freon, you need to remove the freon first, THEN you can evacuate and refill. As LSRX101, said, you should not lose much if any oil that way. The problem is, I highly doubt you have a recovery system for pulling out the freon. Vacuum pump is for pulling all air and moisture out of an empty system, not to remove freon.

My 2 cents: your best bet is to put the gages on it, run the AC like normal for a test (you can't do it on a cold day or the AC won't run enough), and see if they are in the normal ranges. If so, you are done. If not, odds are you are still a bit low (especially if it is performing poorly) but there is a chance you are overcharged too, but it is not likely. Starting from the condition that it would not run due to apparent low pressure, 2 cans is not likely to overcharge it.

And in the future, skip the cheapo can gage, and put a real gage set on it to begin with. Then you will actually know what is going on before you start working on it.

 

Dave,

I'm confused!!

I thought the vacuuming process remove the freon. My buddy is suppose to be bring a container to store it in. He's in the res/comm HVAC business.

As for not pulling a vacuum on it, do you think it will be fine or would I be better off pulling the freon out, vacuum, then refill?

BTW, you're the 2nd person to tell me to just check the pressure and make sure it was good.

Thanks!

 

Well if your friend is an AC tech, then he will know what to do as all AC systems are essentially the same. You generally need a recovery unit to pull the freon out, perhaps he knows how to use a vac pump to do that. I don't, but I've never had to.

The best way to do it, is to remove all the freon, pump it down as low as possible and refill with a measured quantity of freon to get it right. But before you do that - FIND THE LEAK! It can be hard to do, but if you don't, you will be chasing this problem every year or so often as it leaks down. It could be that it just leaked down due to seals shrinking from sitting, in which case, you may not have a chronic leak. Then all you need to do is get it right this time and it should be good to go.

The easy route is just using the gages to get the system filled approximately right and call it good. It gets you close.

Your friend is an AC tech and will be looking at the car helping you out. Trust him - he knows the technical info and has eyes directly on the problem. Much easier than over a forum...

 

Update... Buddy couldn't make it over to help this weekend, so I picked up the gauges and hook them up.

Outside temp was 79 and when I hooked up the gauges, low side was reading 30 and high side was at 150 when the AC was sent to MAX. I put a thermometer in the center vent and it was reading 75F, after it had been running for about 5 mins.

I added more freon (R-134a w/UV) and the low side pressure was up to 45 and high side went to 160. Center vent temp was 70F. Based on the pressures, I'd figure the AC should be much colder then this, so I raised the RPM to 1500. @ 1500 rpms, the vent temp dropped to 65F. I went out to look at the gauges, foots now off the gas so it's idling, and the low side pressure was back to 30 and high side at 150.

So off I go to add more freon.... I added another 12oz can and low side is stuck at 30 but high side goes to 160. I check the vent temp and it's now down to 62F.

Now I'm puzzled, causing more questions.... Man my heads spinning because I'm not even sure how to ask my questions, but I'll give it a try. I'm now pretty sure that I've got an AC leak, possible a dried or rotted o-ring from sitting so long, but why isn't the pressure dropping lower then 30/150? When filling an AC system, can the pressure drop from running the compressor harder (increased Engine rpms)? If so, shouldn't the pressure increased again once the engine was back at idle? When I added the 2nd can, why did the low side pressure not increase along with the high side? If we were to say there was no leak, is it because it's still just low on freon? Other then a leak, is there something else I should look for? I had read somewhere that high side pressure should be 2.2 to 2.5 times the outside temp. If this correct, buit if not, where should my high side pressure be when the outside temp is 80F?

Thanks for everyones help!!