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jdunmyer
06-06-2010, 08:19 PM
My shop A/C is from a walk-in cooler, it's a Frigidaire belt-drive compressor on the condensing unit and one of those semi-circular evaporators. The paddle fan on the latter has been replaced with a small furnace blower w/filters.

The system uses R-12 refrigerant. I charged the thing upon installation in 1980 or so and have topped it off maybe once since then. I started it up after the Winter rest a few weeks ago and noticed the sight glass was full of foam/bubbles. A couple of days later, it started short-cycling, which I laid to low suction pressure due to low charge. Had the remains of a can of R-12, so I weighed it and hooked up the guages. I'm pretty sure the can is now empty, the weight declined by 1# 2 Oz. It now weighs 6# and I can't feel any liquid sloshing around.

The sight glass went "clear" almost immediately when I began charging, but now, a week or so later, seems to be full of bubbles again, albeit not nearly as bad as before.

Question: should I put in more refrigerant? How much more? There's a receiver under the base of the compressor that looks to hold a couple of gallons, so there's little danger of over-charging.

Or should I just junk the whole outfit and get something more modern?

JoeFin
06-06-2010, 08:39 PM
Might have the chunk the R-12 and go with 134a but more importantly is how you going to find the leak.

Black_Moons
06-06-2010, 08:51 PM
Yea at this point I don't think the problem is charging it but finding the leak. Iv read here many people recommending dye designed to be put into refrigerant systems, its fluroeses under UV light so its easy to find where the leak comes from, and does not make a 'visable' mess.

Warning: I have 0 experiance with AC units, but I did stay in an air conditioned holliday inn.

HSS
06-06-2010, 08:57 PM
Look for any oily spots on the unit, the line set and the evaporator. A lot of the time, the leak will be on the outlet of the expansion valve. It is the largest flare nut on the metering device inside the cooling coil. it should be on the left side back kinda to the left and behind where the fan motor used to be. Check it with soap bubbles with the unit off, that way you will have more pressure at that nut.

Patrick

jdunmyer
06-06-2010, 09:41 PM
Look for any oily spots on the unit, the line set and the evaporator. A lot of the time, the leak will be on the outlet of the expansion valve. It is the largest flare nut on the metering device inside the cooling coil. it should be on the left side back kinda to the left and behind where the fan motor used to be. Check it with soap bubbles with the unit off, that way you will have more pressure at that nut


Patrick,
The compressor does have an oil film on much of it, but I blamed that on loosing a bit of oil/refrigerant when connecting the charging hoses. I used to have an electronic leak detector, but traded it off shortly after getting this thing running. "It's going now, with no leaks, I'll never need it again!" I do have one of those old propane-torch type of leak detectors someplace, but I don't know how good they work.

I was kinda figuring that the shaft seal might have a bit of leakage, does that sound like a possibility? Heck, we used to charge our automotive A/C systems every Spring! I think I have another can of R-12, sure wish I'd have bought several back when I had the chance. Woulda been a better investment than most of my stocks. :-(

Bill736
06-06-2010, 09:51 PM
If you can't find and mechanically repair the leak , perhaps one of the combination dye/leakstop additives will work. I believe some of those products did not actually contain Freon R-12, so they may still be readily available. On the subject of AC, how can I determine if the AC system on my 1989 Chevy pickup contains R-12, as filled at the factory, or has been converted by a previous owner to R134a ? There are no fitting adapters in place, but they could have easily been removed after charging. The compressor is cycling every few seconds, and needs charging, but with what ?

Don Young
06-06-2010, 10:01 PM
I would doubt that the R-134 adapters were removed. A set comes with each conversion kit. They are supposed to remain in place and a sticker is supposed to be attached indicating the conversion. Even if it still contains R-12, you may be better off to convert to R-134. It is inexpensive and I have had good results with all of mine.

HSS
06-06-2010, 10:52 PM
jd, if the shaft seal is leaking there isn't much you can do about it cause I don't think there are any seals still available for frigidaire open compressors. I would still check the outlet of the TXV as they will work loose with the constant warming and cooling of the nut. It will cause it to back off it isn't locked in place with some thread locking compound. I use some stuff called Leak Lock for the threads and flare on the outlet of the valve.

Patrick

Edit: If you can find the propane torch (Halide Torch) and it still has the copper in it, it will work just fine for a leak the size you're describing.

rdfeil
06-07-2010, 01:48 AM
JD,

HSS has the right idea. The propane halide detectors are actually more sensitive than most of the electronic ones. One thing to remember about those detectors is that they create phosgene gas during the reaction to freon, so use with good ventilation and try not to breath any of the reactant gas, nasty stuff :( . Oil is a very good indicator of a leak. Look for it around all connections and valves. The shaft seal may well be the source of the leak. If it is don't necessarily write it off as junk. Many seals are available for very old compressors or many generic viton or buna n seals will work just fine. After you find the leak you will need to pump the system down before you solder it or open the connections. I don't want to try to explain exactly how to do this in generic terms here, so do a little looking on the internet for help. After the repair you will need to hook up the vacuum pump to get rid of the air and then add refrigerant as needed. On a system like you have described you can just add refrigerant until the bubbles in the sight glass go away and you should be fine. Check the glass from time to time and add a little if you see bubbles. The charge is not critical like an automotive system is because you have a receiver for the excess. I hope this helps.

Robin

dr pepper
06-07-2010, 03:59 AM
I dont know about the us, but in the uk r12 is now outmoded and unavailable, so is its replacement r22.
I just had an inspection on our chiller plant for our process, and the machine used r22, and at great expense I had to have the unit drained and re-charged, I think the new stuff is A099.

HSS
06-07-2010, 10:56 PM
dr pepper
R-22 is still available here but it is not a replacement for R-12. You said you had an inspection of your chiller. What kind of inspection? Was the chiller low on refrigerant? If not, why remove it?
We went thru the same crap here with R-12 and R-502. I guess the gov't has gone thru all the tax money they collected on those refrigerants.

jd, don't worry about the phosgene, you ain't got that big a leak.;)