Can somebody help me? Moisture in A/C?
With this humid weather we have been wanting to use our A/C. The problem is that the system really isn’t getting cold. Cool but not cold. The guy that did our furnance last year reinstalled the condenser unit that we had from a previous installation. The problem is that the unit sat outside for a while disconnected. Apparently this allowed a bunch of water to enter the system which is causing the pressures to spike. The installer is saying the compresser will have all this water in it’s oil which he’ll never be able to remove all of it. He’s recommending we replace the condensing unit. I was hoping there was somebody on the board that would know enough about these systems to help me make a informed decision. Is there any way we can get this moisture out of the unit or is it really toast? Why can’t we just replace the oil? Why can’t just the compresser be replaced and evac the lines/evaporator/condenser?
Certified boat fetish.
Replies
Time to turn to HVAC-Talk. Post your question there, they're tons of AC installers over there.
It's a shame that your condenser was allowed to sit open to atmosphere for a while. Indeed, a lot of todays oils used as lubricants in them are hydroscopic and your only hope may be to flush as much of the system with nitrogen as you can and to follow-up with over-sized filter-driers.
Whether that works out in your favor financially is a whole other question. Installers aren't cheap and so a new condenser may not cost that much more than the maintenance to make the old one limp along.
If you need a new condenser, make sure that a heat gain calculation is performed (i.e. right size the AC system), that the ductwork is right-sized also (i.e. Manual D compliant), and that the lineset linking the condenser and evaporator is swapped. Ideally, you'd also swap out the evaporator as anything that contaminated the condenser probably contaminated that as well.
First, I would recommend that you find a competent service person. The one that told that they could never get all of the water out of the system does not, in my opinion, fit that description. Request or demand that they be NATE certified.
A few things need to be done to make this system work the way it is designed to work.
First is that refrigerant (freon, R22) in the system needs to be removed with a recovery system. A recovery system will remove and store the existing freon/oil charge and has a filter/drier that removes entrained moisture and contaminants from the refrigerant. The system will need to be purged with nitrogen. Compressed nitrogen is extremely dry and will remove most traces of the water. A liquid line filter/drier should then be added to the discharge of the condenser coil, upstream of the service valve. If the condensing unit has an accumulator/oil separator upstream of the compressor, a suction line filter drier is not really necessary. Without an accumulator, I would add a suction line filter/drier as well. Then a very good (28-29" Hg) vacuum should pulled on the system. Recharge and adjust to acheive the proper superheat (or subcooling with a TXV) at the conditions at the time. Run it untill the house is at the desired temperature and then perform a final check/adjustment to the charge.
Unless your AC unit is 10 years old or older, replacement is not warranted. The service required will cost you several hundred $$, at least, but a new AC could easily run a couple $$K. If you do decide, after having a reputable service company estimate what the service will cost you, that a new unit is in order, I would still not go back to "the guy that did our furnance last year".
Ah!I had to check the profiles. There are two different Timbo's, not one Timbo wiht split personality.I was confused when I saw the first post from "you".
You probably want to get your terminology right. The evaporator coil is the one that goes inside the furnace, and the condensing coil goes outside with the compressor.
Whatever bozo left either unit unsealed is at fault here. The system should have been properly evacuated, the freon recycled, and the tubing ends sealed, whether things were going to be stored inside or outside.
It's certainly worth a try having the system re-evacuated, the dryer replaced, and fresh freon put in. The oil in question sits in the compressor, and replacing it implies replacing the entire outdoor unit, which is to say essentially the entire AC.
Good advice with one additional comment.
Check if your compressor is a reciprocating or scroll compressor (a scroll will be higher than it is wide by a factor of 2 or so). If a scroll, they use a synthetic polyol ester oil that does not like to release water molecules even at 200 micron vacuums. (I can't recall the chemical ring details of why so hygoscopic or retentive of H2O, read it once but getting old). A mineral oil compressor can be dried with a 500 micron vacuum fairly easily, with the synthetic you will have to heat all the lines and compressor to 70-80C to get the water out even under vacuum according to what I've read.
Would not hurt to even put 2 dryers on the line when you try the fixes like Dan and Timbo (II) said, they are only about $15 each.
Dan, Timbo (II) - query on same subject but a little different - have a 7.5 ton old evap (old Carrier brand copper lines) that is open with no leaks, but have no idea of its history. Have a 4T scroll on the shelf to do a DIY GSHP using the Carrier part as indoor coil (condensor in HP application). Query is how to clean it - plan on flushing with ferric chloride solution to get rid of oxides, then water flush, followed by 200 micron vacuum overnight or until it will hold/show better than 500 micron vacuum for a day. Ever tried this, any other ideas???
JH,
There are some commercial cleaners available, their intended use is for changing a system from R22 to R410a, when line set replacement is not feasible, but, I don't carry them in my shop and don't recall the details of the product. Your coil is copper tubes, with aluminum fins (right?) so the ferric chloride should remove minor copper oxides. Maybe some chemists out there have a better idea. I am no chemist (just an engineer). Pressure test the coil after you have flushed all of the cleaners out with N2 if you have the capability. I have never tried what you are going to do, so you may want to check so more sources (ask the oldest guy at the local Johnstone Suppy).
Dan,
I made no mention of the evaporator coil in my post and I am quite clear on the terminology and the technology. You, it seems, may not be.
The fact is, it is a common practice to pump down a condensing uint before disconnecting it for what ever reason. This done by running the system for at least 15 minutes and the closing the liquid line service valve. Allow the compressor to pump all (or most) the refrigerant into the condenser coil and then close the suction service valve. Unless the service valves are shot, no further closure is necessary except maybe to tape over the cut tubes to prevent the intrusion of debris. The unit can then be stored inside or outside.
IF a system were left completely open, then the PROPER evacuation of the system WILL remove all oil and moisture or leave so liitle behind to be insignificant. This is assuming that the system is an R22 system and that the vacuum is in the 500 micron or better range. If I work restoring such a system to service, I would purge with nitrogen to assure there remained no debris, blockages or moisture.
Should the compresser need replacement due to improper storage and subsequent damage, that is an easy enough repair and by no means would require "replacing the entire outdoor unit, which is to say essentially the entire AC". A replacement compressor is still a fraction of the cost of an entire condensing unit, and a small fraction of a new system.