AC troubles. Anybody with experience?

[steamin10]

WELL it looks like I am going to swelter for a while. My Carrier 3 ton unit shut down. It started running on and I got a whopper of a power bill last month. The condenser had to be cleaned of that annoying fluff from cottonwood, but the A coil began freezing over. Hooking up my gauge set showed a low charge, so I dumped some r-22 into the system. Because my scale lost its mind for lack of a 9 volt battery, I dont know how much I put in, deciding to go by the seat of my pants.

This is a Carrier 3-ton unit that was installed a few years back, bought as a take out unit. It has been running well, except it has a minor leak, last year took a coupla pounds of gas. Now after charging, I have low suction pressure. While I was charging by the gauge I was getting 45 lb lowside, (or 15 degree baseline temp), and running up to 190 highside. It looks like I have a failing A coil due to blocked capillary tubes., as I cant seem to get a good lowside number to come up. Static charge number is about 110 lbs with 85 ambient, and the unit is always in the shade.

Anybody got an opinion? The unit is now shut down as it froze out again.

[Dave_C]

Ok,

I've been working on and designing these things for 40+ years, let's see what we can do.

1. If you had ice on the indoor coil, you won't get the suction temp up till it is completely thawed out! The ice blocks the airflow and that makes the coil evap pressure run low. (low airflow means low heat exchange)

2. Cotton wood trees are death to A/C units. You have to wash the coils from the inside out to get the stuff out. It gets pulled in by the condensor fan and is hard to get back out. That does not cause freezing but it will cause high head pressure and a high utility bill.

3. If you tell me the SEER of the unit, I'll tell you what the head pressure should run given the OAT.

4. Not likely you have a clogged cap tube. It is a closed system and there is nothing to clog it unless you've had a compressor burn out and no one cleaned the system. I've never encountered a clogged cap tube in all the years I ran service calls. Frozen or stiff oil may clog one temporarily but it will soften as soon as you thaw out the evap coil.

Certain Carrier systems were known for small leaks. The ones with the flare nut connections were the bad one because the summer heat followed by the winter cold (contraction/expansion) caused them to loosen over time.

The best way to thaw the indoor coil is to put the fan switch in the "ON" position for two hours. Don't run the A/C during this period!

Let me know if you need anything else. I'll do what I can remotely.

Dave C.

[steamin10]

OK, the unit is a 3 ton Carrier, 10 SEER r-22. I ballooned out the plenum over the upflow furnace, and removed a 2 ton that did not cool the house. It had a 4 part A coil, that froze 3 parts, due to cap blockage. Waving a torch over the cap tube would cure the problem only to return some days/weeks later.

In consulting with a former co-worker still active in the business, he advised I probably have a 'dirty coil'. This is what frosts me, as I have many animals and all the hair and dander that follows. I religiously change 16 x 24 air filters with the Mantards cheepies, and they always have a coat of fluff on them. At any rate, it seems plausible that the a coil may have insufficient flow with escaped material blanketing the fins. I will see today, but it will be difficult as the over-sized coil is shoe horned into a small space. The cabinet is not designed to service things in such a way to provide handy access.

Yes it has those annoying unions. They are pretty much out of the picture, as it is all soldered. I am embarrassed to admit, that in one of several attempts to eliminate pin hole leaks, I had to change out an elbo, right at that connection, as I blew a hole through it trying to get it hot enough. It still seeps in that area, to my displeasure.

I have the schooling and training to do all this, but I am panicky due to the expenses involved, and se I am not thinking clearly. Too many irons in the home fires. Thanks for the reply.

[Dave_C]

Big Dave,

I can relate! I get a little paniced when it is my unit as well!

Sounds like you may be short on air flow but if the unit charges out right and is clean is will give you a good TD across the evap coil.

Fixing pin hole is fun isn't it! NOT

Dave C.

[Dave_C]

Big Dave,

You mentioned some cap tube blockage that was solved with heat. In my experience that is a pretty good indication of moisture in the system. It freezes then thaws on off cycles or with heat. As you know, it is not all that hard to get moisture into a system. Gage hoses not kept closed off and the ends closed is just one.

I had to replace my indoor coil at 15 years of age. Started to leak on the lower rows where the condensate sits in the pan. Copper coils, steel tube sheets and water equal rust over time. I'm told the newer 100% aluminum coils don't have that issue. The old Carrier aluminum coils got pin holes like crazy but Carrier finally got smart and started using some better aluminum!

I'm still running an R-22 system as well (Rheem) but I know I'll have to go to 410A when I replace it. I'm not a fan of the high head pressure 410A but there aren't many options. R22 is getting hard to find at any price! (Even with a Universal EPA card in my wallet)

Dave C.

[spro]

na

[steamin10]

A promised I tore into the furnace plenum, and took out the top case panel of the furnace to access the a-coil. What a mess. The entire inner surface was covered with a cheese cloth of tightly knit floss of hair and dust, that (luckily) pulled off in big sheets. With Mom proping up the coil at an angle I got in and got my hands to pull the layers out, and used a finger nail/knuckle brush from the sink to rub up and down the fins to knock off the rest, and a lot of corrosion of the fins. I kicked the unit on, and got air flow, but no cool. The system is flat overnight. It doesnt rain, but what it pours.

So the rest of the afternoon was about puzzling how to get (afford) a replacement, and a call to a friend turned up a matching coil, and off we went. It turned into a 3 hour tour, on motionless I-80, but Rose is good company when not road raging at shoulder speeders, and other cheats. The Unit is nearly exact fit, except with standard lines instead of a dopey nutted fitting. It is good shape without the corrosion of mine, but stored outdoors. So I will close it up and pump it down for moisture removal, and see if it holds a vacuum. If good I will proceed to make the change and pump the system down before gassing it up. So here is hoping I can find all the fittings and taps in the box I work from. (Cost me $30).

Lets see now, in the basement pile, or the garage pile....It is all organized.

R-22 is plentiful here, there are guys that sell reclaimed gas for about half, but I wont buy it. There are flim flammers that will top off a bottle with LP. $250 a 30lb jug is common, across the counter a bit more, and multi sales of virgin sealed bottles, less. I buy part bottles by the pound, so with the black valves there is little risk, if you get later bottles. 410 is everywhere and about $260 a jug if I remember my last inquiry, so running R-22 is not that big a bite. I found a wholesale salvage guy in Lebanon IN, that has some 60k ft of NOS AC and handler equipment, much of it ding, dent and dry R-22 stuff. Its a ride being just out of Indianapolis. 22 is not going away, as there are many bottles of virgin coming out of storage. My last bottle dated to '04, and came from half a pallet being sold off. I just cant abid the pace of the work.

Ok, so thats the plan, I'll post when done. Thanks for the thoughts to sooth my panic. After all, what could be worse than having it be junk?

[steamin10]

Monday got to be a classic hectic day, starting with Expressway traffic going to the supply house to get my required brazing rod, and supplies to change out the A coil. I bought a big tube of 15% brazing rod, white flux (not needed really) and some tubing turns, and sleeves and reducers.

Mom interfered and called upon one of her friends who is in the business, and he came by before I got done fiddling, and took over the lead on the project. I had the system pumped down, and the compressor unit seemed tight, but the coil side would not hold. He was down on Nitrogen and could only get about 60lbs on the system, so I unshipped my Argon for my welding, and he blew 200lbs into my system, and we immediately found blown out cap tubes and connections hidden on the coil. He pointed to oil stains, that confirm a long term leak. So zip, and the tube cutter made short work of the lines, and the used coil was then positioned and brazed in place. There was some fun, as the tubes pulled apart from tensions on the lines hanging in space, so it was some acrobatics and holding the lines steady while brazing with a coat hanger for a hook to pull the errant lines into control, for the confined area. Putting a 100 psi test on the assembly proved it is good to test, as the high side line was open at the joint, somehow incomplete. We hit it again, closed it off, and pressured again. A simple soap solution spayed around all the joints, in and out, revealed a service tap on the suction side making profuse fine foam. So that is the project for today to get the sealer in the tube to seal both caps on the service valves.

We finished by blowing off the pressure and pumping down to a hard vacuum, turned my 22 bottle upside down to suck liquid into the system, fired it off and waited for the pressures to stabilize while running. I closed up the plenum box that has a couple of leaky areas, that will be silver taped over later. He warned me that tape is my friend, and using sheet metal screws around the A coil in tight fits, can lead to punctures, so be sparing. It should be noted, that in a previous replacement, I put a pregnant bump out onto the plenum to accommodate a larger a coil than original, and this leaks a bit along the sides. this allows the 17 x 19 standard coil to sit above the furnace heat exchanger without problems.

So just in time for a cool nights sleep, He got some chicks for his yard, (they were going to buy them anyway), He used all my supplies save for one missing coupling for the liquid line I did not have (oops, that would have cost the day there) so it did not hammer on his truck supplies. So the final real cost to me, was $30 for the used coil, (should have been $300 new) about $10 a pound for 13 lbs of gas, part loss due to the blowout. (his company charges $80 a lb by weight) I lost a few lbs of argon, but that is expendable for use anyway, and in this case was crucial to the testing. about $120 for the 28 sticks of silver braze, of which we used two sticks, the rest into my inventory, and the few taps and other such that fall into my (somehow lost box of parts) inventory. Carlos got $60 for his pocket, and will probably get likewise in the near future. So while not free, the catastrophic and intimidating failure, was not too bad, and like most problems, Murphy raises his head, so you have to keep yours and solve each step of the puzzle. I dont like to fail, nor have my decisions over ruled, but in the end I am short on experience, and welcomed the helping hand. It did shorten the trail, as I was moving slow so as to eliminate mistakes ($) on my part.

So in the aftermath of a good nights sleep, I get to be thankful for some volunteered help, wipe off my tools and torches and organize things they way they should be, after being adrift for a time. So the collateral organizing is all good to. I hope reading this diversion, may serve some purpose at solving similar challenges, when things dont go quite right. Dealing with internal angers, visions of failure, and the discomfort to follow through and get it done, is why fixxit guys get payed to go where others fear to travel. A big thanks to John and Carlos for being there and being my legs when needed. Thanks for reading this little adventure, maybe it will hep someones spirit to know not everyday is a romp in playland.

[steamin10]

I have a leak on the suction service valve, which is where most systems develop a leak on the rubber seals there. A cheat (hack) is to put blue locktite on the threads of the cap, and seal the cap to the valve, slowing the leak rate. So I will have to adjust the charge minorly to get the coil temp above freezing. Thats the easy part.

In serendipity, Son's girlfriends Mom has no AC because of a shutdown last year. So with gauges and equipment in hand, I gave it a quick 1 - 2 - 3 check. I punched the run relay, and it fired up, and it gave that satisfying whir as the compressor started to load. Put the gauges on, and found 100 lb static charge. Thats good, the system is closed and has a chance to run here. Put my bottle on the scale, and sucked some gas in while it ran, and balanced the charge out, by the gauge, using 1.2 lbs. In just a minute or so, you can feel the heat from the condenser coils showing the unit is moving heat. In half an hour the temp in the house was coming down, I collected $100, and everybody is happy, so far. so with only about 4 lbs of 22 left, I have to shop for another 30 lb bottle.

TTFN