Dockside Chat - Home HVAC....another one, 1/2 frozen coil

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PP1
03-29-2012, 06:56 AM
My central air conditioning coil has frozen up ˝ way a couple of times now. The first time it did it a couple of weeks ago I replaced the filter……it was time, but not in bad shape. It’s run fine for a couple of weeks since and then it did it again last night. We have only needed it at night so far (I need the room just a tad cooler than it was outside). Seems odd to me that it only freezes ˝ the coil.


http://im1.shutterfly.com/media/47a2dd08b3127cceffefcbadca4300000030O00AaN3LRs5Zt2 gPbz4E/cC/f%3D0/ps%3D50/r%3D0/rx%3D550/ry%3D400/


Long back story, short the install on this thing was terrible. I think they put it in sometime around 1999 and we bought the house in 2004. A couple of years ago we opened up the wall so we could get access and see / clean the coil. It was essentially plugged up with stuff. We have since cleaned it the best we could (2 or 3 times). The plan was to replace it this year or next, but my wife was unexpectedly laid off just before Christmas so we are really hoping to push that out a little farther.

I am assuming the likely culprit is low Freon since the air flow seems to be ok (except when it is ˝ ice), but admittedly I know very little about these things.


davedowneast
03-29-2012, 07:22 AM
The short answer is, call someone to check it out. It's that time of the year that you should have the annual service done anyway.

I'm curious, what does the setup look like when the AF is in place? Is there a grill or door? or just the AF? Also, try leaving the fan in the ON position at the thermostat till you get it resolved. Make sure all the ice is gone before starting the AC (the fan on will help with the thaw).

PP1
03-29-2012, 07:50 AM
The plan is to call someone, but thought I would post the question here too, I’ve gotten a lot of helpful advice from here both from my threads and searching others.

This unit originally served the whole house, upstairs and downstairs. The previous owners put a large addition on to the far end (upstairs and downstairs) and never did anything with the AC. Last year we put a new system in for the upstairs portion (mini split with heads to serve the individual rooms). To keep the air flow to this unit we had them add a large duct to an area that was always very hot. It’s a big hallway and stairs open area and never did have a vent in it.

The original install for this AC sucked air through the wall cavity as it’s return. There was a 20 x 20 grill at the bottom of the wall, this coil was ˝ way up the wall, and there were holes in the walls of the rooms upstairs that were meant as returns from the top floor. With the studs in the walls it essentially had to pull through the top and bottom wall cavity (3.5” depth x width between studs. The filter was a pain to get to. The coil was essentially a solid mat when we opened it up to start the cleaning process.

Last year I built box around the coil in the wall cavity and used the AC mastic (sure that is the wrong term) and put that filter frame in. The filter is 24 x 24 and is resting on the grill / door in that picture.


aln
03-29-2012, 08:20 AM
We always had problems when the AC was left on overnight. If the econmizer was pulling cooler outside air, instead of warm inside air across the condenser, it would freeze up by morning.

davedowneast
03-29-2012, 08:24 AM
It sounds like you're doing your best to make a piss poor installation as good as it can be. The immediate problem may be freon or if the air flow is minimal for the AC size (certain conditions will freeze the coil). What's the AC tonnage? It could be that while solving the upstairs problem and the warm spot problem, you may have inadvertently created a new problem. A 24 X 24 grill is good for about 4 Tons. A 20 X 20 pleated air filter is good for (2 1/2 Tons)?, I don't have the AF info in front of me. I think the filters are rated for CFM's on the packaging when you buy them (400 cfm= 1 ton or 12,000 BTU's).

The long range answer is, tell your wife to get back to work so you can afford to redesign and replace this system. :grin:

debugger
03-29-2012, 08:25 AM
Low freon will cause them to freeze up.

Rustybee
03-29-2012, 08:52 AM
Low freon will cause them to freeze up.




X2 :thumbsup:

PP1
03-29-2012, 09:14 AM
It sounds like you're doing your best to make a piss poor installation as good as it can be…..

Yes, the improvements we have made have brought it up to a poor installation….a vast improvement (not being sarcastic with that statement).


…..What's the AC tonnage? It could be that while solving the upstairs problem and the warm spot problem, you may have inadvertently created a new problem. A 24 X 24 grill is good for about 4 Tons. A 20 X 20 pleated air filter is good for (2 1/2 Tons)?, I don't have the AF info in front of me. I think the filters are rated for CFM's on the packaging when you buy them (400 cfm= 1 ton or 12,000 BTU's).

I believe 3 tons. Basically I got the biggest filter I could get if I didn’t plan far enough ahead and had to go to one of the big box stores to get a filter. The installer for the mini split system assured me it was more than adequate size wise. We use 24 x 24 pleated filters.

We did this in Spring 2011 and worked all last summer, at least as well as could be expected. The whole house with this thing and the new mini splits upstairs.


The long range answer is, tell your wife to get back to work so you can afford to redesign and replace this system. :grin:

I know, I keep telling her that but I think she (and the kids) are really enjoying her being off. If we had more warning of this layoff (time to prepare) I would enjoy it a lot more too.

Low freon will cause them to freeze up.

It was the ˝ frozen thing that got me. Did that both times while seeming to work fine for a couple of weeks in between.

baypro21
03-29-2012, 09:17 AM
Yep, it's low on refrigerant. Low air flow would have made the whole evap coil ice. When it's running only 1/2 your coil is full. Take Dave's advice and have it thawed out (by running fan only) when the tech gets there. You don't want to pay for extra time for him to thaw it.

Also, you have a leak somewhere. AC's don't use refrigerant, they are supposed to just circulate it.

baypro21
03-29-2012, 09:26 AM
We were posting at the same time. It seemed to work fine after thawed because you are not needing the full capacity of the system yet. With only 1/2 the coil being able to absorb heat your 3 ton system is now around 1.5 tons, enough for March. Try that in August and see if it seems fine.:grin:

Most leaks are in the evaporator coil. That could run $800 to $1800 depending on coil cost and access.

If you decide to just refill it you need to keep an eye on how it's running. It's not good for the compressor to run it when the system is low on refrigerant. That's a very heavy duty 230VAC motor and pump in a sealed housing that relies on freon flowing thru it to keep it happy.

davedowneast
03-29-2012, 09:35 AM
baypro brings up a very good point about leaks. When the service tech adds refrigerant, it's a band-aid. I used to tell my customers that if it needed freon more than once a year, I'd have to do what may be a costly search for the leak. If it would last more than a year, we would just charge at the beginning of the season (I sold R-22 for $6 a lb at the time).

Now, things are a lot different. You probably will have to give serious consideration to replacement. Hopefully, the band-aid will last long enough till you're in a position to make the necessary changes. Be prepared for all new equipment, probably a different size (tons) and duct changes and/or additions.

davedowneast
03-29-2012, 09:38 AM
"We were posting at the same time"

ditto :grin:

PP1
03-29-2012, 12:25 PM
Thanks for the input fellas :thumbsup:. You've pretty much confirmed all of my suspicions. I really hope another band aid will help stretch out the project until we are ready to do our major remodel where we do plan to change everthing around.

:tht_rulez:

baypro21
03-29-2012, 12:30 PM
You're welcome. I hate to tell you but R22 has doubled since last year. I'm at $60 per lb.

natecert
04-07-2012, 04:40 AM
Baypro and Davedowneast are correct. It sounds like your putting off replacement. I would suggest during the service call to have the tec. at least do a visual for a leak or an electronic leak search if they do not charge too much. You just may get lucky and have a failed braze joint or rusted out line dryer. If no obvious leak is found I've had some luck with Easy Seal. It will seal SMALL leaks.
Rule of thumb for filter grill size is width X height X 2. Nominal CFM is 400 per ton.

By the way, if an electronic leak test is to be done, have the system off for at least four hours B4 the service call this will make the leak search more accurate, the refrigerant will pool in the leak area. Do not let the tec turn the system on until you have decided on the leak test option.

Best of luck! Yea I'm in the trade.

billinstuart
04-07-2012, 07:48 AM
I agree with low refrigerant. I've got 2 systems with tiny leaks we can't find. A few years ago I bought 3 bottles of R22 on the black market and I add a lb. or so when the pressure drops..every year or 2.

Bought 3 bottles for $200. Hell, I've MADE money..................

tinmarine
04-07-2012, 09:56 AM
Curious on how the coil was cleaned, who did it and with what. You said it looked like a mat when you accessed it. You can clean the surface, but it can still be plugged. Possibly.



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