Air Conditioning - A/C Unit Chills Out While Were Sleeping

I just dont get it. The last couple of nights one of my window units has been freezing up on me. It doesnt do it in the daytime, no matter the temp setting, or duty cycle.

The room it is in must be temp controlled. It is very small, less than 100 ft sq., and we use a kiln in there which generates alot of heat. The unit is a 5000 BTU window type of unknown make and model. I estimate its age at 10-20 yrs. It was the only 110 unit I had, so until I get another 30 amp line in, I'm stuck with it. Dont want to buy a new unit when I have a 12,000 BTU sitting in the shed. I have had intermitant icing problems with this one in the past. I just cant figure out what varibles are causing it.

Most ppl I have called, say it needs freon. Seems reasonable, I dont have a problem having it serviced, but I'm not completely convinced thats the problem.

We fire at night because

1. It's cooler!
2. When you wake up its done!
3. We can work in the daytime without the kiln running (the radiant heat is like standing in front of a stove)

On a hot day 90+, I can set the stat on 5 (halfway) and it will keep the room at a steady 71 all day (kiln off). No freezing up, and the duty cycle is very low, I would guess its off more than its on. I can also turn the stat all the way up on that same hot day. The compressor will run, and run, and run, and it will get very cold in there, but the evap coil wont freeze. At night when the kiln is running, it feels like it might run 60-70 percent duty cycle (I'm guessing of course).

Anyway, the stat usually stays on 5, keeps a regular 71 degrees. Yes, the unit is always on except for one hour in the early morning (everything needs a rest).

Well, the last few mornings I woke to find the evap coil half iced. I quickly deiced it with isopropanol, and some time later all was returned to normal.

Whats happening here? Any comments welcome.

<insertnamehere>

/edit
If I do need freon:

1. How much (typically) does a pound cost?
2. Estimate the total capacity of a old 5000 BTU
3. What is a reasonable labor charge (I would take unit to them)

Answers to those questions would help me not get gouged!

Thanks :)
/edit

It is dirty or it needs refrigerant.

You can replace it for far less than you can have it repaired for. I've seen them at the home center stores for $100.

if the temperature drops at night and the sun goes off the condenser it will effect the suction pressure.so with the same setting it actually cools the room quicker with a lower suction temperature causing ice...might try a higher setting at night 6 or 7 to see if it still cools the room without the ice.

If you are not already running the fan on the A/C at the highest speed you might try that in addition to Sminker's suggestion.

The unit is clean, so no issue there. Last night it did NOT ice up and I have not changed the setting.

Still puzzled. Thanks for all the replies.

@daddyjohn

They are not less than $100 here. A cheap 5k BTU will run you $199-$250 new.

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a/c fan speed in on high. Thanks for the help :)

/edit

username...man..where do you live..those prices are HIGH!

I live in the southeast US. Thats why I asked the questions about the capacity of a 5k BTU unit, how much a pound is usually charged, and whats a reasonable service rate to pay if I bring the unit to them.

Any idea. I'm still not convinced it needs freon, but I would like to be able to plan for the cost if I need to.

Thanks :)

/edit

I forgot here is a typical price here:

Frigidaire at Lowe's: 5,000 BTU Mini Window Room Air Conditioner (http://www.lowes.com/lowes/lkn?action=productDetail&productId=68868-2251-FAX050S7A&lpage=none)

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/edit2

almost forgot, then add %10 sales tax :P

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Funny..it must have recognized me and gone to my local store...for me it shows $99.98 +tax. And I'm in a hot area as well.

It lists for $208. With %10 tax that puts it at about $230. I noticed you were in AZ, maybe the demand lowers the price there.

Thats why I asked what the capacity of a 5k unit is, whats a typical cost per pound, and whats a reasonable service charge, if I take the unit to them.

Any ideas? I've never had one filled.

/edit

still not convinced it needs freon. No one has been able to explain that either

/edit

Ahh...I see..for whatever reason, the model in the link you provided shows $99.98..but the next step up..also a 5000 btu IS $208...they look almost identical except for a feature or 2.

Who knows...

Have you actually called the store..or just searched online?

I would think way less than a pound for that size, but with labor and misc charges you'd be over $100. And its a sealed system, so IF it is low, then you have a leak. Good money after bad if it doesn't help.

Have you checked the output air temp when its running well? That plus inlet air temp should tell you if its low or not.

Unfortunately I think the common opinion on small units like that is if they last 5yrs, you consider yourself lucky.

I have not called or looked online. I would rather not buy a new 110 unit when I have a great 12k BTU in the shed, and I'm only paying my friend $45 to pull the new 30 amp line. He works two jobs, and does side work, so getting him here can be difficult sometimes. He is certified electrician, so I only need call the inspector afterwards. He has promised in the next 4 weeks, his word is good, but I need a quick fix.

I dont mind paying a little to fix the unit. I was hoping I could get this one charged for around $50, but I cant even get a fix on a price. I always try to do some research before I talk to service personel for an estimate. There are some shady people around. Anyway, no one around here seems to know, so I guess I will have to look around.

Anyway, I am reluctant to ditch it because it cools so well, and I almost never have problems out of it. Last year it froze up maybe 5 or 6 times (it was in a bedroom then no kiln). Hard to remember cause it will do it for a day or two, then not for maybe 5 or 6 weeks. Then boom, out of nowhere it will freeze up overnight for a day or two. And last year it was in a small bedroom, so there was no kiln either.

The output air varies by what you measure it with, but the consensus of several digital temps is 62-64 deg. as long as the compressor is on regardless of outdoor temp.

Its old, its ugly, it looks like the devil cursed it LOL. But it works GREAT. But once in a blue moon it freezes up, always overnight. No explanation.

If it leaked coolant then why would it be intermitant?

It's highly unlikely you could get a certified technician to even look at it for fifty dollars.

Prior to the USEPA rules requiring certification for anyone handling refrigerants and/or the parts of a "sealed refrigeration system" (some twenty years ago) it would have been fairly easy to DIY this or have a local handyman fuss with it. That is no longer the case. Now the ONLY refrigerant that can be purchased without having the EPA certificate is R134a which to my knowledge is only used in automobile air conditioning systems.

It used to be fairly easy for someone with a little bit of knowledge to purchase a "tap valve" and install it on a sealed window A/C or a home refrigerator and add a bit of refrigerant but those days are long gone and will never return.

About the only thing you can do is suffer along with your present unit until you get the new electrical for the unit in storage, or you can purchase a new unit that you can use today.

Sorry.

Am I to understand your saying a window unit does not have the capacity from the factory to have the coolant serviced?

I must be misunderstanding you. That makes no sense.

Still no one can say on thing about why it would be such a rare occurance.

Well, yes, window units are made to not be serviceable. They do not have service valves. It is part and parcel of our "throw-away" society. It is no different than a Sonicare toothbrush that cannot have the battery replaced after it no longer accepts recharging.

But someone DID say why your icing may be a rare occurrence. Sminker posited that it could have something to do with changing ambient conditions in both the room and the great outdoors. Refrigeration is a dynamic thing and it CAN and DOES change depending on several variables.

I know this doesn't help you and for that I'm sorry.

honestly, I could barely understand what he was talking about, the sun, and the condenser and some suction.

The temperature always drops at night, so I dont see a relationship there. If I set it on 7 it will get to about 68 even with the kiln running. I might try 6, that sets it at about a steady 70, and 5 gets me almost 72, which is where we like it.

Thanks :)

Found the answer:

6. Outdoor temperature too low.
Icing can occur if the outside temperature falls below 60 Degrees Fahrenheit. If the outside temperature is too low the air conditioner pressure-temperatures can be affected. When the outside temperature falls the cooling coil temperature will also fall. So much that the coil will refrigerate the room air. This will result in the cooling coil beginning to produce ice. This problem is more prevalent in the fall. If it is hot during the day but cold at night suspect this problem as the cause of icing up. If this problem is suspected try running the air conditioner in the fan only position. Leave the re-circulating vent open. This will circulate the room air without cooling it, while bringing in a small amount of outside air during the night.

number 7 would also apply (oversized air conditioner) since the unit is rated for twice the sq ft.

Dont know what I'm gonna do. Thanks for all the replies and the interest :)

source:

Why Window Air Conditioners Ice Up (http://ezinearticles.com/?Why-Window-Air-Conditioners-Ice-Up&id=214617)

sorry for the tech rambleBeer 4U2Beer 4U2Beer 4U2........the best thing for your unit is direct sunlight on a hot day any change with the night and a cooler temp and the demand inside stays the same...you will ice up