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O.Topic - T-Bone others....A/C Unit

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Hound

07-21-2005 09:00:32




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Hope someone can help me here, before I have someone else, back out to look at my furnace. The heat exchanger in the furnace is icing up. I've checked the filter, registers and the outside unit. I had some guys in, and they said the freon was alright. I have to doubt they really knew what they were doing though. They wanted to sell me a compressor in the first 2 minutes they were here.

They only odd thing I notice, is the exchanger in the furnace. Its shaped like an "A". One side looks completely frosted ( supply lines and return lines into the little manifold) The other side of the "A" is only frosted up about a 1/3 of the way. A pretty distinct line. What the heck does this mean? I'd like to know a little more about it, before I have someone else in to look at it. Thanks. Hound

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buickanddeere

07-22-2005 06:26:57




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 Re: O.Topic - T-Bone others....A/C Unit in reply to Hound, 07-21-2005 09:00:32  
Is the furnace fan on Auto or continuos? How many ton units and what size/HP is the furnace fan? Has somebody shoved the thermostat as low as it will go ? Some people think the lower the stat the faster the house will cool down. Women are worst. "Saving" power by not running the fan 24/7 And/or running the AC compressor 100% of the time. The evaporator coil never gets a chance to have airflow over them without freon flow to help thaw ice buildup. Anybody shutting the system down at night and opening all the doors and windows?

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Hound

07-22-2005 05:26:32




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 Re: O.Topic - T-Bone others....A/C Unit in reply to Hound, 07-21-2005 09:00:32  
Thanks for all the replies guys. I'm going to try to clean the unit up a little, before I call them guys back.

I was thinking that since it is such a disticnt line were it was frosted, it might have been a "leak" level or freon level or something. Thanks. Hound



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Kevin (FL)

07-21-2005 21:19:45




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 Re: O.Topic - T-Bone others....A/C Unit in reply to Hound, 07-21-2005 09:00:32  
Every time our AC unit freezes up it's been a dirty A-coil (evaporator). (it happens at least once per summer.) I change out the filter every month, sometimes sooner, but every now and then the evaporator gets pretty gunked up with black looking junk. I mix up hot water, dishwasher detergent, a cup of bleach and some laundry detergent in a 2 gallon pump-up sprayer and let her have it--for the bad areas I use a parts cleaning brush. After it's pretty clean I do a hot water (clean water) rinse and also make sure the condensate drain line is clear and the icing problem is fixed.

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RayP(MI)

07-21-2005 18:49:54




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 Re: O.Topic - T-Bone others....A/C Unit in reply to Hound, 07-21-2005 09:00:32  
Had a large 3 room unit freeze up. Found the sensor on the coil wasn't telling the compressor to turn off. Had to replace sensor(S) and control board. Worked fine ever since.



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Kevin Bismark

07-21-2005 18:23:28




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 Re: O.Topic - T-Bone others....A/C Unit in reply to Hound, 07-21-2005 09:00:32  
Yup, these guy's are right, when you have an evaporator coil freezing up the first 2 things to check if it's either low on gas, or not enough airflow through the evaporator, plugged up with lint and fuzz, had one so bad a couple years ago the air compressor almost couldn't blast through the crud



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champspa

07-21-2005 17:22:37




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 Re: O.Topic - T-Bone others....A/C Unit in reply to Hound, 07-21-2005 09:00:32  
your low on freon , the A-coil freezes up partially because of low pressure and there isn't enough freon to frost the entire evaporator.



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gatractorman

07-21-2005 16:21:05




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 Re: O.Topic - T-Bone others....A/C Unit in reply to Hound, 07-21-2005 09:00:32  
Moisture in the system will cause the evaporator/exchanger to freeze up as well. Course the system would have had to been open to the atmosphere for moisture to get in and not enough vacuum pulled on the system to get the air out. Just thought I'd throw that in.



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T_Bone

07-21-2005 13:53:09




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 Re: O.Topic - T-Bone others....A/C Unit in reply to Hound, 07-21-2005 09:00:32  
Hi Hound,

Ahh repair via internet. Hard to do from here but you can get some ideas.

Well don't count the first guys out just yet as they have well seen something on the gauges that made them say it was a bad compressor. I've said the same thing then continued on to eliminate all the other possiblity's of the same symptoms before condeming the compressor.

If they just said it's a bad compressor without checking air flow, coil cleaness on both evaporator and condensor, filters, fan cfm, then you were correct and need a second opinion.

I've even seen a two speed fan where the relay went out hanging the fan motor on slow speed.

I've also seen a under rated unit for the cooling load size freeze up. The cooling system has to take a short break when the evaporator pressures drop very low causing the Evap coil to ice. As the ice builds on the coil, ice becomes a insulator thus less cooling takes place and continues to build until no cooling can happen.

I've also seen closed dampers or a outside air damper stuck open causing the same problem.

Then's there's the really rear problems of the metering valve being plugged or the compressor valves broken or a bad compressor pump.

I've also seen the wrong refrigerant installed.

The guys have already covered the most common basics and I touched on some of the not so common issues but without seeing the unit first hand, it's just a internet SWAG here.

My son just ask me to look at his 3yr old unit. The installer has been back two years in a row to add refrigerant leading my son to think he has a leak in the system when in fact he has a bad compressor pump and the installer has just been adding refrigerant as the pump gets weaker each year trying to get him out of the 5yr warranty time frame. I've only seen this problem about 5 times in 35yrs. I added the correct refrigerant charge and expect the compressor to go out before the end of the cooling season and still being under warranty. T_Bone

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Turtle

07-21-2005 13:44:01




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 Re: O.Topic - T-Bone others....A/C Unit in reply to Hound, 07-21-2005 09:00:32  
I would suspect that the "A" coil is blocked. After you let it thaw out Shine a light through the coils and see how much blockage there is. If the air flow cannot pass over it will freeze up. You can buy coil cleaner from AC shops or you can also use 409 for a temp fix. I have also used Oven cleaner on rare occations when I get one thats real bad but don't recommend this. DIrt will get between the coils and plug them up.

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MeAnthony

07-21-2005 12:03:51




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 Re: O.Topic - T-Bone others....A/C Unit in reply to Hound, 07-21-2005 09:00:32  
My mom's did the same thing, but to a lesser degree. Her furnace is in the basement (old farmhouse, stone walls, quite dirty environment). A filter change didn't help much; turned out the squirrel-cage type blower in the furnace was over half plugged with accumulated dirt/dust. Cleaned the fins and it works like new.



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Bob

07-21-2005 10:42:14




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 Re: O.Topic - T-Bone others....A/C Unit in reply to Hound, 07-21-2005 09:00:32  
Likely, no TXV is used, and there is a separate capillary tube to each 1/2 of the evaporator, (or even a couple of capillary tubes to each 1/2).

Perhaps one capillary tube is restricted.

Other causes could be low refrigerant charge, or something you haven't noticed, yet, blocking the air flow through the part that is freezing up.



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Angle Iron

07-21-2005 10:11:18




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 Re: O.Topic - T-Bone others....A/C Unit in reply to Hound, 07-21-2005 09:00:32  
I am not a AC tech,but have worked this business from a sheetmetal installer up to supervision over the years. That said you cannot determine if the freon charge is right if the proper amount of air is not crossing the coil. This is the case with frost/ice build up on the coil. Dirty coil, dirty filters, poor fan moter or the sofa pushed up against ths return grill. If the so called tech checked the freon charge without clearing the coil his method was wrong. A partialy frozen coil(one side is the other not) leads me to believe low on refrigerant or malfunctioning metering device. Cap tube, expansion valve(some times called a TXV) or the accuator. These are all metering devices.
As I said I am not technician so this is just an opinion. Call another contractor but let the ice and frost clear befor they get there. Angle Iron

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Coloken

07-21-2005 09:53:23




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 Re: O.Topic - T-Bone others....A/C Unit in reply to Hound, 07-21-2005 09:00:32  
If it is iced up, the compressor has to be OK. This "can" happen from too much fluid, but this can no way apply to your unit unless it was over charged recently. There should be enough air flow to keep it from doing this. Most/some units have a thermostat with the sensor bulb right next to the coil so that when the coil gets close to 32 degrees it shuts off the compressor. Get the idea? the unit is cooling faster that the air can move it away. If this were a beer cooler, the answer would be to set it to a WARMER setting. Like others say, improve the airflow. Thaw it out so the ice doesn't block the air and go again. Or set it to a warmer setting.

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R Lee

07-21-2005 09:42:30




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 Re: O.Topic - T-Bone others....A/C Unit in reply to Hound, 07-21-2005 09:00:32  
Is your ducting zoned?--- baffles control flow to different levels--- Heard of someone having these malfunction not letting air flow over the A coil causing the freeze up.



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old

07-21-2005 09:10:01




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 Re: O.Topic - T-Bone others....A/C Unit in reply to Hound, 07-21-2005 09:00:32  
I don't know a lot about them but I know you have one of 2 problems. Either you don't have good enough air flow, I.E. your fan maybe getting weal/going bad. Or your low on freon. Either one of those will cause the problem. I just spent $600 on getting my unit fixed last month. The fan was going bad and cause the thing to ice up and then the unit out side went out also.



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Waltmo

07-21-2005 09:25:15




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 Re: O.Topic - T-Bone others....A/C Unit in reply to old, 07-21-2005 09:10:01  
Old is right. Check air flow. Dirty filter, dirty a/coil, blocked registers or return air any of these will reduce the heat load on the unit causing it to freeze up. These are the usual causes if the freon is ok. Running the unit with it frozen up will lead to compressor failure! It will let liquid freon back to the compressor and in will be damaged. Waltmo



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