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Phil
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 8436
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I coil on my AC keeps freezing up. I don't suspect a plugage

Customer Question

I coil on my AC keeps freezing up. I don't suspect a plugage issue, my filter is only about three days old. Right now I am currently trying to fall the coil just by using the fan "on" setting but the fan will come on. If I turn the thermostat to AC, the fan turns on, but if I just turn the fan on it does not turn on. What am I missing and why is it freezing
Submitted: 10 days ago.
Category: HVAC
Expert:  Phil replied 10 days ago.

Hello, a cooling coil will freeze if the the system is just a few ounces low on refrigerant, OR if there is a lack of sufficient air flow.. OR if the cooling coil and blower wheel are loaded with dirt (seen on older systems, or where a lot of dry wall construction was going on.)

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A cooling coil will also freeze if thermostat is set below 70F on a cool night... AC systems as a rule are not built to run in cool weather. This happens when the house is hot and someone sets the thermostat to 65F or so then goes to bed... it cools off outside, then the cooling coil freezes as the system attempts to cool the house to 65F for example.

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I am a retired mechanical engineer and HVAC/ electrical/ refrigeration and boiler contractor ... with 56 years in this business. The last 20 of those years consulting for major firms nationally..

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All I ask is please select the ***RATING LINK***at the top of your page, that is the only way I am credited through the site. Rating does not affect your charges nor ability to refund if not satisfied..

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If you need to be coached through a full diagnosis/repair, and wiring etc. for up to two days, and wish to be trained to use test instruments...... that goes well beyond' Just a simple Answer' of course.. ...

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rate my simple answer so far positively..and I will deliver that training and coaching to you All on the same dime so to speak.

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If you can agree to that, rate now, lets continue by all means.

Customer: replied 10 days ago.
OK, so it's not freezing up because of temperature outside, The system is clean, both the coil and the wheel. The furnace is about eight years old. Was installed when my house was built. It's a temp star two-stage furnace. Central air
The airflow for the last eight years has never seem to be an issue. Like I say this is the first time I've ever had any problems with it and I checked all the known suspects, I just barely got the coil on phone and restarted the system. I'm wondering if it's refrigerant. Is there anything that else that you would have me check? Also why will my fan not run when I turn the fan to position on but AC off.
Customer: replied 10 days ago.
Coil unthawed not "on phone"
Expert:  Phil replied 10 days ago.

Thanks, ***** ***** are nearly 100% that the system has a very tiny, very slow leak, and is 3 or 4 ounces low on refrigerant.... those sorts of leaks are almost undetectable, so we use a chemical leak stop that can be injected into the system.

Expert:  Phil replied 10 days ago.

A decent HVAC repair outfit willl charge you $300 for the leak stop fluid installed, and $20 for a few ounces of refrigerant. Others might be two or three times that. It will pay to shop around.

Expert:  Phil replied 10 days ago.

An exception would be a system that does not use a 'piston/orifice' metering device but instead use an expansion valve and the power head on the expansion valve is going bad (5% chance) of that.

When you have all that you need please select the 'finish and rate your expert' link near the top of your page to close the question, I will appreciate it.

Your positive rating is the only way the company pays me for my work, lacking that I work at a loss. Thanks!

Expert:  Phil replied 10 days ago.

Regarding the fan not running in Fan ON mode, the thermostats fan switch could be bad (20% chance)...

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or the installer needed to use that wire, to power the C terminal on the thermostat ... because there were only 4 thermostat wires pulled, and the thermostat needed 5 wires....

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so that 'Fan ON' function was sacrificed.

Expert:  Phil replied 10 days ago.

Make very sure that the fan runs in cooling mode.

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Use a thermometer poked deep into one of the cold air vents to measure the temperature... if its colder than 55F when the house is at 72F inside then there is insufficient air flow through the coil... or the system is a few ounces low on refrigerant.

Customer: replied 10 days ago.
The fan does run when the AC is in cooling mode. And the fan on function has worked in the past including up to last week with the AC in non-cooling mode
Expert:  Phil replied 10 days ago.

Thanks, ***** ***** the fan switch in the thermostat has failed, you can test that my removing the thermostat and fitting a jumper between the R and G terminals on the thermostat, If the fan runs, then its a bad fan switch in the thermostat.

IF the fan does not run then there is a problem in the printed circuit board that will require its replacement.

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Customer: replied 10 days ago.
OK I will try the jumper. If it does come on is that switch a repairable item or regardless the thermostat needs replacing?
Customer: replied 10 days ago.
Also I don't have just an R
I have a red wire coming into a RH?
Customer: replied 10 days ago.
I have G O B Y1. W1
Expert:  Phil replied 10 days ago.

The fan switch on the thermostat is not repairable... however it might just have oxidized contacts that you can fix by working the switch about 20 times with the power off to the furnace.

Jumping Rh to G will work

Customer: replied 10 days ago.
That might be one of the problems. Also I have a zone system for my upstairs, can you tell me how I can jumper out the dampers so that I don't know if it's going open and or closed?
Customer: replied 10 days ago.
I did not have much airflow upstairs, and if it's not going all the way open that could be one of the reasons I am thinking in my mind anyway for airflow restriction and coil freeze up. When that zone tells it to get air can't move enough air to do any good and is freezing up
Expert:  Phil replied 10 days ago.

That would get us into over time and its getting later here.

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If you would like extensive training and coaching on the repair just rate this answer so far positively and I will spend up to 2 days coaching you starting tomorrow AM

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Without a rating I loose my shirt on these questions that go into over time

Just rate my work so far and I will hold the question open for you

Customer: replied 10 days ago.
I see how you might could see it that way, I see it is still an airflow issue and that is the reason for my freezing up. Whatever you want to do I guess , If you think my situation is solved which it's not then I guess we can be finished if you want to help me diagnose the airflow as for my coil freeze up we can carry-on.
Expert:  Phil replied 10 days ago.

That would get us into over time and its getting later here.

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If you would like extensive training and coaching on the repair just rate this answer so far positively and I will spend up to 2 days coaching you starting tomorrow AM

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Without a rating I loose my shirt on these questions that go beyond just simple answer

Just rate my work so far and I will hold the question open for you

Expert:  Phil replied 10 days ago.

Your situation is not solved, but I cannot guarantee to fix complex issues on line for an unlimited time without some sort of compensation.

Diagnosing air flow requires some test instruments, that work is generally not done by home owners. However as I posted earlier if you can poke a thermometer deep into one of the cold air supply registers and tell me what it reads I can pretty much tell from that, if the air flow is sufficient or not.

Customer: replied 10 days ago.
Thanks for your help phil I'll just find somebody local that can help me further
Expert:  Phil replied 10 days ago.

Your situation is not solved, but I cannot guarantee to fix complex issues on line for an unlimited time without some sort of compensation.

Diagnosing air flow requires some test instruments, that work is generally not done by home owners. However as I posted earlier if you can poke a thermometer deep into one of the cold air supply registers and tell me what it reads I can pretty much tell from that, if the air flow is sufficient or not.

I would need to know that temperature and room temperature at the time to assess that for you

Expert:  Phil replied 10 days ago.

Your cost here is only $40... calling in a technician will cost you $125/hr with a 2 hour minimum, and you may or may not get a qualified person.

Customer: replied 10 days ago.
Ok I'm confused. I thought you said that from here it's not something done by the homeowners and it's late where you're at so you were on your way out?