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My unit ices. up. Tech checked the Freon and said it was…

Customer Question
My unit ices. up...

My unit ices. up. Tech checked the Freon and said it was right according to specs. The condenser coils were cleaned. The air filter was changed. The evaporator he said was clean. The evap. fan was cleaned and the fan motor was replaced. The thermostat was changed. Still the unit ices up the suction line. What could be the problem?

Contractor's Assistant: Did you double-check the thermostat's settings? And what about the filters?

The thermostat was set at 75. The filter was replaced with a new one. The same kind being used for years.

Contractor's Assistant: Do you plan on doing the work yourself?

At this point I don't know what to check next and evidently the tech I called didn't either. I can do everything except the Freon because I don't have a license any more. I retired.

Contractor's Assistant: Anything else we should know to help you best?

The tech said the evap. coil was clean but I didn't see it. Is there any thing else that would cause this problem or should I pull the evap. and check it myself?

Submitted: 10 months ago.Category: HVAC
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Answered in 36 minutes by:
7/17/2017
HVAC Technician: Phil, Mechanical Engineer replied 10 months ago
Phil
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 9,391
Experience: Retired HVAC/ Electrical & Boiler contractor. Industrial
Verified

Hello, about the only thing that will cause the coil to ice the suction line is not enough warm air flow across the cooling coil....return air should be in the 72 to 75F range, not cooler.

if there is a bypass duct installed between the supply and return and it is open.. that will cause the return air temprerature to drop below 60F and that will ice the coil and the suction line.

.

Sometimes the duct liner used in some configurations comes loose and blocks the air flow in the system.

.

If it is a new system, and the evaporator is more than 20% smaller than the condensing unit, the coil will run colder and sometimes frost the suction line.

.

Tell me what the head and suction pressure reads were and the exact indoor and outdoor temperatures at the time, with that information I can assess the situation more closely for you.

.

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..

.

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..

.

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.. ...

.

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..

.

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

.

.

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Customer reply replied 10 months ago
I will check for a bypass and blockage but don't remember seeing either. The Tech that checked the evaporator coil said it was clean but I am not so sure now. I will check it myself. The tech didn't tell me the pressures so I will have to check them myself tomorrow. Thanks
HVAC Technician: Phil, Mechanical Engineer replied 10 months ago

Thanks, ***** ***** see you tomorrow

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