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Furnace freezing up but evap coil clean

3K views 9 replies 7 participants last post by  Ernie in Dawson 
#1 ·
Hey guys

After a few hours of running my furnace it freezes up where the lines enter to the A coil. I just opened it up to clean the coil assuming this was the issue but it looks spotless. Could I be out of refrigerant or could there be a leak? The furnace and house is 17 years old.
These pics I just took of the coil. Is the rusting a sign of anything?


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#4 ·
I'll make it easier. You should be getting cold air coming out that is at least 20 degrees cooler than the intake air. If you don't, that's most likely a low charge issue. You should have good airflow coming out of the registers. If you don't that's a leak, restriction, or blower issue. The compressor should be turning off at some point. If everything else seems good, and the compressor is staying on, it could be the relay.

You could always have a thermostat / control issue...

Off the top of my head, that's the quick stuff to check.
 
#7 ·
Change the air filter, more air flow less ice forming on A-coil.... run the air C. long enough to knock down the humidity level/ dew point temp.

can you program 15 - 30 minute ice melt pauses in the AC programmable t-stat?

Check the drain hose assemblely for free flow, see older AC threads....
 
#8 ·
Also have your HVAC guy check the static air before and after the filter with his digital manometer. And make sure the blower is clean and the motor bearings aren't getting weak. The cooling side requires more airflow so a reduction can cause issues. Dirty filter or blower being one of the most common problems but sometimes those fancy "super filters" that 3M and what-not advertise can really restrict your airflow if you are already a little on the low side.
 
#10 ·
Thought I would just add this to the thread as an example. Was going to a job the other day and the electrician I know from the other side of the building is on his way up to the roof and calls me over. This was the conversation.
Him,"Hey buddy, I might need your input. The girls in the office are saying the A/C isn't doing anything and they can't even feel any air moving. There's a little drip coming from the return air side too."
I immediately thought of this thread, lol.
Me, "When did you change the filters last?"
Him, (sheepishly grinning), " Oh, probably a long time. Maybe 2 years or more."
Me, "The coil is likely frozen because the filters were filthy. Grab your 5/16 nut driver and impact and we'll take the cover off and look."
Up to the rooftop we go and lo and behold, here's what we find. Can't even get the filters out until it thaws.
 

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