Hot Topics: Frozen AC Unit

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Original Post: AC not cooling, ice build-up.

m4gnum - Member

Hello. My "Trane" AC was not cooling since yesterday. I noticed that there is water dripping from the indoor AC unit onto the floor, I checked the filter and it is soaked in water. There is lots of ice build-up in where the filter goes. I attached a picture.

What is the cause and solution?

Thank you!

an ac unit with icy build-up

roughneck77 - Member

It’s either a refrigerant or air related problem. Is the blower running?

Bob14525 - Member

As roughneck stated, an iced up evaporator coil is usually caused by either insufficient airflow across the coil due to a dirty filter or bad blower motor, or by insufficient refrigerant in the system.

After the ice has melted, try turning on the fan (blower). If the airflow feels "normal", then you are likely low on refrigerant and you should call in a technician to diagnose the problem (system is leaking and the leak needs to be repaired).

m4gnum - Thread Starter

I noticed that there is a hissing/bubbly sound coming from the refeigerant coil right at part where its connected to the unit, when my AC got frozen last time.

Now, I let the ice melt and the coils dry out, than replaced the filter with a new one. The AC worked for 3-4 hours and suddenly I heard an airy hollow sound and than a pouring water sound (similar to toilet flush) and AC turned off. The water is dripping from the unit again.

I returned to the same issue as before, the coils are frozen. I was happily falling asleep at 76 degrees and I think were back to 87 as when it turned off last time

I will check the airflow from vents tomorrow.


I would say the charge needs to be checked.

m4gnum - Thread Starter

I took out all the unit covers to clean the evaporator coils but it looks very clean from the upper side.

The only thing that is pretty dirty is the yellow sponge/foam that is next to the coils.

ac unit with rust spots

What cost would I be looking at? It's a 22 yo AC so I assume it runs on R-22.

roughneck77 - Member

That’s the insulation for the drain pan for horizontal installs.

It will list the refrigerant on the indoor and outdoor unit.

Bob14525 - Member

As you're probably aware, R22 is being phased out. Production of it stopped years ago, so the price has been rising every year. You'll have to weigh the cost of finding the leak and repairing it plus the cost of the R22 against the cost of a new R410A system. I'm in a similar situation.

My R22 system is approximately 25 years old. Fortunately, it is still working, however when it does fail (leaking refrigerant), I think it will be more cost effective to replace the system. If you spend several thousand dollars to repair the old system, there's no telling when it will leak again from a different place.

AllanJ - Member

Is the drain hose on the evaporator clogged so water pools up? If the filter(s) get soaked then air flow is impaired and then things can freeze up more quickly.

m4gnum - Thread Starter

I had a service call and they said that there is no refrigerant, they said that they can fill it up for $200 but it is going to leak anyway. They stated that the AC needs replacement because its too old. They asked $4700 for a new AC system.

I am waiting for another company to take a look at it today.

I also found out that there was a major job done in 2011 worth almost $4000. They replaced all ducts and recoiled the air handler. That would mean that even though the AC is old, the components are not that old.

Would you recommend replacing it or repairing (having in mind that it had a $4k repair done 8 years ago).

roughneck77 - Member

At 22 years old I wouldn’t spend much money on it.

But they could throw some nitrogen in it and spend an hour looking for the leak to see if it’s something simple.

m4gnum - Thread Starter

My happiness did not last long. There was water dripping from the air handler every few seconds. Now the AC shuts off every 30 seconds and spills lots of water right after shutting off.

It's not freezing anymore though.

What could that mean?

Should I get my money back from the contractor or have him look for the leak?

roughneck77 - Member

It’s probably starting to freeze. Or you have a condensate overflow switch and your drain is clogged.

Could mean you have a large scale leak though.

m4gnum - Thread Starter

Just one more thing that I noticed, this is not a 100% reliable information but it worked with every try so far.

The AC shuts off and spills water only when I switch Fan Mode on thermostat from "On" to "Auto". Just try two different variations and it worked that way every time.

When the AC unit was freezing the Fan Mode was switched to "Auto" as well.

During the day, before the HVAC guy filled it up with refrigerant, the thermostat Fan Mode was switched to "On" and the AC was working until todays evening when I switched it to "Auto".

Is this something that might be a cause?

Maybe I'm just oversensitive about that AC now but I think that the fan wasn't as loud as it is now. Or maybe it just wasn't constantly running as it was always to switched to "Auto" position.

One more thing is that when the "cooling" mode turns on, the air handler unit makes a hissing sound, maybe a little bit bubbly. It's the same sound as when you turn on gas heater.

hvac01453 - Member

Have a tech recover what refrigerant you have in a clean tank down to 10 psi. Then pump it up with nitrogen to 150 psi and leak search this unit with an electronic leak detector. Repair the leak. Pressurize the system overnite with 150psi nitrogen to leak check it.

If ok, pull a deep vacuum and weigh in the charge using the recovered gas and then finish the balance of missing gas, with fresh gas (refrigerant). If the leak is too hard to find, have the tech inject dye into the system, with its charge, and give it a few days to leak out and show him all the leaking areas. Clear the condensate drain from the pan, down to its outlet.

When the fan switch is in auto, the fan shuts off when the demand is met. If that switch is in the on position, the fan runs continuously. This has a tendency to balance warmer and cooler rooms to an average temperature. It also melts any frost (not ice) accumulation on the evaporator coil, during the off cycle. Make sure all your returns and outlets are open also.