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Frozen evap coil and covered with some kind of black spongy material

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Rome says:
May 24, 2011 at 10:27 am

1993 house with I assume original heat pump AC system. Started making gurgling noises in the attic and quit blowing.
Found evap coil frozen and covered with some kind of black spongy material that looks like it has been through a shredder.

What is this stuff? Where did it come from? Is it something that will require replacement? Any recommendations on how to clean it out? It gets between the coils very easily when trying to remove it and isn’t coming out very well with a vacuum or brushes.

asked in Cooling System by darekrudy (21,730 points)
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1 Answer

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Hi Rome,
If it looks like it has been shredded it most likely have come through the return air duct of the air handler and it was shredded by the blower. What is it… I’m not sure, spongy appearance would suggest AC refrigerate line insulation or insulation from the interior walls of the air handler. In case your blower is belt driven this material could be from the belt itself… I don’t know how much of it there is.

There is a possibility that something was inside the air duct and it was sucked into the blower compartment… If you have a drip pan underneath the air handler use the coil cleaner (search for “ac coil cleaner”) and rinse the coil with water after using the cleaner (unless otherwise specified in the cleaner’s manual). You may want to put some plastic foil underneath to prevent ceiling damage below.
answered by darekrudy (21,730 points)
Rome says:
May 24, 2011 at 12:45 pm


thanks for the reply.
This stuff is on the return air duct side of the coil with no way to pass through to the blower from best I can tell.
No belt driven blower either. The black stuff covered about 3/4 of coil that is about 15?x25?.

I think you are probably right about it being copper pipe insulation. The system has a drip pan so I will find and try some coil cleaner you recommended. As for the ceiling damage, I am not too worried about that at this point.

I have a bad knee that gave out when I stood up after trying to clean this gunk for about twenty minutes and I lost my balance and stepped through the ceiling with one leg.

Sorry about the accident Rome, I hope you’ll get well soon. If it is inside the air return duct, it would have to go through the blower in order to reach the coil…
Air conditioning system air flow

Rome says:
May 24, 2011 at 3:01 pm

thanks for the wishes, the knee is doing well.

ok, please have some patience with me while I try to understand.

Looking at my system which to me is lying horizontal. I have an air duct coming in on the left end. Then there is the filter, then the evaporative coils, then what looks like some kind of heating elements, then the blower motor blowing to the right into the duct.

My blower does not blow accross anything? Is this a different kind of system or what?

thanks again,
I’m puzzled… those heating elements suggest that it is an electric heat or just a supplement (backup) if you have another gas / oil fueled heating system.

However, for the system to function properly the air needs to be forced through the coil and the heating elements / not pulled through them. I’ve never seen such design… It’s kind of up side down. Are you positive about the air flow direction?
Rome says:
May 25, 2011 at 2:27 pm


I am going to verify flow through my system tonight and install a new blower motor. I tried to find a picture online of my system but no luck. My system is a heat pump type and I have no other system for heat.

In the meantime, I took my old motor in for matchup to buy a new one and everything matches except the amperage.

1075 RPM
3 Speed
1/3 H.P.

My old motor is 2.1 A and the new one is 3.1 A. Did they make a mistake or does that amperage difference not matter?

Hi Rome,
Those heating elements usually kick in when the ambient temperature drops below 50F or around that temperature. That’s where the heat pumps stops being efficient.

For the motor’s amperage; I think it should work except for whatever overload protection there’s installed. If it’s fused for the lower amperage and the motor will draw close to its rating, it might blow that fuse, trip the relay, etc.

You’d have to contact heat pump’s manufacturer and confirm with them.

thanks for the amp info. The flow through my system is correct as I posted earlier with one exception. The heating coils are right of the blower.
So again, left to right:
Return duct, filter, evap coils, copper lines, blower, heating elements, outgoing duct.

The bad news is I have installed a new blower motor and it doesn’t turn either in auto AC or fan switch on.
Called the AC guy who will be out today. He said it is probably a bad circuit board.

This is not going well:
3 days of no AC
hole in my ceiling
injured knee
money spent on new motor & cap and old one may not be bad

I am glad I found your site and got your help though. That has been the only plus from all this.

Any time Rome, Thank you!