I fixed it! [but I don't know how!]

[WanderALot]

I woke up at around 3 am this morning and it was pretty warm in the room even though the A/C has been running all night. It felt like there wasn't enough air coming through the registers. So the first thing I checked was the filter which was just replaced less than 20 days ago and it looked fine. I went outside and noticed a sizable chunk of ice on the A/C unit, indicating that there was some sort of blockage someplace. After this professional diagnosis I figured I'll get up in the attic and poke around. Spent about 15 min without knowing WTH I was looking for, except for some obvious duct work that had burst open. I didn't find anything was ready to give up and call the A/C guy tomorrow.

I turned the fan on again just to see what would happen and all of a sudden, it appears that the air flow is back! Now, the A/C's seems like it's working great, but I can't sleep and have to get up in about 2 hours to go on a run with DW. Which would be fine, except for I don't have the satisfaction of knowing that I did something to fix the problem.

I'm going to bring this thread up during the next "rent vs. buy" thread.

So any guesses as to why the air flow was blocked? Everything seemed fine last night when we turned on the A/C.

 

[mathjak107]

icing is a sign you are slightly low on refrigerant usually, the coil temp usually should be around 45-50 degrees but if you are low on refrigerant the system pressure drops also dropping the coil temp. once the coil gets to 32 degrees it ices up. although the coil runs cooler you have less cooling capacity because you have less refrigerant in the system so its not a good thing.. i know you were thinking if im low on refrigerant why is it running colder....

if your going to try to add refrig yourself make sure you get no air from the hoses into your system.

 

[WanderALot]

icing is a sign you are slightly low on refrigerant usually, the coil temp usually should be around 45-50 degrees but if you are low on refrigerant the system pressure drops also dropping the coil temp.. although the coil runs cooler you have less cooling capacity because you have less refrigerant in the system...

But how would that affect air flow? Especially since air flow was restricted even when just the fan was on (A/C off).

 

[mathjak107]

the coil starts to freeze and eventually the air flow cant go thru, it has to defrost..it will do it again if humidity and temperature are right, its not fixed you only defrosted the blocked coil

 

[FIREd]

Yes, it happened to me a couple of years ago. Low air flow, no cooling. When I opened the unit, the whole coil was encased in ice, hence the air flow constriction. We had a small refrigerant leak in the coil which lead, overtime, to a drop in pressure severe enough to allow ice to form around the coil.

So the problem is not fixed. First you need to add refrigerant to the system and second, you need to find out why the refrigerant pressure fell in the first place. You probably have a leak somewhere.

 

[Walt34]

I agree, probably a leak in the system. Eons ago I worked as a heating & A/C repair tech. The electronics and refrigerants have changed but the physics have not.

There is almost certainly a slow leak in the system. If it does ice up again you definitely have a leak. It is not a do-it-yourself job because the tools required cost more than having it done. The vacuum pump alone was $500 in the '70's. That is needed to purge the air (and the moisture in it) from the system before filling it with refrigerant.

Also, I think now a certification is required to buy and handle the refrigerant because the old stuff has to be collected instead of just vented to open air like we did in less environmentally enlightened times.

 

[kumquat]

I went outside and noticed a sizable chunk of ice on the A/C unit, indicating that there was some sort of blockage someplace.

Did you have ice on the cooling coil in the ductwork/furnace or on the compressor?

Our coil (in the ductwork just above the furnace) used to ice up to the point that air flow was cut off. Then when it melted we had water all over the place under the furnace. You might want to check for water under your cooling coil.

 

[WanderALot]

Thanks for all your help everyone! I think I might have misled people when I said ice on the "A/C unit". I meant the compressor outside, not in the cooling coil inside (which, to be honest, I haven't checked). Thanks kumquat for making me realize the ambiguity of my statement.

Does the diagnosing of a refrigerant leak still apply? As I said earlier, I don't understand the ice (on the compressor) would affect my air flow when just the fan is running. Hope this isn't a dumb question!

Thanks.

 

[FIREd]

Thanks for all your help everyone! I think I might have misled people when I said ice on the "A/C unit". I meant the compressor outside, not in the cooling coil inside (which, to be honest, I haven't checked). Thanks kumquat for making me realize the ambiguity of my statement.

Does the diagnosing of a refrigerant leak still apply? As I said earlier, I don't understand the ice (on the compressor) would affect my air flow when just the fan is running. Hope this isn't a dumb question!

Thanks.

It still applies. When I had the refrigerant leak, I had ice building not only around the coil, but also around pipes carrying the refrigerant between the coil and the compressor (in places where the pipes were not well insulated), as well as outside, near the compressor itself. Do you have water coming from underneath the coil? I know I did when the ice around the coil started melting. At any rates, you should probably check the coil for ice. I think it's the reason why you have no air flow.

 

[mathjak107]

the lower the pressure in a sealed system the lower the equivelent temperature. normally you charge an ac unit so the line sweats back to the compressor when touched with your hand.. when there isnt enough refrigerant in the system the pressure is lower and the outside of the tubing drops below freezing... instead of sweating things ice up.

if its not the coil also icing and only the suction line freezing then you have another problem like below .

sometimes whomever charged the unit last may have introduced air into the system too. air has moisture. if the system gets slightly low on refrigerant again the pressure drops and the moisture in the air now freezes and blocks the flow of refrigerant thru the tiny orifice of the metering device.. when you shut the system and it melts all goes back to normal but should the moisture in the system freeze again the flow of refrigerant will stop too.

the system will have to be leak checked, evacuated with a vacuum pump to get the air out and refilled.