OT: Need Home A/C Help, Evaporator Coil Keeps Freezing Up Options

[thomasotten]

My Home Air Conditioning unit keeps freezing up. The indoor coil gets totally frozen with ice, and so no air flows through anymore. I had a friend help my check the freon and and it had 60 psi, and he said that it was fine on freon. What's causing the indoor coil to freeze up?

[seanery]

there's gotta be a small leak somewhere. I had the same problem

[type47fan]

Iced up indoor coils usually can be traced to an airflow problem: clogged filters or a restriction/blockage in your return air ductwork. Check your fan, also. A failing indoor fan motor can't move enough air to keep the coil from freezing up. Good luck.

[phantom914]

(IMG:style_emoticons/default/agree.gif) Also could be the evaporator fins that's clogged if it was run witout a filter or the fiter was not sealing. Is this a new system that did this right off the bat, or is it a system that you've used for a while and always worked fine until now?

Andrew

[thomasotten]

About a 5 year old system.

[gopack]

Had the same problem. turned out it was a 2 speed fan set up and the relay had failed, so at low loads it wsa ok, but at high loads it froze up.
good luck
mark

[Bruce Allert]

Is this a window unit? My condensing unit is outside. This is a unit attached to the forced air gas heating unit. Coils are outside.

I had a window unit that would freeze up and the coils were inside. Usually this was caused by the unit being too small for the required cooling and the day was too hot which did not allow the unit to catch up or completely cool the house to the desired setting. I also thought it was a coolant problem....... but NOT!

.......b

[phantom914]

About a 5 year old system.

Then check all of the above.

Andrew

[MarkV]

I have a rental that does this if I use a pleated filter. The HVAC guy told me that the house doesn't have a big enough cold air return for the size of the A/C unit. If I run the cheap $.59 fiber filters I don't have a problem.

[Don Wohlfarth]

2 most common problems for icing evap coil, low on refrigerant, low air flow. Since the system has refrigerant it may be low air flow. If the filter is not changed regularly or system is run without filter you may have evap coil clogged/matted with dirt. With system operating (and proper refrigerant charge) you want a 16-17 degree temperature split accross evap coil (entering air versus leaving air).

[SpecialK]

Actually your buddy is wrong about the 60 psi on the low side being okay, in fact depending on the outside temp., 60 psi is about the perfect pressure to turn your evap into an ice maker. Assuming that your coil (evap) and air filter is clean, 68 - 72 psi is more along the lines of what you'd want on the low side (I know, it doesn't seem like much, but it makes a difference). What's happening is that your freon is flashing/boiling off too soon in the evap. coil causing the moisture in the air to freeze rather than condense. As the ice forms it creates kind of a vicious circle 'ice--less airflow--which creates more ice--which reduces the airflow further--etc. What you want for a temp. differential between the return and supply is 16 - 21 deg. F, anything either side of these temps will either freeze your coil, or be insufficiently cold to condense the moisture in the air (which is the main purpose of A/C -- "It's not the heat, it's the humidity"). If you're lacking a superheat gauge to service the A/C, PM me and I'll give you an "Old Timer" method to get it reasonably close to 'on the money'.

p.s. - Be sure that your coil is completely defrosted/iced prior to servicing. Quick way, crank up the furnace for 15 - 20 mins., preferred way, turn your T-stat to "Fan-on" and the "heat/cool" switch to "off" and let it run until no more water comes out of the drain.