Icing indoor coil
Have a 2 ton AC system were the indoor coil freeze into a block of ice. We've checked the air flow and it looks to be on the low side but changing duct-work is not possible. Have heard about a temperature switch that can be installed inside the AH to measure air temperature and stop the outdoor unit until the air coil deices. Anyone done this and where and how did you mount it?
Have you checked your charge and filters?
There are many things that can attribute to an icing coil.
2 ton only requires about 600 cfm to prevent icing. That isn't much. What are your SH/SC numbers? Can your change the fan speed?
Freezestat
I agree with MEPlumber. I'd check those areas first. If all else fails, you could put a disc type freeze-stat on the suction line at the coil. I'd also put it in series with a time delay to prevent short cycling.
Bob
You can choose to do what you want, but you cannot choose the consequences.
COIL ICING UP
First of all, have you checked your delta t across the coil.
Second what size return do you have and a two ton requires 800 cfms of air
Third what size is your return air( duct work and face grill min 20x 20 face grille ad min 12 inch return duct) and is this a matched system, have you checked your blower motor, have you checked not just the front side but the back side of the coil. It is not normal for a unit to just freeze up. If it was in a small room where ac was needed year around yes if you didnt have low ambient control of some sort, but just to put a freeze stat is not gonna fix your problem it may hide the real problem.
Juice?
What's the refrigerant level like? Freezing up often is low charge.
Not All Frozen Evaporators are the Same!
So many technicians run to get the tank of refrigerant from the truck when they see ice on an evaporator coil. Before you become one of them, read on.
Before adding refrigerant to the system, be sure to evaluate the pattern of ice on the coil. If the coil is frozen solid, chances are that a refrigerant undercharge IS NOT the problem. However, if you notice that only the first one or two passes are frozen and the rest of the evaporator coil is warm, you are likely dealing with a refrigerant undercharge. You can also be dealing with an underfeeding metering device, clogged liquid line filter drier or damaged liquid line as well.
If there is an airflow problem through the evaporator coil, the amount of heat being added to the refrigerant will be reduced and the temperature of the entire coil will drop, causing it to freeze solid.
If there is an undercharge, the saturation temperature of the refrigerant in the evaporator coil will drop, forming ice at the inlet of the coil. But, since there is a refrigerant undercharge, the evaporator superheat will rise considerably, making the remainder of the evaporator coil warm.
Enjoy your summer!
Eugene
Gene, Great points.
As you know by the time we get there it has been cycling for 1 billion years........Exaggerating,.... So the info you give will only result from a somewhat fresh start. The ice will build and compound itself due to the remaining coil area not yet frozen and result in the beer cooler scenario.
Air flow is also important and can play a roll in this problem, but let's see what other facts can be provided.
Great to talk to you again Geno.......
Mike T
Empire Mech.
You are Correct Mike!
You are correct Mike,. Your input is always appreciated.
I hope your summer is going well!
Eugene
Also.
A frozen suction line is usually the first good sign that you have an airflow problem. A restriction in any part the circuit will usually frost over at the site of the restriction.
