I am trying to determine what is wrong with my central A/C unit. The 11 year old TRANE XE1000 worked fine until today. The unit did not put out cold air and I noticed that the refrigerant line and the compressor had quite a bit of ice on them. I removed the covers on the outside unit and cleaned the fins with a garden hose. The outside unit was a little dirty but I have seen much worse. I checked the drain pipe for the inside A coil and it was clear. I turned the unit back on and the unit came on but the air flow from the blower was reduced and the air was warm. The filters are new. The outside compressor was running. The inside furnace and A coil were last replaced in 1992. I did notice a tiny bit of water in the back floor of the furnace. I should mention that I recently had trouble with the Honeywell Chronotherm III thermostat (the plastic tabs that hold the backup batteries broke recently and I sometimes have to wiggle the the thermostat to get it to work. Could these all be separate troubles or are they intertwined problems? Any Help would be appreciated.
Thanks
Stan
Replies
Probably the evaporator coil inside the air handler unit had iced up. This can occur due to either reduced airflow or a loss of freon in the system.
Turn the AC off and let it sit for about 2-4 hours, but, if possible, leave the thermostat on "fan". See if the fan volume improves after ice in the air handler has melted.
Reduced airflow can be due to clogged filters (double-check them), too many registers blocked off, or having the fan running at the wrong speed. Do you need to manually switch the fan to high speed for cooling season?
It's unlikely that the thermostat could be the problem, but it's vaguely possible that it could affect fan speed.
(Well, actually it's highly probable that one particular scenario with the thermostat could be the problem: The "cool" and "fan" wires from the thermostat are separate, and when the thermostat "calls" for cooling it's supposed to put voltage on both. If it only put voltage on the "cool" wire then the fan wouldn't run and the evaporator inside the air handler would ice up. So leave the thermostat "fan" switch on and see if that helps.)
DanH:
Thank you for the answers. This is an old 2 1/2 story house and the 2nd floor is not in use, therefore I have closed off all of the registers on the 2nd floor. We only use the A/C two days per week. I will leave the blower fan turned on and open the remaining registers. The blower was a variable speed unit but it is set to only run on one speed. I had planned to replace the thermostat anyway but my hvac repairman previously told me that the older Chronotherm III units were made better than the new ones.
shoot the padlock off your wallet and HIRE someone who can solve your problem.
Best thread I've gotten advice on BT was hire the best no matter the price. Did that and just turned on my HVAC system on for the first time last week. Best advice I've ever gotten from BT. In short, he 100% correct. Shoot the lock off your wallet
Edited 5/16/2007 8:45 pm ET by curley
Curley:
This is not a matter of being cheap. I have a problem taking time off from work for the next two weeks and in addition to that issue, my wife and I run a new small business so there is not a lot of time to schedule a repair visit.
It's worth a shot at least to let it defrost, open all the registers, and have another go at it. Worst case you'll have to call the repair guy to diagnose and possibly leak-check and charge the unit.Do be wary of the flaky stat -- if a stat causes the compressor to cycle off and on rapidly it can damage the compressor.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
do you have a manifold, guages etc? Do you have mep gass torch and some copper? You can try to determine all you want but eventually someone will have to come out.
fyi- many units have high pressure switches on the outside units that can rust out over time, in fact they have alot of bells and whistles that can rust out over time. On my unit it was the high pressure switch that leaked the refrigerant.
-worth exactly 2 cents!
it is one of two things. first it is low on freon,this will cause the a coil to freeze up like a iceberg.
but the next thing is airflow acdoss the a coil. you say the fan is on one speed ,if that is not high speed there is your problem,not enough air. next you say you have all the upstairs vents close,another problem. the fan must blow a certain amount of air to kee p it from icing. so either open the vents or you may even take the regerstars off down stairs so max air flow can happen.
now those are the things you mentioned ,look at return air,has someonen moved a couch over a return air vent?
keep your wallet shut until you have looked at the simple things first. larry
hand me the chainsaw, i need to trim the casing just a hair.