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  1. #1

    Frown Evap coil ices-over

    I'm trying to troubleshoot my 12-yr old Trane heat pump unit that has a problem with freezing-up the indoor evaporator coil. The unit is the first-level zone of a two zone system with the evaporator/blower in the basement and the condenser/compressor outside. During the winter, a local HVAC contractor installed an AprilAire humidifier into the ducting with a by-pass installation. I turned the AprilAire off at end of the winter. When I turned-on the cooling side of the heat pump, within 6 hours, the indoor evap col iced over. Th eblower was still blowing but there was no air flow. I tuened off the system and thawed the evap coil, cleaned the coils carefully, put in a new filter, and in approx 6 hrs it will start icing the coils again. The blower motor works fine and was replaced a year ago. In addition, when the evap coil ices-up, the refrigerant line (covered in black insulated foam) going out to the outside condensor starts sweating like crazy.
    What is happening? I have good air flow past the evap coil (when it's not iced-over). Help?

  2. #2
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    The humidifier should have a bypass damper; close it.

    Thaw the coil, change the filter and open all registers. If problem persists, call a technician to check the indoor coil and refrigerant charge.

  3. #3
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    Something a pro should diagnose. Sounds like it has airflow problems (return side) or is low on refrigerant.

  4. #4
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    Quote Originally Posted by RyanHughes View Post
    Something a pro should diagnose. Sounds like it has airflow problems (return side) or is low on refrigerant.
    The fact that a humidifier was installed is a clue. An open bypass damper could ""short-circuit" enough air the freeze the coil if airflow was marginal to begin with.

  5. #5
    Thanks. I had also closed the by-pass duct damper on the AprilAire unit. So there shouldn't be any unwanted humidity cominhg-in from that unit.

    I have only the blower back on now to the hasten the thawing of the iced-coil.
    Could the new blower (put in over winter) be mismatched for the unit? I believe some Tranes have a two-stage blower with low-high speeds. I'm wondering if the replacement blower is a single speed and is simply not moving the air past the evap coil fast enough to keep it from icing.

  6. #6
    Just FYI...I removed the AprilAire cover and couldn't believe the amount of air still being pulled past the AprilAire damper by the blower motor. So even with the AprilAire humdifier damper closed (in the "Summer" position), the airflow was significant and by-passing the evap coil.

    So I jury-rigged a cover over the by-pass damper itself to stop all by-pass air-flow and have switched the cooling back on. Hopefully, this fix will increase the necessary air-flow over the evap col and it won't ice over.

  7. #7
    Join Date
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    I would still have a tech come out to take a look at the situation and give it the all clear.

    If you have a problem, the quicker its diagnosed, the less damage that results.

    Also, if you don't already, get on a service contract for the system. It will improve your systems performance and in turn, hopefully extend the life of the equipment.
    I fully support the military and the War on Terrorism.


    If you don't know, then don't do. If you don't know and still do, then be prepared to pay someone else a lot to undo what you did and then do it right.

    If you do know, then do. But do it right. Otherwise, you may not be doing it long.

  8. #8
    Yep...roger that. The fellow who installed the AprilAire is coming tomorrow to relook the install and check the charge. Meanwhile, good ole 100 MPH tape over the faulty damper to plug the air leaks has me back on-line.

    Thx for your mil service. I am Ret-Army, Ranger. Those that criticize the GWOT don't know the on-the-ground truth and successes. Simple as that.

  9. #9
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    Quote Originally Posted by Red Ranger View Post
    Thx for your mil service. I am Ret-Army, Ranger. Those that criticize the GWOT don't know the on-the-ground truth and successes. Simple as that.
    ditto. Been there..............Done that...........got the T-shirt.
    I fully support the military and the War on Terrorism.


    If you don't know, then don't do. If you don't know and still do, then be prepared to pay someone else a lot to undo what you did and then do it right.

    If you do know, then do. But do it right. Otherwise, you may not be doing it long.

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