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Air handler freezeup

Thanks Stephane, it did seem odd that the system was cooling slow from the time he was done with the repair. It is now cooling very well. Another new thing I have noticed. The Economiser is working again. I think that the system was gradually loosing freon and cooling ability. If it was not able to cool enough to satisfy the sensor in the main duct it would call for the modutrol to stay fully closed. Gotta love it. T.


  • thfurnitureguy_4
    thfurnitureguy_4 Member Posts: 398
    frozen coil in air handler.

    The Tech was out fixing the leak in my system on Monday. The leak was found in the large line (3/4") at the compressor. There was a strainer in this line that the tech. said was used in the old days along with the one in the smaller line (I think this is the Line dryer). He removed the strainer, and replaced it with a new piece of pipe (no strainer). The smaller line was left alone. After recharging the system it started cooling. Seemed to take a long time to cool down (7 hours) it was within a degree of satisfying the stat. It shut off from the program. I assumed it was hot and the bldg. was storing heat. Anyway, today the Air handler was frozen up and the compressor was off ( I assume it tripped on heat). This is what I see that looks wrong or strange. The insulation is missing on the big line where he fixed it. About 15" is missing at the compressor and as the line goes down to the air handler has sections half missing in places. The filter set up looks modifyed over the years. It has a large wire setup looks like 2 sections of cage about 2' cubes set side by side. If filter cloth / paper were threaded into it it would make a fan fold filter. The cage is still there but there is no cloth/ paper in it. In front of the cage is what looks like a grease filter that you would see on a range hood. They cover the whole opening, 2- about 24" sq. infront of these are the fiberglass filters (look more like the furnace filters I'm used to) The metal filters were washed out and the fiberglass filters replaced last week. The question: the expanded aluminum grease type filters seem to have alot of air pulling on them, when you take them out to clean them. My thought was to remove the expanded metal filter and use just the fiberglass ones to see if the system would stop freezing up. I hate to call this guy back if it is somthing stupid like a filter. Anything you can tell by the above symptoms that would make the thing freeze? My thinking is that poor air flow through the coil in the airhandler might cause this. The Tech checked all of the wiring and saw nothing that looked messed with in the Hi voltage, and the control wiring looked good to him. He said that the strainer would cause a line restriction. Could the lack of this restriction cause the freeze up? I would like to understand this more fully before I call him back out. Thanks for any thoughts on this.
  • Eugene Silberstein
    Eugene Silberstein Member Posts: 1,380
    Freezing Evaporator Coils

    Here is a list of causes for evaporator coil freezing:

    Dirty or blocked evaporator coil

    Dirty or clogged return air filter

    System undercharge

    Blocked return duct

    Damaged return ductowrk

    Closed supply registers

    Loose duct liner

    blocked or covered supply registers

    Defective blower motor

    Improper belt/pulley alignment

    Dirty squirrel cage blower

    Improper (too low) blower motor speed

    Loose or missing access panel on the air handler

    Underfeeding metering device

    Liquid line restriction

    A lot of these items can be verified and eliminated quite quickly.
  • thfurnitureguy_4
    thfurnitureguy_4 Member Posts: 398

    I have checked the list and other than the < loose duct liner??? It is tight and clean. All of the registers are wide open and there are no restrictions or missing panels. Should the dryer in the small line have been replaced when he opened up the system?
  • don_120
    don_120 Member Posts: 15
    And one more

    The intermitted fan delay relay.
  • thfurnitureguy_4
    thfurnitureguy_4 Member Posts: 398

    This was a surprise. I turns out that after the repair was done and the unit was refilled the Schrader valve was BLOWING freon. OK im not a tech but if I filled a car tire and the tire was blowing air through the valve when I removed the chuck I think I would have noticed a problem. It is odd that the safety caps didn't hold past a day. They pumped down the system again and are Installing new valves. Yes these are the costs of fixing old junk. I can just feel the I told you so. BTW What is a duct liner?
  • Jon_10
    Jon_10 Member Posts: 47
    duct liner

    fiberglass batt glued to inside of duct for noise reduction and insulation.
  • Stephane Gautreau
    Stephane Gautreau Member Posts: 2
    It's always the schrader!!!

    As long as I can remember, techs have been blaming schraders for leaks. The fact is schraders that leak usually don't leak past the cap, and if the cap does leak you would only loose a couple of onces a year.
    It sounds to me like he didn't properly charge the unit the first time and had to add some more refrigerant. OR He didn't fix the leak properly OR there was more than one leak.
    As far as the strainer on the suction (big) line, it usually gets installed after a compressor has burned out and should be removed shortly after the unit has operated for a while. The small lenght of insulation that has been removed is not cause for concern unless the pipe is inside where water damage can occur.
  • soot_seeker
    soot_seeker Member Posts: 5
    that's not how it works...

    the economizer is probably working again because it's been a little cooler here on the east coast & in PA - especially in the morning & night now. that sensor just checks for cool air roughly under ~73F coming into the evap coil - if the entropy module is a simple drybulb type & the air temp is around 70F or so - and assuming the the control is turned more to setting A rather than to B, C, or D (almost (D)isable) - then it will open the damper to provide free cooling and - depending on the mech cooling disable jumper - either disable the compressor simultaneously or (if not disabled) will run the free cooling in tandem with the mech cooling. that's it.

  • jeff_51
    jeff_51 Member Posts: 545
    have replaced MANY leaking schrader valves

    I just replace the core everytime I work on a system, and those caps, even with the "o"rings don't hold. They are really just to keep out dirt. I don't know why anybody has tried to sell them as leak proof. If they are, you are just lucky.
  • thfurnitureguy_2
    thfurnitureguy_2 Member Posts: 74

    These valves were weard. The tips where the valve core would come out were peaned over some what, to where you could not just screw them out. I think he drilled, soldered and replaced with a new set. I'm glad he stuck with it. It seems to be working just in time for winter. LOL
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