1. Attention: We have put together a thread with tips and a tutorial video to help with using the new software. Please take a moment to check out the thread here: Trapshooters.com Tutorial & Help Video.
    Dismiss Notice

Central a/c help

Discussion in 'Off Topic Threads' started by mixer, Sep 11, 2012.

Thread Status:
Not open for further replies.
  1. mixer

    mixer Well-Known Member

    Joined:
    Jan 29, 1998
    Messages:
    3,386
    Location:
    Coral Springs, Florida
    Central a/c freezes up sporadically, about once every 7-8 days and only overnight. System runs fine all other times. New filter, condensor is clean, right amount of "freon" in system. A/C repair service is stumped as everything checks out. Any ideas?

    Eric
     
  2. wayneo

    wayneo Active Member

    Joined:
    Jan 29, 1998
    Messages:
    3,002
    I can only think of three things, your evaporating (A) coil is really, really dirty and needs blown out, low on refrigerant, or your fan inside is not running or is running on the low speed setting for heat. As the humidity goes up at night is the condensation inside your unit draning properly? A dirty A-coil will freeze the condensation.

    Wayne
     
  3. ScottEslick

    ScottEslick Member

    Joined:
    Aug 5, 2009
    Messages:
    351
    Location:
    Waynesboro, PA
    What Wayne said, how are the temps at night when it freezes? What temp do you keep your thermostat set?

    Scott
     
  4. Ljutic111

    Ljutic111 TS Member

    Joined:
    Jan 20, 2008
    Messages:
    1,730
    What Wayne said .
     
  5. mixer

    mixer Well-Known Member

    Joined:
    Jan 29, 1998
    Messages:
    3,386
    Location:
    Coral Springs, Florida
    I guess no one really read my original posting.

    Eric
     
  6. Catpower

    Catpower Molon Labe TS Supporters

    Joined:
    Jan 29, 1998
    Messages:
    10,253
    Location:
    In the Cabana
    Put a Motor Master or head master on it to keep the high side pressure higher in the low ambient at night

    What is the temp differential across the evap coil?

    Wayne has given the normal things that cause a unit to freeze up
     
  7. Harv Shell

    Harv Shell TS Supporters TS Supporters

    Joined:
    Jan 29, 1998
    Messages:
    1,865
    Location:
    Morris, Il.
    Eric, need the following info to make a reasonable guess. Ambient temp(outdoor), indoor temp, low & high side pressures, fixed orifice or txv coil, R22 or R410A and as Cat said temp split between supply and return air temps measured close to the unit. Harv
     
  8. cmptrwz1

    cmptrwz1 TS Member

    Joined:
    Jan 29, 1998
    Messages:
    165
    There is a small thermol switch on the condensor line just past the compressor. If the system freezes, the switch is used to single the control panel and turn off the pump and reverse it to run in opposite direction and the hot gas from the house is used to unfreeze the unit. When it hits the right temperature, it shuts down and goes back to normal. I had one go bad on my unit and that's what it was, the switch looks like a little silver clamp on can, about an inch or so in diameter with two wires coming out of it and goes to the control panel on the outside unit which controls the compressor.
     
  9. Catpower

    Catpower Molon Labe TS Supporters

    Joined:
    Jan 29, 1998
    Messages:
    10,253
    Location:
    In the Cabana
    Cmptrwhz, I guess that stands for computer whiz, you probably ought to stick to it, because a defrost termination thermostat doesn't have anything to do with the indoor coil freezing up
     
  10. grntitan

    grntitan Well-Known Member

    Joined:
    Mar 25, 2009
    Messages:
    17,230
    Location:
    IL(The gun friendly Southern Part)
    I don't know jack squat about them but when mine froze up, the AC man said it was low on coolant and the PVC drain pipe was partially clogged with rust(which he warned to get ready as she is self destructing). Of course he could have been full of crap too but it worked and hasn't froze up since then. Never fails that mine freeze up when it's a 1000 degrees outside. Anyone else have that luck?
     
  11. cmptrwz1

    cmptrwz1 TS Member

    Joined:
    Jan 29, 1998
    Messages:
    165
    Well Catpower you sound as you are the great A C repair person with your reply to the stated post he didn't state what unit was freezen up in the frist place and throwing money for un needed part is the way to go.I told him what to check with ohoms meter and that doesn't cost nothing and if it is the inside unit that is freezen then it could be only one of two things but I will let you figure that one out for yourself. Buy yourself a good A C book and see how a A C system works and you my figure it out for yourself and by the way what does Catpower stand for ,that your head is stuck in the litter box all day.Happy Trails our should I say keep on digging.
     
  12. wayneo

    wayneo Active Member

    Joined:
    Jan 29, 1998
    Messages:
    3,002
    Well Mixer I read your original post, so did everyone else. You ask for some help and we offered. If your AC tech says everything checks out ok......Then what you need is a new AC tech. BTW a clogged or crimped capillary tube,or a stuck TEV is where the problem could be. But a competent residential repair man could see the frost build up on the inlet of the evaporator coil and sees how far the frost travels. Jeez..... ask help some where else.

    Wayne
     
  13. X Trap 2

    X Trap 2 TS Member

    Joined:
    Jan 29, 1998
    Messages:
    1,125
    I too would suspect the "A" coil as being dirty! Check the top side.

    It can look clean from the bottom side and look like it is covered in tar paper from the top view. Been there and seen it. Cost me an "A" coil once.


    Not an easy job on mine but I do it every so often and run a cable through the drain pipe from the outside in. My unit produces a lot of rust and started in just a few years. I have to vacuum the "A" coil drip pan to get all the rust out and to keep the rust out of the drain. I then clean the "A" coil the at same tine.


    Way off base ...and out in left field...If the fan in belt driven...could condensation from the "A" coil drip pan be dripping on the belt causing it to slip? Ray
     
  14. Primedust

    Primedust TS Member

    Joined:
    Jun 7, 2006
    Messages:
    472
    Common causes of A/C evap coil freezing are:
    Dirty evaporator coil, plugged or partially restricted drain line, Low on refrigerant charge, Poor or lack of air flow, All diffussers not open all the way, dampers closed. Return air grilles dirty or blocked by dressers, beds, clothes baskets etc. Thermostat set below 72 degrees and never satisfies will eventually cause freezing also.

    Also dirty condenser coil, or hail damaged coil with cause the unit to run inefficiently and all the time causing eventual freeze ups. Overhanging tree or shrubs outside also cause inefficient operation. (long run times)

    Freeze ups are usually caused by lack of air movement, not enough diffusers or air flow changes made externally if not by the dirt or filters internally. Also if the system is really old it could be a loose belt, fallen damper (splitter damper) failed zone motor etc.

    The temperature difference across the evaporator coil from inlet to outlet should be close to 20 degrees. If it is higher differntial (more than 20 degrees) such as 29 degrees you have an air flow problem. Much lower than 20 say 12 degrees you have a system problem such as a refrigerant restriction, inefficient compressor, low on charge etc. Hope this helps

    Mark Stevens
    Buffalo MN.
     
  15. Catpower

    Catpower Molon Labe TS Supporters

    Joined:
    Jan 29, 1998
    Messages:
    10,253
    Location:
    In the Cabana
    Cmptrwhiz, sorry if I stepped on your toes, I guess I was a little rude, but I have been doing HVAC/R for almost 40 yrs, and I knew which coil was frozen up, so I apologize

    The cure has been stated quite a few times and if it keeps happening he needs to find someone who can repair it, and no he doesn't need to buy a new system. It more than likely is just a dirty evap coil if it is an upflow they can be a bit#$ to clean if he can get the sheet metal off the end of it you can go in there with a steel brush and gently clean the surface it usually looks like a carpet if you have pets in the house, as their hair will go through even so called high efficiency filters.

    But if the pressures are good then it has to be an air flow problem because in the evening when the ambient temperature falls the head pressure will also fall, and if it is a fixed metering device, ie: acurator or cap tube the suction pressure will also fall, when the saturated suction temperature falls below 32F it will start to freeze up falls

    And it has absolutely no connection with a dirty drain line that comes under "I have a flood in my house heading"
     
  16. JBAGG0705

    JBAGG0705 TS Member

    Joined:
    Aug 11, 2012
    Messages:
    2
    FIRST OF ALL,A PLUGGED DRAIN,WILL NEVER MAKE AN AC UNIT FREEZE.YOU EITHER HAVE A DIRTY EVAPORATOR COIL AND POSSIBLY A LOW CHARGE,BUT YOU WONT KNOW THAT UNTILL BOTH COILS ARE CLEAN.THE REASON IT DOESNT FREEZE UP DURING THE DAY,EVEN IF IT HAD A LOW CHARGE,THE PRESSSURES AND TEMP INSIDE THE SYSTEM REMAIN HIGHER BECAUSE OF THE HEAT LOAD DURING THE DAY.IN THE EVENING.THE HEAT LOAD REDUCES,AND WHEN THE HEAT LOAD REDUCES THE PRESSURES INSIDE THE SYSTEM START TO LOWER.WHEN THE PRESSURES IS REDUCED,SO DOES THE TEMPERATURE.DURING THE DAY,THE HEAT LOAD DOES NOT ALLOW THE TEMPS AND PRESSURES IN THE SYSTEMS TO DROP TO A CRITICAL POINT.MY DEGREE IS IN THIS FIELD,AND I HAVE BEEN DOING THIS MANY YEARS AS WELL.GOOD LUCK.IF SOMEONE TRYS TO COME RECHARGE YOUR UNIT WOTHOUT FIRST CHECKING THE COILS TO BE CLEAN,RUN THEM OFF,THEIR TRYING TO MAKE A QUICK BUCK,BESIDES IT MAY BRING THE PRESSURES UP,BUT THAT COULD ADVERSELT AFFECT THE HEAT LOAD ON YOUR COMPRESSOR AND ALSO REDUCE THE EFFICIENCY OF YOUR UNIT.
     
  17. John Galt

    John Galt TS Member

    Joined:
    Jun 12, 2011
    Messages:
    2,788
    THANKS FOR SHOUTING !!!!!!!
     
  18. mixer

    mixer Well-Known Member

    Joined:
    Jan 29, 1998
    Messages:
    3,386
    Location:
    Coral Springs, Florida
    Most of the reasons & suggestions are too technical for me but assuming all of them are part of the answer there's still one thing that has not been addressed. The freeze up only happens once every 7 or 8 days not every day. I live in S. Florida and the temp & humidity is fairly constant. The a/c system is 7 years old.

    Eric
     
  19. Catpower

    Catpower Molon Labe TS Supporters

    Joined:
    Jan 29, 1998
    Messages:
    10,253
    Location:
    In the Cabana
    Eric the reason it just happens every once in a while is because the temperature of the indoor coil is right at freezing or even a little below freezing when the unit shuts off it warms up and defrosts, but if the temperature load in the house is a little high for some reason the unit will keep running and freeze more then, it doesn't have enough time to defrost between cycles so the next time it comes on it freezes more of the coil, and that continues until the whole coil is frozen up

    Lack of air flow causes 95% of freeze ups, lack of refrigerant can add to the problem but if there is enough air flow it generally isn't

    If your unit is using R22 if the suction pressure gets to 58 PSI it's right at freezing, and that is when the process begins, if you have enough air flow, approx 400 cubic feet per minute per ton the coil won't freeze, if the air flow is less than that it will begin to freeze
     
  20. mixer

    mixer Well-Known Member

    Joined:
    Jan 29, 1998
    Messages:
    3,386
    Location:
    Coral Springs, Florida
    Catpower,

    Thank you for an explantion that makes logical sense I think. The in house air handler unit is in a dedicated a/c closet with a slatted door so I would guessit was designed for proper airflow.. The filter is new and clean. I think having the inside coil removed and professionally cleaned will be the next step.

    Still in all it's the time (7-8 days between freeze ups) that I don't really understand as the temp range in the house is always pretty much the same, 78f daytime & 73f nightime.

    Eric
     
Thread Status:
Not open for further replies.