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  1. #1
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    Apr 2005
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    Kingston Ontario Canada
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    I thought maybe one of you Carrier guy's would have an opinion of this for me. I have a Carrier 38YZA Heat Pump and FV4A Fan Coil and programmable Thermidistat Control. When the Heat Pump is in cooling mode, and I have the Thermidistat in normal dehumidify operation, or on cool to dehumidify the heat pump seems to short cycle at night when the cooling load is at it's lowest. Is this a indication that the heat pump is too big? If so what could I do about it?

    Thanks, Thorton

  2. #2
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    Aug 2002
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    Office and warehouse in both Crystal River & New Port Richey ,FL
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    10 minutes on ,10 off,is it shorter than 10 minutes?

  3. #3
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    Apr 2005
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    Originally posted by dash
    10 minutes on ,10 off,is it shorter than 10 minutes?
    Hi Dash: thanks for responding. I have did read in my Thermidistat Conrol book that the cool to dehumidify demand that the compressor runs a maximum of 10 minutes on and 10 minutes off. In my application I don't think it does run for 10 and 10, sometimes 7 minutes on and 7 off.
    Do you think that is because the tonnage is too much for my house? When I had this heat pump installed, it replaced an air conditioner that was 2 tons. The Carrier 38yza is 2.5 tons. I have a 1400 sq ft bungalo, with all dark brown brick and brown vinyl windows and south west exposure.Also don't you think that 10 min on and 10 off will take it's toll on the compressor over time?

    Thorton

    [Edited by thorton on 04-25-2005 at 08:55 PM]

  4. #4
    Join Date
    Jul 2002
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    Zelienople, Pa
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    Did you have a load calc done BEFORE purchasing your system?
    How tall are you Private???!!!!

  5. #5
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    Aug 2002
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    If the 2 ton cooled the home well on the hottest days ,2.5 ton is too large.But as stated above ,a load calculation ,will tell for sure.


    The 10 on and 10 off,will cycle off sooner if the temperature at the stat goes 2 or 3 degrees below the set point,if that's the case,oversizing is making it worse.

  6. #6
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    Originally posted by dash
    If the 2 ton cooled the home well on the hottest days ,2.5 ton is too large.But as stated above ,a load calculation ,will tell for sure.


    The 10 on and 10 off,will cycle off sooner if the temperature at the stat goes 2 or 3 degrees below the set point,if that's the case,oversizing is making it worse.
    Hi Dash: Thanks for responding, again. No, the temp doesen't drops any more then 1 degree. When I called the dealer who installed, he in turn called Carrier, and they said to adjust the anticipator(option 1) on the Thermidistat from the factory setting(which is 3) to a higher setting with I set at 9.But still seems to run too short of times. But I will re-evauluate when the warmer weather gets here and I'm using air conditioning mode in the heat pump.

    Thanks again, thorton

  7. #7
    Join Date
    Apr 2005
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    Kingston Ontario Canada
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    Originally posted by Yellow Dot
    Did you have a load calc done BEFORE purchasing your system?
    Hi Yellow Dot: No we didn't do the heat loss and heat gain calculation. I discussed it with the intalling dealer, and he didn't think its was necessary, but would do it if I insisted. The reason I went with the 2.5 tonnage is, it had slightly better HSPF then the 2 ton unit. As far as the cooling end of it, my previous air conditioner was a 2 ton, and it did cool the house fairly well, I always wished it was a little bit bigger. Although, the summers haven't been near as hot and humid as they were ten years ago, so that might be showing up now with they larger 2.5 ton unit. I would also like to add, that HSPF rating on the heat pump was more critical because I was replacing a 20 kw electric furnace with a 15kw two stage FV4A fan coil.

    Thanks, Thorton

  8. #8
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    Jul 2002
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    Load calcs never lie...
    Whats more important? HSPF of the correct size.
    An oversized unit will eat up any savings you would gain from the efficiency...
    Live and learn....
    How tall are you Private???!!!!

  9. #9
    Join Date
    Aug 2002
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    Office and warehouse in both Crystal River & New Port Richey ,FL
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    Calcs don't lie but liars calculate.

    Not anyone here but,there are some variables that will change the result.Like interior window shading or not ,can make a 1/2ton difference on a home.

  10. #10
    Join Date
    Apr 2005
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    Kingston Ontario Canada
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    Originally posted by dash
    Calcs don't lie but liars calculate.

    Not anyone here but,there are some variables that will change the result.Like interior window shading or not ,can make a 1/2ton difference on a home.
    Right on Dash, that's why I said the previous air conditioner did the job fairly well, although I wished it was a 1/2 ton bigger on some days. Back in 1987 when I had this house built the summers were much hotter and more humid so I felt the 2.5 ton heat pump would be ok. However, the last 7 to 8 years, not nearly as hot and humid. The 2.5 ton unit runs long enough during the day when the heat load is much greater then at night. For a while I thought it might be the Thermidistat placement too! It's located in a hall right outside of the bathroom, so I closed off the register in the bathroom. There is a lot of traffic in a hall like this too. It seems everytime somebody would walk down the hall the Thermidstat activates and the heat pump would come on.

    thorton

  11. #11
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    Just to be clear,load calc is the best way to go.Just saying that with two different people,the results may differ.

    When increasing the system size,the duct system often needs to be larger as well,that's a Man.D calculation.What size filter and return grille do you have?

  12. #12
    Join Date
    Apr 2005
    Location
    Kingston Ontario Canada
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    Originally posted by dash
    Just to be clear,load calc is the best way to go.Just saying that with two different people,the results may differ.

    When increasing the system size,the duct system often needs to be larger as well,that's a Man.D calculation.What size filter and return grille do you have?
    Hi Dash: I think I've got it figured out. Maybe the reason the heat pump short cycles in cooling mode is I have a evaporator freeze stat. Maybe what is happening is, rather then the 10 mins maximum on and 10 mins off is being overridden by the evaporator freeze stat shutting down the heat pump until the evaporator is free of frost and then starts back up again. This being said, there is something else that comes to my attention is the fifteen-minute cycle timer that keeps the comressor from running at least 15 mins after the last start of the same cycle it's function is to assure the equipment is not cycles more then 4 times per hour. What do you think?

    Thanks thorton

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