DIY Home Improvement, Remodeling & Repair Forum > Appliances > HVAC > Heat pump not hitting target temp




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Old 07-13-2008, 02:54 PM  
pens66
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Default Heat pump not hitting target temp

Hi,

I have a heat pump and had many problems with the original install. The service techs were back every time I switched between heating and cooling to tweak the system to get it to work. Each time they made adjustments, it did work and would cool to the desired temperature.

This cooling season, when the cooling was once again not working (the coils/pipes would completely freeze up and the cool air would stop) I got fedup and called another service company.

The new company raised the coil within the furnace (the heat pump is an add on to an oil furnace) and increased the blower motor size to increase the overall air flow. They also replaced a sensor that I guess tells the system when the coil is about to freeze up and thaws it out before freezing.

The frozen coil issue has been fixed, the problem now is the AC never hits the desired temperatures. The latest company says that is normal and heat pumps are designed to do the best they can, but it is not uncommon for them to not hit the target temperature. I don't live in an extremenly hot climate, dor example mid 30's is considered a really hot day, with most hot days being between 28 and 32 outside. When the temperature is that outside, if I set the inside thermostat for 18, the system will only cool to 20ish. It actually does not cool, but rather hold an existing temperature - what I need to do is leave the heat pump running all night set at 18, then when I wake up it will be around that temperature and I'll leave it running all day and the temperature inside will slowly rise up to 20 - 21, but will not hold at 18. Furthermore, there are times when it is actually cooler outside than inside (it'll be 20 outside, I'lll have the heat pump set at 18 inside and it will only cool to 21). This does not seem normal to me. Does anyone have any suggestions as to how to increase the cool air being produced by the system?

Just FYI - the techs spent several days coming back and changing the coolant, adjusting this and that - I ended up spending approxmitaly 1/3rd the cost of a new heat pump to date with the recent round of servicing.

Thanks,



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Old 07-13-2008, 04:12 PM  
geo
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my first thought is your fan should have ben upsized to acomodate the ac
. did you have ac before? do they have a duel feul control? if you had an ac before was it the same size.



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Old 07-13-2008, 05:20 PM  
glennjanie
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Hello Pens:
Some critical points for heat pumps;
1. Good strong air flow. Your floor registers should blow the curtains.
2. Well balanced refrigerant (high side and low side)
3. A properly sized metering device.
4. Clean coils both outside and inside.
5. Make sure the unit is disposing of the humidity (collecting and draining).

If your house is well insulated, a properly sized system should be able to cool the house within an hour after you come home from work. A programable thermostat would start it an hour before you come home and it should be as cool as you left it in the morning. BTW programables will save you 30% on your energy bill.
Glenn

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Old 07-14-2008, 05:55 PM  
geo
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Default All due respect

everything you said was the truth with the one exception of programble t-stats saveing any money on 2 stage equipment especialy heat pumps. I sure its a standard thing you post for most questions but I will explain for everyone else. If you are maintaining a temp 9 times out of 10 the 2 stage whether that be an electric resistance heater or an oil furnace wont turn on . if the temp is adjusted frequently by a set-back t-stat or manuel the second stage will kick on ( usualy set for a 4 degree difference between the set point and the room temp.) sometimes you will lose money other's break even others you will save . but not worth it . ironicly almost all heatpump thermostats are set-back so it doesnt realy matter

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Old 07-16-2008, 10:13 PM  
pens66
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Hi,

For #5 below - stupid question, but if the system is not disposing the humidity correctly, will this casue the entire system to not work properly?

As you probably guessed, I know very little about heat pumps - but I was just outside looking at the exterior unit and the humidity disposal cord is a plastic clear tube that runs from the inside and is laying on the rocks on the outside. The heat pump has been running all day today, so I was surprised when I looked at the tube and it was dry and the rocks around were also dry - I am assuming there should be some evidence of water somewhere. I then looked at the inside unit and the clear tube coming from the furnace setup that goes into a lower pump was also dry - so it would appear that this is not functioning correctly.

Should these tubs have a slow steady stream of water flowing through them when the cooling is on?


Quote:
Originally Posted by glennjanie View Post
Hello Pens:
Some critical points for heat pumps;
1. Good strong air flow. Your floor registers should blow the curtains.
2. Well balanced refrigerant (high side and low side)
3. A properly sized metering device.
4. Clean coils both outside and inside.
5. Make sure the unit is disposing of the humidity (collecting and draining).

If your house is well insulated, a properly sized system should be able to cool the house within an hour after you come home from work. A programable thermostat would start it an hour before you come home and it should be as cool as you left it in the morning. BTW programables will save you 30% on your energy bill.
Glenn
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Old 07-17-2008, 11:29 AM  
glennjanie
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Hello Pens:
The condensate drain line should include a trap at the outside end to keep bugs from going in there for the water. They die there and get all wadded up, thus stopping the flow of condensate.
I would take the tube off at the indoor coil and blow it out, make sure the indoor coil is creating condensate, and reconnect the tube with a running trap at the end.
If the unit is not extracting humidity from the air, it has to get very cold to do any good. The low humidity causes the persperation on your skin to dry quickly, making you feel cool. Here in the Southland we can step out the door for a quick demonstration. Our humidity is normally very high and it is stifeling.
Glenn



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