Heat Pump gets confused


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Old 10-28-07, 07:57 PM
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Heat Pump gets confused

I'm using a Rheem 3Ton heat pump that is about 5 years old with a Hunter Programmable Thermostat. My problem is that it seems like either my Heat Pump or the thermostat gets confused when in heating mode. There are times when my thermostat will kick on the heat pump, the outside fan is operating, and the air coming out of the vents is not warm. It seems like it is just recirculating the room temperature air. I have checked the air at the vents with a temp probe and it is the same temp as the rest of the room. Shutting my thermostat to off and then back on will not solve the problem either. I need to shut off the breakers that control my air handler and outside unit for a few minutes then turn them back on. At this point the heat pump will turn on again and I will get warm air out of the vents. The heat pump might run fine for an hour or a few days, then it goes back to the same situation. If this happens during the night the temperature in my house will drop until the Aux heat kicks on and brings it back up to the set temp.

Anybody have any ideas? When the heat pump operates the way it seems like it should it works GREAT. It's just frustrating to have it get confused and use Aux heat excessively because I know it's just jacking up my electric bill.
 
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Old 10-28-07, 08:37 PM
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When you call for heat, you don't hear the compressor at all, just the fan only outside?

Your out door unit maybe locking out on something, and when you shut down the power, you are resetting whatever may be locking out.

What is your back up heat? (I'm guessing electric since you said you don't want your electric bill to go high)
 
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Old 10-28-07, 09:14 PM
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My back-up heat is the electric strips (Aux Heat) in the air handler.

I'll have to check the outside unit to see if the compressor is running when it is in this condition. This happened a couple of times last winter and I know that at that point the compressor WAS kicking on, I just wasn't getting any heat out of the vents. I could hear the outside fan kick on and run and I could also hear the initial noise/whine as the compressor would kick on.

Is it any indication of the quality of the system that during the summer we had all of the cold air we could possibly want?
 
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Old 10-29-07, 04:22 AM
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Since my wife wasn't available to switch the heat on and off at the thermostat so I could stand by the outside unit to see if the compressor was starting I performed a little experiment this morning.

With an outside temperature of 34F I had the heat on and the vent temperature was around 55F in the house with an ambient temp of about 72F. I switched the thermostat over to AC and got a vent temp of around 55F again. Check my logic here, but I'm guessing my compressor is not kicking on. I tried this experiment to rule out the idea that my reversing valve was not kicking over when the tstat called for heat.

I went outside and tried pressing the reset button on the compressor and that did nothing for me. It did not feel as though the reset had been tripped by the compressor. Any ideas on what to do next (aside from calling a professional)? Is there an simple way to check that the compressor contactor is working? Anything else I should try before calling the pros?
 
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Old 11-01-07, 07:55 PM
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The 55f vent reading with inside temp at 72f would indicate that the unit is operating in defrost mode (AC) Defrost mode can last for several minutes according to how your particular unit controls its defrost cycle. How long are we talking about that your unit stays in this mode approx?? What are your outside temps when this is occurring?? Most of the later model Rheem heat pumps utilize a temp sensor on the coil to detect when the defrost is complete so the cycle is minimized to exactly what is needed. Now if your coil temp sensor malfunctions the board will default into a timed defrost sequence and may be defrosting for way to long. That is one possibility. First you need to verify that the compressor is indeed running when the cold vent temps occur, if it is then we can be pretty sure that the unit is in defrost mode, lets get some timing written down and the outside ambient temps when this is occurring.
 
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Old 11-01-07, 08:47 PM
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Wink

Is this the first year for that tstat ????? Or did it work last winter??????
 
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Old 11-02-07, 09:02 PM
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Sorry I haven't responded promptly. PROBLEM SOLVED. My thermostat has gone bad. It has not been energizing the reversing valve properly. My Rheem heat pump (and possibly all Rheem heat pumps) has a reversing valve that gets energized when the thermostat calls for heat. I took a couple of pieces of wire to manually engage the air handler and the heat pump @ the thermostat (after turning the tstat off). When I jumpered the correct wires to turn on the air handler and the heat pump in heating mode everything worked great. I was getting very warm air out of the vents. I took the programmable tstat off and put the old, plain, digital Honeywell tstat on. Things have been working perfectly ever since. After talking with a couple of HVAC guys I learned that they are not big fans of Hunter tstats and they definately do not recommend Hunter tstats used with Rheem heat pumps. Apparently, most other companies use reversing valves that are energized in cooling mode. Even though there is a switch on the Hunter thermostat to account for the different reversing valves the Hunter tstats apparently get confused and then stop working correctly altogether.
 
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Old 11-02-07, 09:07 PM
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Glad to hear you got it figured out.

Yeah, I agree about the Hunter's stat. If you want a good stat, look into the Honeywell VisionPro t-stat.
 
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Old 11-06-07, 09:50 AM
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Wink

The thinking behind the 4 way valve in all the other unit is. That you can live with out the AC but not with out heat. So if the valve goes out and cant work . The unit can give you heat.
 
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Old 11-15-07, 06:56 PM
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Obviously Rheem just wanted to be COOL (pun intended) Hunter t-stats are a pretty poor excuse for a t-stat, the Honeywell Vision Pros are very impressive. I have to get me one of those one day when I get rich.
 
 

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