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  1. #1
    Join Date
    Feb 2006
    Posts
    103
    I recently had a new Amana, dual fuel, 2 stage heat pump installed. I also had a new variable speed, high efficiency, 2 stage gas backup furnace installed. The system is hooked up to a honeywell vision pro stat. After the installation I had some issues with the ductwork so the installer sent out a tech. The tech corrected the ductwork but said the system wasn't programmed correctly. He said the heat pump and furnace were turning on at the same time. Obviously this shouldn't happen. According to my wife he spend between about 2 hrs correcting the problems, but he said he has it fixed. This is the first time I've owned a heat pump. Here are my questions:

    1. Has the simultaneous operation of the furnace and heat pump damaged the system?

    2. Now I notice that the blower sometimes kicks on and blows out what feels like cool air. When I look out the window at the compressor I notice it's not on. When the compressor turns on in a minute or two the air heats up (although not as much as when the furnace is on). Is this correct system operation, or should there be no air flow until the compressor is on?

    3. I definitely notice that the furnace blower is sometimes blowing softly and other times it ramps up to full speed. What controls the system's fan speed decision?

  2. #2
    Join Date
    Dec 2005
    Posts
    783
    Model and name of the unit?

  3. #3
    Join Date
    Apr 2004
    Posts
    7,680
    1. No, not if it still runs.

    2. Probably a time delay in the outdoor unit. The thermostat already has one so the OD one can be eliminated.

    3. Fan only position may run fan at 50% of full cooling (heat pump) speed. Also there may be some ramping profiles in the ECM module.

  4. #4
    Join Date
    Feb 2006
    Posts
    103
    Heat Pump is an Amana Ultron 16 SEER, RTG48C2C and the furnace is an Amana 96% AFUE, AMV90905DXA.

  5. #5
    Join Date
    Dec 2005
    Posts
    783
    Listen to what he said


    1. No, not if it still runs.

    2. Probably a time delay in the outdoor unit. The thermostat already has one so the OD one can be eliminated.

    3. Fan only position may run fan at 50% of full cooling (heat pump) speed. Also there may be some ramping profiles in the ECM module.

  6. #6
    Join Date
    Feb 2006
    Posts
    103
    I appreciate the help, but I'm not sure I understand the second point about the outside unit delay. I think what you are trying to tell me is that the stat turns on the blower because it thinks the heat pump is on, but the heat pump is not on because it is in a delay mode created by the outside unit. Am I understanding this correctly? If so, is it easier to turn off the stat delay instead of the outside unit delay? In either event I will have the contractor do it. Although I'm a DIYer I would never attempt to fix my HVAC unit. I'll stick to paint, trim work and other handyman tasks.

    As for the ECM module. I would be interested to know its ramp up settings. I don't see them in the owner's manual. How does one obtain them?

    Thanks for the help.

  7. #7
    Join Date
    Dec 2005
    Posts
    783
    Since you just had this installed it would be best for you to go back to your contractor. I do not suggest playing with your new unit or you may cause damage and void the warrenty. If you really want to learn about this business find a good course and take it. There are to many variables in what you are doing.

  8. #8
    Join Date
    Feb 2006
    Posts
    103
    hvac1000, I agree with you and have no intention to work on the HVAC system. I have enough things on the "honey do list". I'm just trying to understand the issues and potential solutions so I can speak somewhat intelligently to the contractor.

  9. #9
    Join Date
    Feb 2006
    Posts
    103

    Calling RoBoTeq

    RoBoTeq given your knowledge of the Amana/Goodman equipment maybe you have some thoughts on my questions?

  10. #10
    Join Date
    Feb 2006
    Posts
    103

    refresh

    refresh

  11. #11
    Join Date
    Mar 2004
    Posts
    1,042
    This heat pump will have a high pressure switch, so a little simultaneous operation shouldn't have done any serious damage.

    Are you familiar with the heat pump defrost cycle? That could explain some of what you're describing. The outdoor fan will stop while it is defrosting, and the compressor will keep running, but temporarily in cooling mode. The indoor blower will run during that time. Depending on the setup, the ductwork could be blowing cold air (from being in cooling mode), or it may run the furnace during the defrost cycle to avoid blowing cold air. That's the only time it's ok for the furnace and the compressor to run simultanously, when defrosting. The effect and purpose of all of this is to get the coils of the outdoor unit hot enough to remove all of the frost that can accumulate on them during heat pump heating.

    If it didn't defrost, eventually the coils would be completely plugged up with frost and ice, and the system's output would drop off to near zero. The defrost cycle isn't ideal for efficiency, but it's a necessary part of heat pump heating in cold weather. On this unit, the duration and frequency of the defrost cycles depends on weather conditions. In general, the colder and wetter it gets, the more frequently defrosting will be needed. As a ball park, a typical defrost cycle takes 5-10 minutes and will take place every 60-180 minutes of run time. Typically at the end of each defrost cycle you'll see some steam rising from the outdoor unit.

    The thermostat and the outdoor unit probably both have a 4-5 minute delay to prevent starting the compressor within 4-5 minutes of when it last shut off. If the timing is a bit different, or if the installer disabled the thermostat's timer because the outdoor unit already has its own timer, you may get the thermostat calling for heat and the blower starting before the outdoor unit is ready to start again. That would only be the case when it had just cycled off in the last few minutes, though, so I would lean more towards defrosting as explaining what you're seeing.

    I'll add to the earlier comments on why the fan speeds may be different under different conditions. You have a two speed heat pump; depending on whether it's running on low or high, the indoor blower speed has to change to suit that. Depending on the conditions, it may start up directly in high speed (to recover from a thermostat setback period); that would cause the blower speed start out much higher than it would if it were starting up in low speed in conditions where there's less demand for heat. Also, the fan speed for furnace heating may also be different than what the system uses for heat pump heating.

  12. #12
    Join Date
    Feb 2006
    Posts
    103
    wyounger, thank you for the explanations. I think hvac manufacturers should hire you to write explanations about their equipment. You make more sense than the current owners manuals. If I understand you correctly I think I should be telling my contractor that the unit blows cold air from time to time when the outdoor unit fan is off. A likely solution is either the stat has to delay calling for air during the defrost mode (or while the outside unit is in delay mode) or the furnace needs to be programmed to kick on during this short period. I wonder if that was the way it was originally programmed when the tech thought both were operating simultaneously. I also wonder if they've ever installed this particular combination of equipment, or if I'm the guinea pig. On the positive side, to date they have been professional and responsive to my inquiries and concerns. Also the equipment is so much quieter than my old system, althought the sound of the variable air flow is noticable.

  13. #13
    Join Date
    Feb 2006
    Posts
    103
    Okay, just spoke to the service tech who was back out to the house to level the outside unit (that's a different story). According to the service tech what I'm describing is normal operation for a heat pump. The stat says turn on the heat, but the outdoor unit may happen to be in either delay or defrost mode. The furnace blower turns on but the heat pump is not sending heat. What you feel from the vents is recirculated air. It isn't cooled air but it feels cool to the skin because it's moving across your skin. It would be nice if the furnace blower would turn off during the delay and defrost mode but there isn't enough communication between and among the furnace, stat and heat pump to allow for such an operation. Moreover, I'm told not even the Carrier/Infinity series has that level of communication. In theory if the defrost/delay modes continued for long enough to drop the stat a few degrees, then the furnace would fire up, but this isn't likely to happen under most circumstances.

    wyounger (and others familar with heat pumps), is this explanation consistent with your understanding?

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