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CAPThomas
3 Posts |
 Posted - 01/10/2010 : 10:39:40 AM
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I have a two year old Harmony III 4 zone system with a G60UHV gas furnace. We're in Central Florida and have just this week experienced a prolonged period of cold weather. The system is marginally able to support heat demand and, with constant thermostat demand, keeps cycling the burner on for about 3 1/2 minutes and then off for five minutes. The fan runs constantly, but at a low speed.
Question - when properly wired, does the Harmony III completely override the heating blower speed and blower speed adjustment dip switch settings on the G60 control board, or are those settings still available to increase the base blower speed / air movement?
I've got a service call scheduled in two days, but my experience has been that the technicians have very little knowledge of zoning and gas furnaces with variable speeds. They are used to heat pumps and E-Heat technology, because not many sub-divisions in this area have natural gas available.
Cap
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slctech
1098 Posts |
Posted - 01/10/2010 : 1:35:35 PM
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The Harmony III utilizes the blower performance settings on the furnace as a base reference to operate the blower motor with in those perimeters.
The furnace board settings are not just a guessing game or an install and assume factory default is the best bet. We run the furnace blower in COOL mode with all the dampers open and independent of the Harmony III control. We take static measurements and correlate these measurements with the engineering specs to properly determine our CFM settings. Once these settings are locked in, I would for example have a base CFM minimum rate of 850cfm and a maximum cfm of 1400 cfm. In essence we want the base board settings to determine the maximum cfm when all four zones are calling and match that maximum cfm with what the duct work can appropriately handle.
The Harmony III is then set up through separate measurements and sizing of each of the zones, this is broken down by percentages on the PIAB zone pins on the Harmony III. So if only one zone is calling the board will ramp up or ramp down the motor somewhere between the minimum and maximum cfm settings of the board.
So back to the example before listed. We know the minimum available cfm the board will allow is 850cfm and the maximum is 1400cfm. All combinations of zones calling or not calling for Heating or Cooling will fall somewhere within the set minimum and maximum board settings.
The discharge sensor located in the plenum monitors the air temperature and makes sure that on lower cfm settings the furnace is not over-heating or the A/C is not freezing up and will cycle the equipment appropriately. It is a fine line between all the CFM settings on the furnace blower board and Harmony board to minimize the amount of controlled cycling of equipment when it comes to the discharge sensor. Cycling is going to happen even on a perfect system, it is the art of tweaking the system to bring it down to a minimum.
I see a lot of single stage air-conditioners installed on Harmony III's and it makes me cringe..they'll get the crap kicked out of them due to all the cycling.
If it all sounds to confusing..I'm sorry. There really isn't a good way to put this all into layman terms for me. Here is the Harmony III manual..see pages 10-13
http://tech.lennoxintl.com/PDFs/505023r.pdf
Here is the engineering manual for your furnace, see pages 12-22 for blower performance settings.
http://tech.lennoxintl.com/PDFs/ehb_g60uhv_0812.pdf
As a Lennox Technician I feel basic repairs and maintenance can be performed by the homeowner. But I highly suggest that periodic maintenance should be made by a certified licensed technician. You should contact your local Lennox technician for any repairs or issues that are outside your comfort zone. Property damage, personal injury, and death can occur from improperly repaired or maintained systems. Replacing a part doesn't always resolve the issue that caused the part to fail! |
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CAPThomas
3 Posts |
Posted - 01/11/2010 : 09:16:44 AM
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Thanks very much for the detailed reply. For board readers, I'll try to report back after the HVAC service call to tell you what they decided was needed to fix / change.
Cap |
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CAPThomas
3 Posts |
Posted - 01/11/2010 : 6:11:18 PM
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Service Technician checked the discharge air sensor, all dampers, Harmony III, and furnace today. He decided that a new blower / control was needed and it has been ordered. We'll see if that fixes the problem. I'm a bit dubious as the blower was able to ramp up / down for cooling mode, but won't do it for heating mode.
Cap |
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