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Old 01-19-2010, 06:27 PM   #16
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O/D temp that triggers defrost


Yep.

Just a 6 hour safety defrost.

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Old 01-20-2010, 09:26 AM   #17
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O/D temp that triggers defrost


Been There,

Once again, you helped me with my questions. Thank you for your assistance.
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Old 02-19-2010, 08:09 AM   #18
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O/D temp that triggers defrost


Follow up question relatinf to the demand defrost function.

Under the "Calibration Mode Sequence" literature in the manual, it states: DEMAND Mode= Accumulate compressor runtime of more than 30 minutes while coil temp is below 35 deg. When the auccumulated compressor time exceeds 6 hours or if the coil sensor indicates frost is present on coil, go to defrost.

Does this mean that the defrost board will check for frost every 30 minutes or is it a constant monitoring scenario? In other words, will it on go into defrost at 30 minute increments if needed, such as 30, 60, 90, 120, 150, etc. minutes?
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Old 02-19-2010, 03:04 PM   #19
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O/D temp that triggers defrost


The coil sensor has to also indicate frost is on the coil, in order for it to go into defrost. With the exception of the 6 hour forced defrost to ensure the outdoor coil isn't oil logged.

As long as the coil temp is under 35, it is timing the compressor run time. And the timer does not reset until either it goes into a defrost, the coil temp rises above 35, or the board's 24 volts is de-energized.

So after a defrost, it can't go into a defrost again for 30 minutes.

Demand defrost monitors the difference between coil and air temp to determine if a defrost is needed.

It would be possible during heavy snow, sleet, or freezing rain to have it go into defrost evey 30 minutes.

But not during any normal operation conditions.
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Old 02-19-2010, 06:35 PM   #20
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O/D temp that triggers defrost


I am in SC so the chance of heavy yet any snow is virtually nil, except for last weekend which is anothe story.

I need you assistane, Been There as I can't seem to get a straight answer from various sources.


How can the sensors know there is frost present just by looking at the coil and air temp? There have been many times that my unit goes into defrost even though there is no visible frost present.

My problem since the unit was installed is that no matter what the outdoor conditions are, the unit has reverted to an uncalibrated time/temp defrost which will occur every 45 minutes. The sensors and board have been replaced numerous times including just two days ago with the guidance of Lennox themselves.

Now, mind you where I live the unit only goes into defrost mode when it gets cold during the night, whereas it is difficult to monitor without staying awake all night.

Like I stated, a new harness and board were installed two days ago. This morning, since I happend to be lying awake listening to the stupid thing, I timed that a defrost occured about 60 minutes after the previous one, and the next one occured about 30 minutes after that.

So now, it appears to me that the default 45 minute time/temp defrost didn't happen.

Based on my quote from the manual in my previous entry to this thread, I am wondering if under Demand mode, the unit checks every 30 minutes for frost , and then initiates one or does it constantly monitor and create a defrost scenario at any time thereafter.

Last edited by jeepgrady; 02-19-2010 at 10:47 PM.
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Old 02-19-2010, 07:47 PM   #21
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O/D temp that triggers defrost


Its a constant monitoring. Once the coils temp reaches 35 for 30 minutes of compressor accumulated run time. It monitors both the air temp and coil temp. Until it does a defrost(or temp goes above 35, or 24 volt power is lost to the board).

It determines if there is frost or ice on the coil by the difference between air temp and coil temp.
If the difference is more then X then the coil is covered by ice or frost in an amount that is prohibiting heat transfer.
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Old 02-19-2010, 07:48 PM   #22
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O/D temp that triggers defrost


Good chance. You are having a mechanical problem.

Like an outdoor TXV that is not always allowing enough refrigerant go through it.

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