Control Board Question

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Beekster

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Aug 9, 2011, 8:07:48 PM8/9/11
to Hallowell Acadia
Can anyone answer this question:

"It would be good to find out how the deice cycle works. I would
guess that they just monitor the coil temperature for temperatures
lower than freezing, maybe when the air temp is low too. Then they
reverse the cycle for a short time to heat and defrost the coils. The
question I have is whether the strategy is variable, do they heat
longer or more frequently if the air temperature is lower, if the
booster compressor is on, etc.?"

Any insight is welcome.

dod

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Aug 22, 2011, 10:21:32 AM8/22/11
to Hallowell Acadia
For All Climate Heat Pumps and Acadia CH&C Systems using the older
control it's essentially the same defrost mechanisms as most other
premium units on the market. There's 3 methods they enter defrost
(active, passive, and forcibly), and 2 methods they exit (active and
passive):

For entering:

The active system monitors outdoor temperature and the suction
temperature on one of the distributors of the coil on the outdoor
unit. There's a control algorithm that looks for a temperature
spread between the two at temperatures where condensate can freeze on
the coil. When the algorithm is satisfied (i.e. it is determined that
the likelihood of formed ice is very high) the unit will defrost.

The passive system uses timers built in to the control that will force
defrosts in certain operating modes after operation in that mode has
accumulated a set number of minutes below certain temperatures should
the algorithm not be keeping up.

The forced method (on the original - non-invensys controls) there is a
manual defrost jumper that will force a defrost every 45 minutes.

The defrost termination is determined by the temperature at the
distributor coil reaching a specified value for all defrosts for
active, or a maximum number of minutes being reached for passive.
Upon completion of a defrost the unit will go through the appropriate
sequence to continue operation in its last known operating mode,
assuming the thermostat is still not satisfied.

If the unit does not complete a successful defrost automatically
within the defrost time limit, it will attempt again in 45 minutes.

On the whole the defrost strategy is focused on keeping the coil clear
enough for safe, effective operation. It works independently of
thermostat calls and operating modes.

Hope this helps!

Chris Papademetrious

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Aug 23, 2011, 6:33:51 AM8/23/11
to hallowel...@googlegroups.com
This is terrific information! It would be great if you could post
this to the savemyacadia forum.

- Chris

Chris

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Aug 28, 2011, 10:42:33 PM8/28/11
to Hallowell Acadia
Thanks Dod, I have a question:
Could you detail the sequence of the operation of the reverse valve
and compressor stop and start when entering and leaving defrost. Say
the outdoor temp is 13 degrees F and the primary compressor is running
2cyl and the booster is on. Do both compressors shut down before the
reverse valve is actuated? Is there a 2 minute delay after shutdown
before restarting or does the primary continue to run in 2 cyl when
entering defrost? Does defrost run 1 cyl or 2 cyl? Is this sequence
the same when ending defrost? Thanks again!!

MICHAEL BARRICK

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Aug 29, 2011, 8:19:44 PM8/29/11
to hallowel...@googlegroups.com
the booster drops out for defrost then there is a delay, defrost only energizes when high stage is enabled or temp or time it will not energize when on low stage at all
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