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Old 03-20-2011, 01:21 PM   #1
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Frigidaire heat pump thermostat options


My buddy has a Frigidaire electric furnace and heat pump.

Furnace:
B3BM036K-B
Heat Pump:
FT3BA-036KA

He had a Robertshaw 9620 110-732C

He got a Honelywell RTH 111 and it says right on it that it doesn't support heat pumps with backup heat.. He has heatstrips in his furnace..

The new thermostat doesn't have a connection for the blue common wire and so when he trys to use the heatpump, it never turns off.. The temp just keeps climbing..

1. What would be a better thermostat for this setup?
2. Is there an switch over thermostat in the outdoor unit for backup heat? I didn't see a separate control board in the heat pump. Just the main control circuit board, and the wiring diagram on the inside of the panel says the external thermostat is optional..
3. How do you set the cut-over point or disable it if you were going to hook up a vision pro 8000 with outdoor thermostat wire connected to the indoor thermostat unit.

Is the VisionPro 8000 overkill for this?

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Old 03-20-2011, 06:53 PM   #2
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Frigidaire heat pump thermostat options


Quote:
Originally Posted by zootjeff View Post
My buddy has a Frigidaire electric furnace and heat pump.

Furnace:
B3BM036K-B
Heat Pump:
FT3BA-036KA

He had a Robertshaw 9620 110-732C

He got a Honelywell RTH 111 and it says right on it that it doesn't support heat pumps with backup heat.. He has heatstrips in his furnace..

The new thermostat doesn't have a connection for the blue common wire and so when he trys to use the heatpump, it never turns off.. The temp just keeps climbing..

1. What would be a better thermostat for this setup?
2. Is there an switch over thermostat in the outdoor unit for backup heat? I didn't see a separate control board in the heat pump. Just the main control circuit board, and the wiring diagram on the inside of the panel says the external thermostat is optional..
3. How do you set the cut-over point or disable it if you were going to hook up a vision pro 8000 with outdoor thermostat wire connected to the indoor thermostat unit.

Is the VisionPro 8000 overkill for this?
1.) RTH7600D is a good choice. 2.) The stat will pull on aux heat as needed. 3.) Follow the instructions in the manual, as you will have to set up a number of parameters at the time of installation anyway.

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Old 03-20-2011, 10:27 PM   #3
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Frigidaire heat pump thermostat options


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Originally Posted by hvactech126 View Post
1.) RTH7600D is a good choice. 2.) The stat will pull on aux heat as needed. 3.) Follow the instructions in the manual, as you will have to set up a number of parameters at the time of installation anyway.
I didn't think that the old stat had an external thermostat. How can I tell if the outdoor condenser unit has a built in tstat?
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Old 03-21-2011, 06:30 AM   #4
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Frigidaire heat pump thermostat options


itdoesn't have an external most likely, it will bring on aux automatically by droop. ( difference in set temp and actual temp in home)
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Old 03-23-2011, 05:49 PM   #5
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Frigidaire heat pump thermostat options


So do you know how it knows to use the backup heat or not? If it is not getting there very fast, does it then use the backup heat after so much time, or if it has 4 degrees to travel it uses the backup heat?

Seems like there are two modes you'd want to use for a heat pump:


A. It only has to go up 1 degree but it is really cold outside so backup heat is required. If it doesn't know the temp, it seems like it would try, then not get very far and then backup heat would kick in..

B. Or it has to go up 5 degrees and so it will use backup heat so that it doesn't take forever.. Does it just jump straight to backup heat?

Without knowing what temperature it is outside, how does this thermostat do it?


I'm also thinking about getting a vision pro 8000. It has the ability for an external temp sensor, but will it also work on a heatpump without it just like the 7600?

-Jeff
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Old 03-23-2011, 09:43 PM   #6
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Frigidaire heat pump thermostat options


8000 uses Interstage Differential: operates with droopless control. Once the thermostat senses that 1st stage is running
at 90% capacity, the thermostat energizes 2nd stage.

unsure on the 7600, but I believe it is the same way.

basically it uses its microprocessor and takes multiple readings and uses an algorithm to figure out when to stage in the Aux heat.

P+I Control
The thermostat microprocessor-based control requires that
the user understands temperature control and thermostat
performance. A conventional mechanical or electronic
thermostat does not control temperature precisely at setpoint.
Typically there is an offset (droop) in the control point as the
system load changes. This is a phenomenon that most people
in the industry know and accept. Many factors contribute to
offset including switch differential, thermal lag, overshoot,
cycle rates and system load.
The thermostat microprocessor simultaneously gathers,
compares and computes data. Using this data, it controls a
wide variety of functions. The special proprietary algorithm
(program) in the thermostat eliminates the factors causing
offset. This makes temperature control more accurate than
the conventional mechanical or electronic thermostats. The
temperature control algorithm is called proportional plus
integral (P+I) control.
The thermostat sensor, located on the thermostat or remote,
senses the current space temperature. The proportional error
is calculated by comparing the sensed temperature to the
programmed setpoint. The deviation from the setpoint is the
proportional error.
The thermostat also determines integral error, which is a
deviation based on the length of error time. The sum of the
two errors is the (P+I) error. The cycle rate used to reach and
maintain the setpoint temperature is computed using the P+I.
The addition of the integral error is what differentiates the
thermostat from many other electronic and mechanical
thermostats.
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Last edited by hvactech126; 03-23-2011 at 09:46 PM.
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Old 03-24-2011, 04:26 AM   #7
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Frigidaire heat pump thermostat options


The 8000 series is an indoor temp based control for aux heat, unless an outdoor sensor is used. Then it is indoor and outdoor temp based.

The IAQ thermostat is a much better thermostat to use.

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