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Old 10-13-2009, 11:20 AM   #1
zep
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Low speed fan heating?


4 ton heatpump with VS airhandler
HEATPUMP - WITH 1 STG EMHT 1 STG AUX HEAT
NOTES:

3.) IF OT2 PJ2 JUMPER IS CUT E AND W2 ENABLE

LO SPD FAN HEATING

New to home and heatpump. I am getting ready to switch over to heating. Being the geek that I am, I have read the operating instructions for the system and have determined that the jumper that allows for low speed heating has not been cut. Is it neccessary to enable low speed heating?

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Old 10-13-2009, 12:36 PM   #2
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Low speed fan heating?


You need to determine how much heat is installed before cutting the jumper.

Most 4 ton heat pumps have 15 KW or more of aux heat.

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Old 10-13-2009, 12:43 PM   #3
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Low speed fan heating?


The heat pump has 10 KW of auxillary heat installed.
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Old 10-13-2009, 12:56 PM   #4
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Low speed fan heating?


The note you posted is for 2 stage.

The note for single stage is to cut OT1 PJ4 jumper.
So cut the OT1 PJ4 jumper.

This will allow full blower speed on an aux heat call. But still use low speed when you switch to emergency heat.
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Old 10-13-2009, 01:31 PM   #5
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Low speed fan heating?


That note about cutting OT1 PJ4 refers to HEATPUMP-2 STGE EMHT 1 STAGE AUX HEAT diagram below on page 4. My heat pump has 1 STG EMHT 1 STG AUX HEAT as outlined above which states that cutting OT2 PJ2 would enable low speed fan heating. What am I missing here since there is only one set of emergency heat strips installed on the heatpump?
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Old 10-13-2009, 04:07 PM   #6
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Low speed fan heating?


Still better to cut the OT1 PJ4 jumper.
With only 10KW of strip, you don't want high speed when E(emergency heat) is on. Or you will only get a 20F temp rise when in emergency heat.
The air would be much cooler coming out of the registers at the supplies at the far end of the duct system.
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Old 10-13-2009, 04:27 PM   #7
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Low speed fan heating?


Would cutting OT1 PJ4 jumper have any effect on fan speed when auxillary heat is called for or when the system goes in defrost mode and energizes the heat strip?
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Old 10-13-2009, 04:34 PM   #8
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Low speed fan heating?


No, It will remain on its high speed.
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Old 10-13-2009, 05:43 PM   #9
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Low speed fan heating?


Just curious here since I have never actually needed to run the heatpump in emergency heat mode. What would be the affect on the system if I were to cut OT2 PJ2 jumper?

Last edited by zep; 10-13-2009 at 05:45 PM.
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Old 10-13-2009, 06:12 PM   #10
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Low speed fan heating?


Then it runs in low speed when ever E, or W2 are energized.
So if aux heat is called for while the heat pump is running. It would slow the blower, and decrease the amount of heat you get from the heat pump.

The effect is the same for emergency heat, with either jumper cut. Slows the blower, so the air temp rise is higher, and you don't feel like cold air is blowing out the registers.
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Old 10-13-2009, 07:56 PM   #11
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Low speed fan heating?


Makes sense now. I appreciate your knowledge on this. It appears that cutting OT1 PJ4 jumper is the way to go. Happy that I did not just arbitrarily cut the wrong jumper. Thanks.
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Old 10-13-2009, 08:14 PM   #12
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Low speed fan heating?


No problem.

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