requirements for variable speed thermostat?


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Old 05-30-11, 06:34 PM
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requirements for variable speed thermostat?

Hello,
I recently bought a house with a Carrier air conditioner and I'm curious to know if I could benefit from something newer than the current Honeywell round model (with mercury). The air handler is model number FK4CNF002, and based on the audible ramp-up/ramp-down of the blower when it switches on and off, I believe it has a variable speed motor.

How can I confirm that my system does indeed support variable speed operation - or is the model number on the outside of the air handler plus the ramp-up/ramp-down sound sufficient?

Based on some research, I think that a more sophisticated thermostat (like the Honeywell IAQ or perhaps something from Carrier) would allow me to run the system at different speeds to better control the temperature, reduce humidity, and save energy. Is this correct? And what are some of the top thermostats I should consider?

Thanks for any assistance.
 
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Old 05-30-11, 07:13 PM
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it does have variable speed. Changing thermostats wont do much unless you replace with a high end stat that controls humidity through sending a signal to cause blower to slow during a/c operation to help lower humidity, this will lower the efficiency of the unit though.
 
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Old 06-01-11, 08:59 PM
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Thanks for the reply. The outdoor unit is a Carrier #38TRA030320. How can I determine if this is 1-stage or 2? And does that matter for the installation of higher end thermostat?
 
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Old 06-02-11, 03:27 PM
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it is 1 stage a/c so it will make no difference on high end stat..... I recommend Vision Pro IAQ by Honeywell
 
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Old 07-31-11, 09:00 AM
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Honeywell IAQ settings for dehumidify?

Hi,
I went ahead and purchased the IAQ and wired it according to the "typical hookup of variable speed blower for dehumidification" directions, where DHM2 on the EIM is connect to DHUM on the air handler and a jumper connects DHM1 to R.

Things seem to be working as expected with 0379 set to 1 (dehumidify with air conditioner) but I'm curious to see if this is correct. I tried setting this to 3 (whole house dehumidifier) and 0384 to 1 (system fan turns on with dehumidifier) but that just runs the fan in a very low speed without engaging the compressor when the IAQ calls for dehumidify.

According to the carrier manual, the dehumidify function starts when the humidistat opens the contacts, which I believe is the behavior when 379 is set to 1.

Is my understanding of this configuration (and my current setting of 379=1) correct for my carrier FK4C?

Thanks for any pointers.
 
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Old 07-31-11, 09:16 AM
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correct 379=1........................................ set your aux cph to 3.... I know that the book says 9 for electric, but you wont like how often it cycles at 9 or the electric bill with it set to 9
 
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Old 07-31-11, 06:17 PM
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Thanks for the quick reply. I'm actually using a separate thermostat for heat (gas/hydronic) but what's the recommended CPH setting for the AC?
 
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Old 07-31-11, 06:22 PM
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The recommended cph for ac is also 3.
 
 

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