windowshaker heat pump controls hacking

u3b3rg33k · 04-20-18, 06:53 PM

I have a happy little frigidaire FFRH0822R1 - that's an 8k cap tube window mounted heat pump.

it works great down to 40F, where it switches over to the 1kW strip heat, providing less heat, and using more energy than it needs to. I can't fathom a reason they didn't implement defrost other than to save the cost of one additional motor, and an extra ten cents on the control chip.

I plan to re-do the controls (and the outdoor side fan) so that it can operate down to whatever point it is no longer useful. to do this I plan on ditching the factory controls entirely, and switching it over to 24VAC controls.
If anyone sees a flaw in my plan, please point it out to me.

I will be using a Honeywell prestige thermostat, because I like them. YTHX9421R5085WW

I have this defrost board 47D01U-843 due to a friend picking it up for his home system and then upgrading to an inverter split system, so I got a great deal.
It has a number of defrost modes, including a couple of demand modes, so I'll give it a go.

Please note that I do NOT want to open the refrigeration circuit. it's a dual cap tube currently, and has no issues working above 40F, so I see no benefit to messing with the charge/refrigerant choice. That's another idea, for another time in another thread.

Thermostat inputs
User demand
return temp
supply temp
outdoor temp

Thermostat outputs
Y (comp call)
O/B (reversing valve)
G (fan)
W (aux heat)

defrost board inputs
Y
O/B
air temp
coil temp

defrost board outputs
Y
O/B
ODU Fan relay
W for defrost heat

Logic provided by thermostat / demand defrost board
aux heat lockout
compressor lockout
defrost of outdoor coil
short cycle protection
outdoor coil temp sensing
outdoor air temp sensing

Things I won't have without further logic/sensors
protection against strip heat without fan (airflow proving)
low pressure cutout (no plans to implement)
high pressure cutout (no plans to implement)
outdoor coil fan (plan to cut off shaft and add in a 12V radiator fan(due to cost, ease of mounting, availability, and small diameter selection) that will be controlled by the defrost board fan relay.

I think they only remaining tasks will be swapping out the 120VAC reversing valve coil for a 24V coil, and adding a couple relays to trigger the 120V components.

Thoughts?

04-20-18, 06:53 PM	#1
u3b3rg33k Apprentice EcoRenovator Join Date: Mar 2018 Location: Rustbelt, USA Posts: 114 Thanks: 5 Thanked 10 Times in 9 Posts	windowshaker heat pump controls hacking I have a happy little frigidaire FFRH0822R1 - that's an 8k cap tube window mounted heat pump. it works great down to 40F, where it switches over to the 1kW strip heat, providing less heat, and using more energy than it needs to. I can't fathom a reason they didn't implement defrost other than to save the cost of one additional motor, and an extra ten cents on the control chip. I plan to re-do the controls (and the outdoor side fan) so that it can operate down to whatever point it is no longer useful. to do this I plan on ditching the factory controls entirely, and switching it over to 24VAC controls. If anyone sees a flaw in my plan, please point it out to me. I will be using a Honeywell prestige thermostat, because I like them. YTHX9421R5085WW I have this defrost board 47D01U-843 due to a friend picking it up for his home system and then upgrading to an inverter split system, so I got a great deal. It has a number of defrost modes, including a couple of demand modes, so I'll give it a go. Please note that I do NOT want to open the refrigeration circuit. it's a dual cap tube currently, and has no issues working above 40F, so I see no benefit to messing with the charge/refrigerant choice. That's another idea, for another time in another thread. Thermostat inputs User demand return temp supply temp outdoor temp Thermostat outputs Y (comp call) O/B (reversing valve) G (fan) W (aux heat) defrost board inputs Y O/B air temp coil temp defrost board outputs Y O/B ODU Fan relay W for defrost heat Logic provided by thermostat / demand defrost board aux heat lockout compressor lockout defrost of outdoor coil short cycle protection outdoor coil temp sensing outdoor air temp sensing Things I won't have without further logic/sensors protection against strip heat without fan (airflow proving) low pressure cutout (no plans to implement) high pressure cutout (no plans to implement) outdoor coil fan (plan to cut off shaft and add in a 12V radiator fan(due to cost, ease of mounting, availability, and small diameter selection) that will be controlled by the defrost board fan relay. I think they only remaining tasks will be swapping out the 120VAC reversing valve coil for a 24V coil, and adding a couple relays to trigger the 120V components. Thoughts?