Nordyne e2eb series furnace with heat pump

farmersam

I have a 20 year old Nordyne e2eb series electric furnace. I rcently replaced my a/c with a heat pump. Everything works BUT when the Tstat calls for either heat or cool from the heat pump the blower fan activates on high speed. I have a Honeywell RTH6500wf series Tstat. The furnace does not have a control board. All it has is a 4-wire pigtail and an NO fan relay and an NC fan relay. The heat pump only has 5 terminals: Y, B, D (this poses another problem I'll get to in a minute), R, C. I assume that the reason the blower only comes on at high speed when the heat pump is running is because when the Tstat energizes the Y terminal it also enegizes the G terminal. And since all I have at the furnace is a green wire coming out of the pigtail, and there is no way for the furnace to know if the Tstat is calling for Heat or Cool, it is hardwired to run the blower on high speed either way. I can't figure out any way to fix this problem with what I have to work with other than manually switching the fan speed wires on the fan relay based on whether I am heating or cooling. plus, as mentioned earlier, without a D terminal on the furnace the HP has no way to call for aux heat when in defrost mode. I realize the Tstat will eventually call for aux heat once the room temp falls 2-3 degrees...
My question is: Is anyone out there familiar with the Nordyne P/N 902987 A/C Heat Pump (4-7 wire) Relay Box that is made for the e2eb furnace? And if so, will adding this option give me what I need to remedy my issues? Or will it still not solve the problems?
Or, is it possible to solve the fan speed issue by changing some wiring on the setup I currently have. (I do have a couple unused communication wires.) And can I solve the Defrost issue by running a wire from the D terminal at the HP to the white wire at the furnace pigtail? I already have a white wire from the Tstat Aux/Em Heat terminal to the white at furnace pigtail. That way the Aux Heat could be energized from EITHER the Tstat OR the HP. Does that work?? (That would also mean the D terminal on the HP would be energized any time the Tstat called for Aux/Em Heat. Is that a problem?Sorry this is so long. I've always found that if something can be said in 10 words or less, I need 500. Ha,ha! Or, is there a BETTER control board I can add to this furnace??

pedmec

just post a picture of wiring diagram. most likely on back side of cover

EBEBRATT-Ed

It's easy as far as the fan wiring

Just use a dpdt relay.

Your power wire for the fan power for cooling to goes to the relay common terminal (constant 120 volt hot). The cooling speed for the fan motor higher speed terminal would go to the Normally open contact on that relay. Thats one relay pole

Your lower speed fan wire (heating) would get wired to the Normally closed contact on the other relay pole.
The wire that runs the fan now (that starts the fan) gets wired to common on that same relay pole

The coil of the new relay 24 volts 1 side is common 24 volt the other side is G from the thermostat.

During heating the relay is not powered and the motor get powered as it does now

farmersam

Attached is a wiring diagram...

farmersam

You say to use a dpdt relay. How is that any different than the NO and NC relays I'm using now?