Split power to air handler?

[mattinnc]

Would it be possible to split the power to an A/C air handler? More specifically can I get the fan and the heating element on separate circuits?

I have an 11kw generator feeding an automatic transfer switch & 16-Circuit load center sub-panel. This will handle the Heat Pump A/C unit however it will not handle the additional load of the heat strip within air handler. I need to power the air handler to get the A/C fan to run. If I could get the fan and heat strip on separate circuits, I could include the fan and condenser circuits and have the A/C running during an outage.

 

[fitter30]

Yes you can power the elements separately. Most ahu the heat package come separately and in different kw's. Some come with their own breakers with the heat package.

 

[PoorUB]

Just put in a relay that disables the strip heat when the utility power is down. We did this often when I sold generators.

 

[mattinnc]

That is what I was hoping to do but it wont work for my situation. I have a 100 Amp sub panel that will have all the circuits powered by the generator. I cant move the 100 amp Air Handler circuit to that panel with the other circuits, it would be too much when on house power. If I could have a 15 or 20 amp separate circuit for just the fan in the air handler that would be OK.

 

[Phuckin' Jim]

In the context of an emergency outage, you could remove the access panel from the furnace and temporarily disconnect the heat strips. Unless you experience several outages a year.....

 

[PoorUB]

That is what I was hoping to do but it wont work for my situation. I have a 100 Amp sub panel that will have all the circuits powered by the generator. I cant move the 100 amp Air Handler circuit to that panel with the other circuits, it would be too much when on house power. If I could have a 15 or 20 amp separate circuit for just the fan in the air handler that would be OK.

How far is the transfer switch from the air handler?

 

[justinjoyal]

Just put in a relay that disables the strip heat when the utility power is down. We did this often when I sold generators.

This ^^ .

That'll work if you have two separate panels, one fed by the generator and one that's not.

Get a NO relay with a 120v coil powered by the panel that is not fed by the generator and run the "W" wire (most likely) from your thermostat through it, so when the power goes out, the relay opens and the air handler will not get a signal to turn on the electric strips.

If your generator feeds only one main panel and runs everything, you're gonna have to possibly rewire the electric heat kit so the fan and control board are fed by one breaker and the electric strips are fed by another one.

 

[PoorUB]

This ^^ .

That'll work if you have two separate panels, one fed by the generator and one that's not.

Get a NO relay with a 120v coil powered by the panel that is not fed by the generator and run the "W" wire (most likely) from your thermostat through it, so when the power goes out, the relay opens and the air handler will not get a signal to turn on the electric strips.

If your generator feeds only one main panel and runs everything, you're gonna have to possibly rewire the electric heat kit so the fan and control board are fed by one breaker and the electric strips are fed by another one.

There is utility power, at the transfer switch. Just run wires from the air handler to the transfer switch and mount the relay there. The control wires for the air handler are 24 volt and can be run in thermostat wire as long as the run isn't very far.

 

[justinjoyal]

There is utility power, at the transfer switch. Just run wires from the air handler to the transfer switch and mount the relay there. The control wires for the air handler are 24 volt and can be run in thermostat wire as long as the run isn't very far.

Yeah of course if it's accessible and there's space to mount the relay that'll work just fine.

 

[mattinnc]

....
If your generator feeds only one main panel and runs everything, you're gonna have to possibly rewire the electric heat kit so the fan and control board are fed by one breaker and the electric strips are fed by another one.

^^

This is what I am trying to understand how this would be done, I think it's will work best for my situation.

How far is the transfer switch from the air handler?

about 30'

 

[PoorUB]

^^

This is what I am trying to understand how this would be done, I think it's will work best for my situation.

about 30'

Don't rewire the air handler to two separate panels. You will need to rewire the internal wiring of the air handler to make that work and I can see that creating more issues.

Like the other post, wire a relay so the coil is wired to utility power and the contacts across the thrmostat wire that calls for heat, generally the W terminal. If the utility goes out the relay contacts open and drop off the W wire and you will not get resistivity heat.

 

[mattinnc]

The relay was the first thought and the transfer switch has a micro switch that could be used to break the thermostat wire that calls for heat. Initially that's what I was hoping to do.

Unfortunately the transfer switch is a sub-panel off a 100 Amp breaker on the main panel. The Air Handler / Heat strips are on a 100 amp breaker in the main panel. I know its using less than 60 amps when the heat is called for but add just a few more circuits and it maxes out the 100 amp breaker. So moving the 100 Amp breaker to the 100 amp sub-panel would not work. It actually would be OK when the generator is supplying power (using the micro switch) but when on utility power it would max out the 100 amp breaker to the sub-panel.

 

[jlv03]

Make/model of air handler? Any schematics to share?

 

[mattinnc]

Sure, it's a Carrier Model FV4CNB006. I was able to find the cooling only schematic (same one that is attached to the fan motor) and the heating element schematic.

I also found this in the installation manual of the Model FV4C Fan Coil units:

. Line- Voltage Connections
If unit contains an electric heater, remove and discard power plug
from fan coil and connect male plug from heater to female plug
from unit wiring harness. (See Electric Heater Installation
Instructions.)
For units without electric heat:
1. Connect 208/230v power leads from field disconnect to yel-
low and black stripped leads.
2. Connect ground wire to unit ground lug.

Makes me think if I could find the power plug for the fan coil, it might make things easier.

 

[fitter30]

Heater diagram black, yellow,blue cap off going to plug in strip.
Plug 3 carrier ahu is there a male plug with wires to feed power?
If not feed power to yellow and black at transformer. Condenser on its own breaker.
Probably 15 amp to ahu and what is the kw of heater? Heaters powered from terminal block. Could always kill one element when generator runs.

 

[PoorUB]

Sure, it's a Carrier Model FV4CNB006. I was able to find the cooling only schematic (same one that is attached to the fan motor) and the heating element schematic.

With only a 100 amp transfer panel this may be difficult! With the ECM motor and the one control board running everything I wonder if you can separate it out.

I was thinking you could run a feed from the house panel to feed the resistive elements, but there is a bit more to it. As there is line voltage going back to th AHU when the heat is one, probably to tell the motor the heat is on???

 

[mattinnc]

Plug 3 is actually a power plug directly on the fan motor, wired back to Plug 2 (pictured), where the heating element connects. Should be a good place to feed power for the condenser circuit. Thanks! I really appreciate the help!

 

[PoorUB]

Looking at the wiring schematic, (white background with blue printing) My concern is the blue wire running from after the heat contractors, going to terminal #11 on the 12 pin plug. Where does that wire go after it passes through the plug?

Also the yellow and black from the L1 &L2 terminal bock that goes to the 12 pin plug. Pretty sure that feeds the AHU side, blower motor and controls. Separate the wire the at the L1 & L2 terminal block and feed 240 volt from that point on a 20 amp circuit from the transfer switch and the heat side from the house panel.

Put a large caution label on the outside of the air handler that there are two separate 240 volt feeds for the next guy that comes long to work on it!!

 

[Jim greengo]

Would it be possible to split the power to an A/C air handler? More specifically can I get the fan and the heating element on separate circuits?

I have an 11kw generator feeding an automatic transfer switch & 16-Circuit load center sub-panel. This will handle the Heat Pump A/C unit however it will not handle the additional load of the heat strip within air handler. I need to power the air handler to get the A/C fan to run. If I could get the fan and heat strip on separate circuits, I could include the fan and condenser circuits and have the A/C running during an outage.

That's how most of them I come across are done.

 

[mattinnc]

Sorry for the slow reply, I was on vacation.

My concern is the blue wire running from after the heat contractors, going to terminal #11 on the 12 pin plug. Where does that wire go after it passes through the plug?

The blue wire does not pass thru the plug. It comes from the contactor to the plug however there is not corresponding wire that it connects to on the other side of the plug.

 

[LS6 Tommy]

3.5T heat pump will need about 10kW just to start the compressor...

 

[mattinnc]

3.5T heat pump will need about 10kW just to start the compressor...

I plan on installing a soft starter to limit the starting amp load.

 

[LS6 Tommy]

I plan on installing a soft starter to limit the starting amp load.

I wouldn't recommend that on a motor that's not inverter rated...

 

[mattinnc]

I wouldn't recommend that on a motor that's not inverter rated...

Talking with a few companies that makes these..they are specifically for scroll type compressors, which is what I have.

 

[LS6 Tommy]

Talking with a few companies that makes these..they are specifically for scroll type compressors, which is what I have.

OK, I get it. It's not a VFD type device, I guess. I don't do much with residential stuff anymore.

Tommy