I have an electric International Comfort Products HVAC unit Model # NFCP2400C2. It was working fine in air conditioning mode and I generally leave the blower fan in always on mode.

When I switched to heat mode, the unit came on ok but the heat and fan got stuck on. I disconnected the thermostat on the wall but the fan and heat stayed on. I had to power it off at the circuit breaker because it got so hot.

I left it powered off at the breaker for a while and opened it up and made sure the connections were tight and wiggled some wires. When I powered it back up it worked for a bit but the heat got stuck on again. After powering it off at the breaker, I set the thermostat to heat but set the temperature at the lowest setting to prevent the heat from coming on at all. It has been running ok in fan only mode for weeks.

It seems like a sticking relay to me but I can't figure out what part to replace. I had an HVAC repair person out about a year or two ago and they ended up replacing the main control board but it took them a few tries to get it right. It worked for a while after that.

I see the main control board inside the unit but there are a few other parts in there. One looks like a transformer and there is another black part that has wires coming into the top and sides which could be a relay but I cant see part numbers without taking things apart. There are at least 5 wires connected to that part (picture attached at the end).

Any suggestions as to what needs to be replaced? I have looked on parts sites and I can't find anything identified as a fan / heater relay.

I still believe that if I switch to A/C mode that the A/C will not get stuck on regardless of the thermostat setting. The heavy lifting for A/C is the unit outside anyway. This is electric heat so there must be a heavy duty relay somewhere for the heater coil. I just recently replaced the thermostat and the actual thermostat completely disconnects from the wall base when I remove it but and the heat continues to run so I it should not be a thermostat issue. I guess it could be crossed wires between the hvac unit and the thermostat but that does not appear to be the case based on a bit of testing I did.

Thanks,

 

Welcome to the forums.

The part that you are trying to describe and that is probably defective is the sequencer. It controls the heating elements and the fan. It is a relay of sorts.

As I look at what I think is the manual for your unit.... I don't see a sequencer. I see relays for the heating elements which means the fan is controlled from the electronic control board.

Since you are getting heat and the fan.... it appears to indeed be a sequencer.
Can you shoot a better picture of that relay above ?

manage my life/mmh/list/INSTL/L0502499.pdf

 

I can try to get better pics but I will have to go back up in the attic and open the unit up again...Here are some more pics that I already have of the control board, what appears to be a transformer, and the label on the cover.

 

On that ID tag.... the installer was supposed to check off what heating element system you have installed inside the air handler. Without that you will have to go inside the air handler and examine the "sequencer" for a part number.

 

I took better pics of the sequencer and ordered a 15SH2 style sequencer for about $20. Hopefully that does the trick. Here are the better pics of the heater coil info and the sequencer.

 

Did it work OK before you replaced the Tstat,will it work on heat if the fan is set to auto at the Stat?

 

Good picture. I'm fairly certain that will take care of your problem.