INSIDE FAN MOTOR

[NORMAN W KENNEDY]

HEIL MODEL PHD 448000KTP Unit has an intermittent problem, sometimes nothing runs -IFM, OFM and compressor. Then, when I go outside to the unit and start checking it out, it may start on it's own and function properly for a couple of days. My immediate question is: should the IFM run even if the the compressor and OFM will not run. I am trying to isolate the problem, and I cannot determine if it should run based on the wiring diagram and lack of information about the defrost board and IFB. Thanks for any insight.

 

[Fitter30]

First kill power to unit check all connections on boards, push on terminals (spade terminals like to crack) screw terminals, thermostat. Run two wires out of cabinet c & w1 thermostat connections. This way can check voltage to see if your getting 24 volts without opening cabinet. Have voltage probably has bad solder joint or connection on a board or relay. Open cabinet gently if unit doesn't start just gently tap relays and board connections with something that doesn't conduct electric.

 

[Sponsor]

 

[WorthFlorida]

The air handler fan and the outside compressor fan run independent of each other. The compressor fan along with the compressor run off of a relay (or contactor) on the outside unit. It's located under the access panel. The air handler fan usually is controlled by the thermostat. It will operate a relay or circuit on the control board inside the air handler. All digital and smart thermostats have a start delay between cycles. About three or four minutes after a heat or cooling cycle. It is to allow time for the compressor head pressure to decrease otherwise it can run backwards if the head pressure is too much. At startup motors have very little torque to push against high pressure. During this wait time nothing will run.

The picture below, the fan relay is in the air handler, the Y or W (for a heat pump systems) will operate the contactor on the compressor unit.

 

[NORMAN W KENNEDY]

Thanks, WorthFlorida, That is exactly what I wanted to know. I just wanted to know if the compressor and outside fan circuit could prevent the air handler fan from running. I didn't think it would, but I wasn't sure given the sketchy wiring diagram Since none of those are running when the unit is malfunctioning, it is something common to both circuits. It is running fine today.

 

[WorthFlorida]

Thanks, WorthFlorida, That is exactly what I wanted to know. I just wanted to know if the compressor and outside fan circuit could prevent the air handler fan from running. I didn't think it would, but I wasn't sure given the sketchy wiring diagram Since none of those are running when the unit is malfunctioning, it is something common to both circuits. It is running fine today.

The most common part is the 24v transformer. It's used for all relays and circuits including the thermostat. It would be rare that it is intermittent. It is why fitter30 suggested to check the connections. No 24v-ac, nothing work and it is in the air handler in the compartment where the 240v enters. The next time it all quits, you need a voltmeter to check it. If you have a non digital thermostat or a digital one that uses batteries, you cannot tell from the thermostat alone. The batteries keeps the display active. A WiFi thermostat, it will go dark because of no batteries.

Inside the air handler is a control board, it is where thermostat wires terminate to and the wires to the compressor unit. If this board fails it could prevent everything from working. Depending on the SEER rating and the confiscation of the unit it might even communicate with a control board on the compressor, such as Carrier's Infinity units. With either AC only or heat pumps, when the thermostat calls for heat, the control board signals the fan motor to run slower.

Do you have AUX heat, electric or gas? You mentioned a defroster. Does your unit have one on the outside coils?

You can buy the transformer on Amazon for about $10-$20 and I keep one in the air handler closet. SC I'm sure get a lot of electrical storms like Florida and the transformers go quit often. It is easy enough to check and replace. It could save a $150 service call and get your heat or AC up and running in a short time.
https://www.amazon.com/Control-Transformer-Primary-Secondary-Furnace/dp/B07RDBS6NK/ref=sr_1_5?crid=KKGRE8Q17VVK&dchild=1&keywords=ac+transformer+120v+input+24v+output&qid=1608952268&sprefix=AC+transformer,aps,196&sr=8-5