Heat Pumps and Electric Heating - Contactor not pulling in.

I'm no stranger to electrical controls...I build custom automated control panels for a living. However the heat pump is very humbling! Finding information and schematics for my system has been quite a search. Not to mention I've never given much thought to HVAC work , operation or theory. For nearly 40 years the only thing I've done with HVAC is adjust a thermastat and change filters. If anyone can throw me a bone I would humbly accept and regard you as my heroe!

Problem... The heatpump fan and compressor (outside) are not coming on when the thermastat and airhandler/furnace come on inside. When the signals are sent... the outside unit clicks a few times and the blades meagerly turn a few inches.

I have an Intertherm heat pump outside (model T2RC 030k)
and my defrost board is part # DFORB-AB1004.

I've checked my thermostat wiring to the air handler and from there to the heatpump defrost board. Even drawn a schematic of all the interconnections between the three for the next time fate has me crawling around in the laundry room. :)

At the defrost board with the inside thermostat set for cooling and all my breakers on. I have 24 volts present at ("Y", "O", "E", and "R") I have no voltage present at ("C" or "W2") I have a pressure switch and it shows OPEN. I have no voltage present at the coil of the contactor. If I manually press the contactor in the fan turns and the compressor works (I feel the copper tubing get ice cold and begin to collect condensate) Have I trouble shot the system sufficiently to determine that the control board is bad and that the single starting capacitor is indeed good? Or did I miss a trouble shooting step. I'm a complete newbie to HVAC repair. The replacement board I have found is $60 and is a ICM302. At the moment I have the Wire that belongs on the "Y" terminal run straight to the coil on the contactor to keep the contacts pulled in. Which will see me through a few days of spring/summer outside temps... but I want to have everything correctly working again soon and definately before fall/winter temps.

BTW as I understand the Y,O, E, R, W2 and C terminals...
Y= Signal for cooling compressor relay
O= signal to revers valve on heat pump
E= signal for emergency heat
R= 24volt control power
W2= Signal for heat 2nd stage
C= Changeover (?)

Thanks for any and all advise.... and hoping my experiences will make it easier for the next person with an intertherm heat pump.... this is becoming quite a fun/disturbing lil' puzzle! <grin>

Marty - K4MLW

C= commen, is this pressure switch a high pressure switch? Is it located on the Refrigerant piping?

C= commen, is this pressure switch a high pressure switch? Is it located on the Refrigerant piping?

"C" for common ... that makes sense! Thanks. I was using the ground terminal for reference. have rechecked my voltages using the "C" terminal for reference and still measure the same.

Re: The pressure switch... I haven't taken the fan guard/grill off of the heat pump so I can't actually reach down into it and inspect it closely. I was assuming it was a pressure switch. Now that I'm replying to you... I've gone and looked again and the two red wires travel back to the defrost board and connect to terminals "R" and "DFT" :wall: I now believe that is is no longer a high pressure switch but a thermistor to sense the coil temperature and allow a 24Vac signal to the "DFT" terminal to initiate the Defrost timer/sequence.

In a sick sorta way this unexpected heatpump project is somewhat facinating.... maybe one day I'll be a HVAC installer. <grin> I'm nearly 40 and still don't know what I wanna be when I grow up. :cheshire:

Marty

I think you are close to the problem. Either you have a bad sensor, such as a high presure cutoff sensor, or some other sensor; or it is your board as you originally thought. FYI, a temp senor would merely be strapped to the line whereas a pressure switch would be an integral brazed part to the lineset.

Got either of those, or something else?

I think you are close to the problem. Either you have a bad sensor, such as a high presure cutoff sensor, or some other sensor; or it is your board as you originally thought. FYI, a temp senor would merely be strapped to the line whereas a pressure switch would be an integral brazed part to the lineset.

Got either of those, or something else?


Nope... the only wires inside the heatpump... go to the reversing valve, the defrost sensor mentioned above, the compressor and of course the fan. There are plenty of wires outside the pump housing in the controls area near the defrost board. Attached to the contactor, capacitor and the defrost board. But none go to any of the refrigerent tubing other than the above mentioned reversing valve and defrost sensor.
just found the ICM302 board in town and in stock... for $55 Think I'm going into town forawhile with what I hope to be the answer. Post more later with good news I hope! Post more later otherwise as well. :)

Thanks again this forum is great!
Marty - K4MLW

So we know your problem is with the low voltage cooling circuit "Y", or so it would appear. 24v into board nothing coming out? You bypass the board and all is fine, without seeing it I would say its new board time.

So we know your problem is with the low voltage cooling circuit "Y", or so it would appear. 24v into board nothing coming out? You bypass the board and all is fine, without seeing it I would say its new board time.

Yep.... that did it. Made the chore of driving into town a bit more fun by riding my dualsport motorcycle. Slid by the elementary school to grab my son. He was excited to get to ride. Even though I had my volt meter telling me I had everything off! I had my son sit near by on porch while I swapped the boards being careful to stay away from the 220Vac on the contactor the whole time. Got it swapped and flipped all the breakers back on.... swung the arm on the thermostat and EUREKA!:) We're back in business. Thanks so much to everyone in the forum and especially the folks kind enough to respond with advice. This has been a very satisfying adventure in home maintenance.

****Disclaimer I'm a newbie to HVAC repair and dangerous voltages are behind every panel I messed with today!.... I'm an automation tech by trade and felt humbled by the heatpump system at times. know how to use your volt meter and practice electrical safe working habits.. especially around the contactot and the startin capacitors... and don't sue me if you kill yourself doing what I did in this post.... namely cause I'm so poor I have to fix my own heat pump... so your lawyer wouldn't get anything outta me anyway ;) *********

For those searching the forum in the future...
I have a Intertherm heat pump model # T2RC-030K that wouldn't do anything but click a few times and move the fan blades a few inches when the thermastat called it to run.
I checked all wiring between thermastat, furnace and heat pump... and fixed a few places that had been gnawed on. (mice?) according to the furnace schmatics (where the 220 pri to 24 Vac secondary x-fmr is located) I had the correct voltages on the signal wires going outside. With meter in hand I went out to the heat pump and found where the signals wires went into it. I had the correct voltages on the input terminal on the defrost board also. At this point it could have been the contactor, the started capacitor, the defrost board itself or maybe the reversing solenoid valve... and possibly a few other things I'm not aware of. (I don't have a high pressure switch on my unit) I discharged and then tested the capacitors... then I manually engaged the contactor. when the contacts closed the unit made its usual squeak and began spinning the fan and operating the compressor. (Copper tubing got cold in less than a minute proving the compressor was functional ) That left me with possibilities of a bad control board or faulty coil on the contactor.... and again possibly several other things I'm not aware of... cause I'm not a HVAC pro... just a frugal homeowner. I used my volt meter to see if the contactors coil was getting 24Vac to pull it in and it wasn't. So I took the Yellow wire (yellow on my system) that was at the "Y" terminal of the defrost board and rerouted it directly to the contactor coil. The 24Vac signal present on the yellow wire was enough voltage and current to energize the coil sufficiently to pull in the contactor and my unit was TEMPORARILY running. At this point I figured as others in the forum that the problem was indeed my control board. I bought a new board locally (Part # ICM302c) for about $50 and swapped it out.... by placing all wires where they originally were.<old board vs new. Turned all my breakers back on and the system is operating like she had for the past 13 years. After it gets the house cooled back off... I'll turn it off for awhile and check all the heating functions.... but for now she is pumping cold air and WE ARE HAPPY!

Thanks again to all the forum members and sponsors... This forum... like all forums are only as good as it's participants and this one is great!Beer 4U2

Marty - K4MLW

Glad to hear a new board fixed it, but you did most of the diagnostic work yourself.

I'd say there is no thanks needed since by doing a great job of describing the problem and the follow-up for those with future problems is your payment forward.

I agree with "dac" you thought it through (thats the hardest part) and were on the right track. Beer 4U2