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airheatman
airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 8327
Experience:  Furnace, A/C and heat pump specialist.
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Xiaoning here. I have a lennox HP22-511-1p heatpump, the

Customer Question

hi Xiaoning here. I have a lennox HP22-511-1p heatpump, the outside unit is nor running
if i push in the contactor it ran fine but there is no voltage to the contactor.
Submitted: 2 years ago.
Category: HVAC
Expert:  airheatman replied 2 years ago.
Hello. My name is ***** ***** I'll do my best to help. Let's get started and see what we can do.Do you have a volt meter for troubleshooting and can you do some hands on?
Customer: replied 2 years ago.

Yes

Expert:  airheatman replied 2 years ago.
OK our first step is to start where the control wires first come into the outdoor unit.We want to locate the low voltage wires R and C from thermostat to outdoor unit.Check to see if we are getting 24 to 28 volts between those wires,If so we will concentrate on the outdoor unit.If not, we will concentrate on indoor unit ,thermostat and wires between units.
Customer: replied 2 years ago.

yes 24.7

Expert:  airheatman replied 2 years ago.
OK that means we are losing the 24 volts between there and the contactors. follow those two wires and see what is between there and the contactor coil.(Time delay,pressure switch,defrost board,etc.). If you can attach a photo of the wiring diagram label on unit, I can guide you.We need to determine which of those components is not allowing the 24 volts through to the contactors.
Customer: replied 2 years ago.

here is the wire diagram

Expert:  airheatman replied 2 years ago.
OK lets check at the defrost board. First check 24v between Com and 24v and then between COM and OUT
Customer: replied 2 years ago.

no voltage between com and 24 on cmc1, no valtage between com and out. there is a sensor in between the com and 24v on the borad, see pic (i pointed to it, it is attached to a copper tube.

Expert:  airheatman replied 2 years ago.
THat looks like a pressure switch. Can you shin the wires a bit and see if we have continuity through that switch?
Customer: replied 2 years ago.

what is shin?

Expert:  airheatman replied 2 years ago.
Sorry typo. Skin the sheathing on wires so you can take a continuity reading by touching probes to the bare wire
Customer: replied 2 years ago.

wires both way look ok i got continuity from them

Expert:  airheatman replied 2 years ago.
Anywhere else in that circuit where we can be losing the voltage? If we have 24 coming in, but not at defrost board. has to be a break in the circuit.
Customer: replied 2 years ago.

Anything else you think I can test or check out?

Expert:  airheatman replied 2 years ago.
Might try taking a fields provided control wire directly from where we have 24v over to the defrost board terminals.Sounds like we have a break somewhere in that circuit.
Customer: replied 2 years ago.

do you mean to bypass the switch?

Expert:  airheatman replied 2 years ago.
Yes as well as making sure there is not a breakdown in the wire.If we have 24v at one spot and not at the defrost board, something has to be "open" between them
Customer: replied 2 years ago.

bypass the switch got power at 24v terminal of the defrost board but not at the out

Expert:  airheatman replied 2 years ago.

Is there any other switch that is wired into the defrost board like a low presure switch attached to suction line, that has to prove closed for defrost board to allow power out. If so, it would be marked something like LP IN and OUT. If so, that would have to also be closed (continuity) for the defrost board to send signal to contactors.

Customer: replied 2 years ago.

I don't see them. I include two pictures for the board

Expert:  airheatman replied 2 years ago.
I am thinking may be that little time delay board marked tD1, but I dont have a diagram showing me exactly how wiring should be. I will open to other experts who may be able to direct you in checking it.
Customer: replied 2 years ago.

thanks a lot

Customer: replied 2 years ago.

just wondering if any expert has some thoughts on my issue.

thanks

Xiaoning

Customer: replied 2 years ago.

I am still stuck here, any update?

Thanks

Xiaoning