HVAC help

[Runs2rch]

Have a Lennox heat pump model number HP26. Worked great as always over the summer.

Went to fire up the heat last Friday. Fan motor running, but not the heat pump.

Diagnosed it to a bad defrost control board. Have a new capacitor and contactor as well to install.

My problem is the new defrost board which supersedes the old part number is a little different. I wired it up how it seems it should be, but not working. Finding any decent wiring diagram has been impossible. Hoping someone here knows.

 

[River Dirt 2]

you probably have this already but here it is for starters.

http://www.completeheating.ca/images/pdf/LennoxHP26.pdf

https://www.lennox.com/lib/legacy-res/pdfs/installation_maintenance/lennox_hp26_iom.pdf

 

[Flying_Lavey]

Post a picture of the old board (preferably before being removed), and one of the new board.

Sent from my LM-G710VM using Tapatalk

 

[Runs2rch]

Post a picture of the old board (preferably before being removed), and one of the new board.

Sent from my LM-G710VM using Tapatalk

New board is top pic. Old board is bottom pic. HVAC guy took old board with him. Not sure when he can come back. Might as well get it done myself.

 

[Runs2rch]

O, DF, Y1, and Fan are easily switched. High psi switch no problem. Jumper for Low psi since unit does not have one. I can take a pic of how it is in there in the am and post it. That way you can tell me what isn't right haha.

 

[Flying_Lavey]

And typical Lennox...... Odd labels and proprietary parts..... I did find a picture of the new board installed. If I was there I could quickly figure it out. Kinda hard to tell on the pictures without some sort of documentation.

https://images.app.goo.gl/nabFwH3EPM716oqf6

Sent from my LM-G710VM using Tapatalk

 

[Carlson-jet]

Just wondering if you tried the jumper in test?

 

[jet496]

Look at the schematic & bypass the board. Defrost is so rarely needed in California & you could simply switch it to cooling yourself to defrost if you had to.

 

[TrollerDave]

Have a Lennox heat pump model number HP26. Worked great as always over the summer.

Went to fire up the heat last Friday. Fan motor running, but not the heat pump.

Diagnosed it to a bad defrost control board. Have a new capacitor and contactor as well to install.

My problem is the new defrost board which supersedes the old part number is a little different. I wired it up how it seems it should be, but not working. Finding any decent wiring diagram has been impossible. Hoping someone here knows.

Do the diagnostic LEDs show anything?
What exactly isn’t working with the new board?

 

[Carlson-jet]

I'm going to add another thing. I wonder if the delay jumper is to run a few tests before final commitment?

I'm not an HVAC guy. But I have operated, rebuilt and maintained a few 3 million+ BTU ovens a few times and replaced banks of controllers.

 

[Runs2rch]

Do the diagnostic LEDs show anything?
What exactly isn’t working with the new board?

High psi switch fault. To me it looks like hvac guy ran high psi switch how it was on old board, not right next to each other like new board.

Waiting for the ran to let up. I can take the panel off and post a pic.

 

[Runs2rch]

And typical Lennox...... Odd labels and proprietary parts..... I did find a picture of the new board installed. If I was there I could quickly figure it out. Kinda hard to tell on the pictures without some sort of documentation.

https://images.app.goo.gl/nabFwH3EPM716oqf6

Sent from my LM-G710VM using Tapatalk

Just from the reading I have done that seems exactly it with Lennox. Rain is supposed to let up here. I will get a pic posted up as soon as it does.

 

[BajaT]

Perhaps the bypass line?!!!

 

[Runs2rch]

Here are the pics.

 

[Runs2rch]

Figured it out. Low psi jumper, and temp sensor to L and 24v. Purring out there now.

 

[TrollerDave]

So it needed the low pressure switch jumped?

Is that temp sensor the one on the discharge line (skinny copper line right in front of the compressor) with the 2 red wires?

Glad you got it working. Good job.

 

[Hava-Schiada]

Way above my pay grade! That’s why I have @slowinhavasu on speed dial!

 

[Flying_Lavey]

Figured it out. Low psi jumper, and temp sensor to L and 24v. Purring out there now.

I finally got a chance to look at all this (crazy day at work). Which temp sensor did you wire from the L and 24v? One (brown leads) is the defrost thermostat (initiates defrost when too cold and turns it off when warmed up) and the other thermostat is a little odd with its location being a thermal switch on the discharge line (typically you'd see a pressure switch for either a safety or for condenser fan cycling).

Also, do you have any reheat in the fan coil? When fully wired, the W terminal would energize the reheat during the defrost cycle if the thermostat is calling for heat. With that disconnected and that thermostat with the brown leads energizes the defrost, you'd get some nice super cold air as the system will switch into AC to defrost the coil and no secondary heat source to temper the air. Likely not much of an issue in So Cal at all but just something to keep in mind if the supply air gets super cold all of a sudden in the winter.

So it needed the low pressure switch jumped?

Is that temp sensor the one on the discharge line (skinny copper line right in front of the compressor) with the 2 red wires?

Glad you got it working. Good job.

There isn't a low pressure switch (safety) so that sensor circuit needs to be jumped closed as a low pressure safety will open the circuit when below operating range.

Sent from my LM-G710VM using Tapatalk

 

[Carlson-jet]

I knew it!!

I'm absolutely no help.

I do dig these threads with a good conclusion.

 

[Runs2rch]

I finally got a chance to look at all this (crazy day at work). Which temp sensor did you wire from the L and 24v? One (brown leads) is the defrost thermostat (initiates defrost when too cold and turns it off when warmed up) and the other thermostat is a little odd with its location being a thermal switch on the discharge line (typically you'd see a pressure switch for either a safety or for condenser fan cycling).

Also, do you have any reheat in the fan coil? When fully wired, the W terminal would energize the reheat during the defrost cycle if the thermostat is calling for heat. With that disconnected and that thermostat with the brown leads energizes the defrost, you'd get some nice super cold air as the system will switch into AC to defrost the coil and no secondary heat source to temper the air. Likely not much of an issue in So Cal at all but just something to keep in mind if the supply air gets super cold all of a sudden in the winter.



There isn't a low pressure switch (safety) so that sensor circuit needs to be jumped closed as a low pressure safety will open the circuit when below operating range.

Sent from my LM-G710VM using Tapatalk

So L and 24v is the thermal switch. Brown leads go to DF on the board. I don't think there is a reheat in the fan coil. In the pic I posted old board was supposed to be wired L to W for the thermal switch.

 

[Flying_Lavey]

So L and 24v is the thermal switch. Brown leads go to DF on the board. I don't think there is a reheat in the fan coil. In the pic I posted old board was supposed to be wired L to W for the thermal switch.

I woulda loved to have seen how that old board was wired. I imagine the L is for "limit switch". In this case that would be a discharge thermal limit. W is typically (in almost every single application ever) for heat so to run the thermal limit from the heat terminal is quiet odd. Unless it's a Lennox oddity and is quiet normal. Lol! I'm not familiar enough with Lennox products to say for certain.

Sent from my LM-G710VM using Tapatalk

 

[Taboma]

Just going to toss this out here Runs2rch --- May help sort this out, even if the unit #'s don't match up.
https://www.justanswer.com/hvac/71lqt-need-wiring-diagram-lennox-84w88-installation-system.html

 

[Runs2rch]

I woulda loved to have seen how that old board was wired. I imagine the L is for "limit switch". In this case that would be a discharge thermal limit. W is typically (in almost every single application ever) for heat so to run the thermal limit from the heat terminal is quiet odd. Unless it's a Lennox oddity and is quiet normal. Lol! I'm not familiar enough with Lennox products to say for certain.

Sent from my LM-G710VM using Tapatalk

I thought it was supposed to stand for service light. You are right. Lennox oddity for sure. That's why I was second guessing the wiring before I said FFF it and tried it.

 

[rrrr]

I used to have a couple of HP26 units. When one of them blew a compressor, I replaced it. Before it went on the service guy's truck, I took the board out so I would have a spare.

Since then the other unit has been replaced too, but I might still have the board. I'll look around, if I can find it you're welcome to it.

Edit: After reading the entire thread, i see you were able to make the new board work. Good job.