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 Repairing and Servicing Lennox Products
 Repairing / Servicing Lennox Heat Pumps
 Lennox 12HPB Series won't run
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Tom-in-the-heat

3 Posts

Posted - 06/21/2011 :  07:13:39 AM  Show Profile  Reply with Quote
Last Friday the compressor on my heat pump stopped working. Wife called me and it was 95 degrees in the house. I checked it out and found two things. First, the capacitor looked a bit swollen and second the contactor wasn't getting pulled in. I checked to make sure the control board had 24VDC coming in to throw the contactor (I didn't check it at the contactor). I checked it at the R (red) power terminal and the Y1 (yellow) compressor terminal. 24V present, contactor should have pulled in. So I pushed it in manually and would only hum. I figure i've got a bad capacitor and a bad coil in my contactor.

Purchased new 45+5 370VAC capacitor and new 30AMP SPST contactor (good replacements). Powered everything down and installed new capacitor and contactor. Powered everything back up. Set inside unit to "Auto" "Cool" and set thermostat at 70 degrees (inside temp 93). Waited 15 min and the outside unit never came on. Checked all connections twice.

Finally I decided to manually push in the contactor...this time with the new capacitor it worked and the fan and compressor came on but as soon as I let it go contactor released (no 24VDC to the coil I guess). So, I stood there scratching my head for a min then decided to check the voltage again. 24V coming in at R and Y1, nothing at the contactor or on the board at Y1 out and Y1 common.

The board has two red diagnostic LEDs and they are both simultaneously flashing, which means normal operation. I have to of these units and the other one is running fine and shows same light display. My gut reaction is to change the board but I don't think that's the problem...any thoughts?

Cozy.Support

5773 Posts

Posted - 06/21/2011 :  08:18:37 AM  Show Profile  Reply with Quote
Your measuring the voltage incorrectly. Check for 24 VAC between Y and C at the low voltage terminal strip outside. This is the voltage that turns the unit on. Sounds like your not getting 24 VAC from the thermostat control circuit to turn the unit on. You can confirm this by taking the voltage measurement between Y and C.



CozyParts.com, Inc. is an Independent Lennox Dealer providing a national parts distribution resource for Lennox parts since 2002. The Cozy.Support team does not provide a diagnosis for users of this forum. We do, however, try to provide information that will help servicers arrive at their own diagnosis.

Once you know what part you need, you can contact the Cozy parts department by using the link below
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Tom-in-the-heat

3 Posts

Posted - 06/21/2011 :  12:59:26 PM  Show Profile  Reply with Quote
Here's a good diagram of the wiring
http://www.lennox.com/pdfs/installation_maintenance/Lennox-12HPB-IOM.pdf
On page 5 (Figure 6)

So help me out here...R (red) supplies power to the board and C & Y1 are what is used to close and open the circuit?

If I understand the diagram correctly it would be the thermostat that is the problem, correct?
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Cozy.Support

5773 Posts

Posted - 06/21/2011 :  3:38:08 PM  Show Profile  Reply with Quote
If your not getting voltage to C and Y (24 vac), its either the thermostat or the thermostat wiring.



CozyParts.com, Inc. is an Independent Lennox Dealer providing a national parts distribution resource for Lennox parts since 2002. The Cozy.Support team does not provide a diagnosis for users of this forum. We do, however, try to provide information that will help servicers arrive at their own diagnosis.

Once you know what part you need, you can contact the Cozy parts department by using the link below
http://www.cozyparts.com/Lennox-Parts/locator_form.aspx
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Tom-in-the-heat

3 Posts

Posted - 06/21/2011 :  7:07:49 PM  Show Profile  Reply with Quote
Rechecked voltage as you recommended and sure enough no 24VDC to the board. Installed new Honeywell Pro 3000 series non-programable 2 Heat/1 Cool mulitstage heat pump thermostat and "BAM!!!!" I got air!!!! Thanks to you and my friend Andy "The AC Yoda" I have AC once again! Really appreciate all the help. You guys know what your talking about.
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