Heating, Air Conditioning, Fridge, HVAC/Canít get 24V to contactor


Wiring diagram
Wiring diagram  
Goodman CPLE24-1A Condensing Unit on Heat Pump

Installed 2001, I believe itís a split system (air handler in basement with aux heat, condensing unit outside, forced air through ducts).

System worked fine last summer, sometime during winter must have started doing Aux Heat, when tenant started AC in spring had nothing.  Heat still works but outside unit doesnít come on, only air handler using aux heat only.  Air handler does not come on for cooling.  When I check voltage on either side of contactor I get zero when trying to heat or cool.

When I push contactor in, compressor and fan come on fine.  Had refrigerant pressure checked and itís fine, and resistance across wires from LP cutoff switch near zero (continuity beeps on the meter).

I also swapped out capacitor with like unit, and got a replacement control board (not OEM).  Neither made any difference.

I am getting 27V from wires coming from transformer.  I took wire nuts off and checked voltages (did not disconnect all the wires) when system set to COOL.

For Room temp 75, Desired temp 80 (cool off), I got 27V for these wire combos:

Red to White, Yellow, Blue
Orange to White, Blue
Yellow to Blue

For Room temp 75, Desired temp 70 (cool on), I got 27V for these wire combos:

Red to White, Yellow, Blue
Orange to White, Yellow, Blue

Guy that checked pressure maintains HVAC and electrical for small college campus, and he was stumped.

Parts breakdown here:
http://www.dnmech.com/lit/RP-278D.pdf (pages 6-9)

Am attaching wiring diag from condensing unit.

Appreciate any ideas on what to check.


Your suppose to have 24 volt ac at the low side of the transformer. ( R and C ) Try physically jumping out the low pressure switch to see if it will start. Just because you have refrigerant does not mean the LPC is closed. Your LPC ( low pressure control ) may be bad . Also above where it says WIRING CODE on the wiring diagram there is a optional ? Thermostat hooked to the Y wire looks to say LAC if you have that in your system jump that out also.Look at wiring diagram to see what other safety control is in series with the contactor and physically jump it out. You can also  jumper R to Y to O at the thermostat to see if cool come on.  R being one side of the transformer , Y  goes to one side of the contactor ( going through your safty controls )  O goes to one side of your reversing valve coil. The other side of the reversing valve coil and contactor goes to Common of the transformer. You can also touch the  R wire and the Y wire together  at the outdoor unit, your contactor should close, provided all your safty  did not trip.

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40+ years diversified experience.An HVAC/Refrigeration Self Employed Contractor since 1986. NATE Certifield. Answer questions pertaining to Residential and Commercial Air Conditioning , Warm Air Heating, Heat Pump systems.Mechanical and Electrical troubleshooting of these systems.Be as detailed as possible when describing problem.Packaged unit or split systems.No appliance questions.


Installation and Troubleshooting, Mechanical and Electrical, in following areas, Refrigeration ( Walk In and Reach In Coolers and Freezers ) Commercial Roof Top and Packaged Heating/Cooling ( Natural Gas,Propane, Electric, and Heat Pumps ) Computer Room Air Conditoning Systems,Commercial Residential Packaged and Split Systems Air Conditoning and Heat Pumps.Warm Air Oil , Natural and Propane Gas Heating systems.

Graduated from Private Technical School in 1975. An HVAC/Refrigeration Contractor . Have Unlimited Heating/Piping and Cooling Contractor License.Limited Sheetmetal Contractors License.NATE Certifield. York Certifield Master Heat Pump Technician 1986. Served 33 years combination Active Duty Air Force , Air Force Reserves and Air National Guard in the HVAC/Refrigeration Shop/Mechanical Shop. Troubleshooting/Installing HVAC/Refrigeration Equiptment Worldwide. Retiring in 2003 as a Senior NCO ,and a Mechanical Superintendent.

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