How to Wire a Heat Pump for AC Only:7 Facts You Need to Know

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Wiring a heat pump for AC-only requires connecting the thermostat’s Y and C wires to the outdoor unit for cooling operation, ensuring electrical compatibility (24V AC). Bypass heating wiring by omitting W connections, focusing on R (power), and G (fan), ensuring compliance with electrical codes, and verifying system SEER efficiency for optimal performance.

In this guide, we’re going to give you all the detailed steps and tips that will help you wire specifically what’s necessary to convert a standard dual-mode heat pump into an appliance that cools exclusively.

Materials and Tools Needed

How to Wire a Heat Pump for AC Only

To get started on this project, make sure you have the following:

  • A 5-ton heat pump unit (minimum capacity) from your brand of choice with full technical specifications
  • Three bundles of 8 AWG copper wiring that has THHN insulation
  • A four-pole 30-amp circuit breaker that’s meant for use with disconnect switches
  • A non-fusible disconnect switch (make sure it meets NEMA 3R standards), which should come in an enclosed package you can lock in the off position
  • A 24-volt transformer with a minimum of 75VA capacity  
  • Assorted nuts, crimp connectors, cable ties, and electrical tape for securing connections
  • A digital multimeter designed for measuring up to 600 volts AC/DC
  • Wire strippers suitable for working with 8 AWG copper wire
  • A voltmeter so you can measure incoming power supply
  • An electrical grade non-conductive fish tape that’s at least six feet long
How to Wire a Heat Pump for AC Only

Image Credits: Heat Pump Installation by Phyxter.ai is licensed under (CC BY 2.0)

Safety Equipment: Safety glasses, work gloves, headlamp.

Tools: Phillips and flathead screwdrivers. Pliers. Cable cutters. Hacksaw with metal cutting blades. Hammer. Power drill with assorted bits.

Step-by-Step Guide

How to Wire a Heat Pump for AC Only

Here are the steps involved in wiring a heat pump unit just for cooling mode:

Disconnect Power Supply

  1. Seek out and turn off both main breakers that supply power to the heat pump in the existing disconnect switch/circuit breaker box. These breakers should be 30 amp and 240V each.  
  2. Use a non-contact voltage tester to check that all electricity is off before continuing with any work. Warning – risk of electrocution!

Access Control Board and Wiring Compartment

  1. Remove the top service access panel from your heat pump unit so you can see the control board and main wiring compartment inside it.  
  2. Take care when removing insulation or debris that may be blocking your view.
  3. Disconnect any thermostat wiring connections that are already connected and cap wires not in use individually, verifying they have no voltage by using a multimeter.

Install New Thermostat Wiring

  1. Run five strands of new 18 AWG thermostat wire through into your house from the outdoor unit, leaving at least two feet of excess wire inside the heat pump’s wiring compartment.
  2. Clearly label the ends of wires as R, Y, C, G, and W1 using electrical tape.
  3. Connect labeled wires to matching terminals on the control board (compressor = Y; fan = G).

Modify Control Board Settings

  1. Find dipswitches or breakers on the control board that turn heating components on – they will probably be labeled W1, O, or B.
  2. Flip dipswitches to the OFF position/remove fuses to deactivate heating functions so only the cooling circuit is energized.

Install Electrical Disconnect

  • Mount the new 30A non-fused disconnect switch somewhere accessible within the line of sight according to local codes.
  • Set up 8 AWG copper wiring through the weatherproof conduit from the combined circuit breaker panel through the new disconnect switch and terminate it inside the heat pump unit by connecting it properly there too.

Connect Wiring

  1. Hook up 8 AWG wires to the contactor’s line side while making sure polarity matches – L1 to Line 1, L2 to Line 2, and Ground to GND lug. Warning! Verify ground connection first.
  2. Secure and seal loose wires inside the wiring compartment, then provide stress relief so that no conductors are exposed.

Power Restore and Testing

  1. Finally, turn on the 30A dual line breakers supplying power to disconnect the switch as carefully as possible.
  2. Make sure to turn on the switch and power up the heat pump. If everything’s good, a light should come on the unit control board.
  3. Switch it over to cooling mode now and drop the setpoint below room temperature. After a short delay, the compressor and condenser fan will kick in- then you’re officially in business! Be careful though, if that compressor goes below 40 degrees F of ambient temperature, you could risk damaging the equipment.
  4. Bring your thermostat back up past room temp to end cooling calls, and flip off that heat pump switch we had your turn on earlier. Lock it tight with a padlock so no one can mess with it without permission.

And just like that- You’ve got yourself a nice little cooling system! But remember to always let a professional handle dangerous electrical work, and adhere to local building codes before making any modifications.

Reference: Thermostat