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AC Installation Guide - 9

Hook Up Low Voltage Wiring (24 Volts)

Back to Step 8                  Continue To Step 10

Hook up Low Voltage Wires to Condensing Unit
  Hook up Two-Conductor, 18-Gauge wire (found in Supplies Package) to condensing unit. 
  1.  Run wires out hole in side of house.
  2.  Outside, pull wires through hole and run towards condensing unit. 
  3.  Run wires up through low-voltage electrical hole in front of condensing unit. 
  4.  Strip 1/2" of insulation from end of both wires. 
  5.  Use two blue wire nuts to connect the two incoming 24-volt wires with the 24-volt wires already attached to the condensing unit. 
  6.  Make sure all four wires are stripped 1/2". 
  7.  Secure wire nuts by squeezing on ends of wires. 
  8.  Replace access panel on condensing unit. 
(After your contractor solders your line set connections, replace the foam insulation that you had previously removed from suction line.  Use tie wraps to secure it.)
(Run 24-Volt wire along same line and secure with additional tie wraps.  Wait to do this until you can replace the insulation.)
 Run Low Voltage Wiring Along Ceiling to Furnace or Air Handler
  1.  Inside, run the 24-Volt wire alongside the line set and secure with plastic tie wraps. 
  2.  Make sure that the power to the furnace/air handler is turned OFF. 
  3.  Remove the access panel on the front of the furnace/air handler. 
  For a standard gas furnace, the control wiring area displays five or six terminals.  Terminals are labeled C, Y, Gc, Gh, R and W or C, Y, G, R and W.  Notice that two wires from your thermostat are already hooked up to the R and W terminals. 

4.  Trim the two 24-Volt wires so that they are long enough to reach the terminals. 
5.  Strip both wires back 1/2".
6.  Hook up either of the two wires to terminal C and tighten down with a screwdriver. 
7.  Hook up the other wire to terminal Y and tighten down with a screwdriver. 
(Some furnaces require you to make connections with wire nuts. In this case, you will connect the 24-Volt wires to the blue furnace wire and the yellow thermostat wire using wire nuts.  For more information on wiring for these, see our wiring diagrams.)


Next, you will hook up the thermostat to the condensing unit so that it can turn the air conditioning on and off.

You need a total of four wires to run from the thermostat to the furnace/air handler to make the air conditioning run.  The wire hooked to the R and W terminals should be four-conductor wire (meaning that two extra wires will be available to hook to two more terminals for air conditioning).  The two extra wires should be protruding from the wire casing.  If there are not two extra wires, you only have two-conductor wire and it must be replaced with four-conductor wire. 

  8.  Hook the extra green wire to the G or Gc terminal and the extra yellow wire to the Y terminal. 
  9.  Replace access panel on furnace or air handler. 
Run Wires from Furnace/Air Handler and Hook up to Thermostat
  10.  Remove the cover from your thermostat.  Make sure your thermostat has both heating and cooling capability.  Install a new thermostat if necessary.   

11.  Inside the thermostat, hook up the white wire to terminal W, the green wire to terminal G, the yellow wire to terminal Y, and the red wire to terminal R (if there are two R terminals, be sure to install a jumper). 

If this is not the lettering configuration in your thermostat, simply leave the wires hanging for final installation by your contractor. 

  12.  Replace your thermostat cover.

Back to Step 8                  Continue To Step 10

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