How To Test and Replace a Thermostat

Maintaining the thermostat on your home air-conditioning window unit is vital to keep the whole system working properly. It won't be a difficult or burdensome task if you folllow the guidelines mentioned below.

What You'll Need
You'll want to have these tools on hand to test or replace a thermostat:
  • Screwdriver
  • Volt-ohmmeter or multimeter
  • Replacement thermostat

Thermostat

The thermostat is located behind the control panel. Here's how to test and/or replace the thermostat:

Step 1: Remove grille and control panel from unit. Thermostat has special sensing bulb attached to it; this part extends from thermostat into evaporator coil area. Its role is to sense temperature, which is controlled by thermostat.

Step 2: Remove thermostat carefully because you must return sensing bulb to identical spot later. To make replacement easier, tag location of bulb before you remove thermostat.

Step 3: Check thermostat with VOM set to RX1 scale. Clip probes of tester to thermostat terminals, and turn temperature control dial to coldest setting. If meter reads zero, thermostat is functioning properly. If reading is higher than zero, replace thermostat with new one of same type. If thermostat is held to control panel or frame with screws, clips, or metal tabs, connect new thermostat the same way the old one was connected.

Note: If the thermostat has more than two lead wires connected to it (not counting the sensing bulb wire) do not try to test or replace it. Instead, call a professional service person.

The fan in your air conditioner also needs routine maintenance. Learn how to keep it running smoothly on the next page.

For more articles on home repair, check out the following links.

  • How To Repair Central Air Conditioners: If your system sends cool air to all parts of the house, you've got central air. Keep the system running cool.
  • Major Appliance Repair: If the a/c isn't the only thing in your house on the fritz, you can learn how to fix other machines in this article.
  • Small Appliance Repair: Once you've tackled the a/c, a toaster or blender seems like child's play. Find out how to fix them here.
  • Thermostat Maintenance: To make sure there's actually a problem with your a/c, you may want to check the thermostat, too. Learn how to calibrate a thermostat.