DIY Fixes Before Calling the Heating and Air Conditioning Service Man

PROBLEM
My heater/air conditioner will not turn on/I just came home and my house is hot/cold.

1. Check you thermostat. Does it need a new battery? Make sure it is set to cool / heat and the temperature is set lower / higher than the temperature of the house. Most of the newer t-stats have a lock out feature to prevent damage to the compressor. If you turn it off and on ( heat to cool or turn the temp up and down ) it will lock out for a preset time, usually 5 to 10 minutes. Some t-stats will flash "cool" on the display while locked out. It will stop flashing and the unit will run after the lock out time has expired.

2. Check the emergency switch. The indoor unit should have a switch, usually with a red switch plate, near the unit. It could be on the unit itself, on the wall next to it or near the stairs to the basement / attic. Some houses have more than one switch, so look around. Friends, family or the housekeeper could have turned it off accidentally especially when the unit is in a small laundry room. Put some tape on the switch to prevent this mistake.

3. Check the service door on the indoor unit. The door has a safety switch that will turn off the unit when the door is removed. Some units have the filter inside and the door might not have been replaced correctly. Sometimes the doors do not fit tight and could be bumped by the vacuum, kids or pets. An older unit might need a sheet metal screw to hold the door against the switch.

4. Check the fuse / circuit breaker in the electric panel. It should be a 15 amp breaker for the indoor unit. Some are 220 volts, but most are 110v. Turn it off and back on. Even the breaker looks like it is on, it might need to be reset.

5. Check your condensate pump ( if equipped ). Air conditioners and high efficiency heaters remove humidity from the air. The water condenses on the indoor coil, falls on to the drain pan and down the drain line, usually a 3/4 inch plastic pipe. It could gravity drain out of the house or have a small pump about the size of a shoebox. Some pumps have a float switch that can shut off the indoor and / or outdoor unit depending on how it was wired. The safety switch will turn off the A/C if the pump fails to prevent water damage to the house. All pumps will have a standard 110v cord that plugs into an outlet. If your pump has a safety switch it will have 2 extra wires about the size of a speaker wire. You can tap your pump because the float can stick. You can stick your finger into one of the holes to see if it's filled. You could pure water into the pump to see if it turns on and drains the sump. Cut the top off of a 2 liter soda bottle to make a funnel. The sump is bigger than it looks it could take a few glasses of water before it pumps. You can by-pass the safety switch to see if it is giving you a problem. The wires to the safety switch on most pumps are only a few inches long so the connection should be outside of the unit. The wires that come from inside the unit should be attached to the pump with wire nuts. Unscrew the nuts and twist all of the wires together. If the unit runs you need to replace the pump. You can get one at the local home store or plumbing supply.

6. Make sure you have fuel for the heater to burn. Check the tank if you have oil heat and remember the fuel gauge could lie. Make sure you have gas getting to the furnace if you have gas heat. You can light the stove or check the pilot light on the water heater to make sure the gas is not turned off to the house. The heater will have it's own gas valve near the heater. Make sure it is not turned off. If your unit has a pilot light, make sure it's light. Most gas heaters no longer have a standing pilot, they have electric ignition.

7. Check your air filter and vents. Reducing the air flow can cause the A/C to freeze up and your heater to overheat. Some people think they can save money by closing most of the vents in the house. This acts the same as a clogged filter. You can use the vents to make small adjustments for hot and cold areas, but must leave most of them open. If you must have furniture against a vent try to leave a couple inches of clearance. Do not run the unit without a filter.

Still not running?

There is one more thing you can do before calling the serviceman. Turn off your unit at the emergency switch or the breaker. You can damage the unit, so turn it off. Remove the thermostat from the wall.

For AC: Look for the wires marked R, G and Y. They are usually color coded, but not always so don't worry if your wires are different. R is 24v power and should be red. G turns on the indoor fan and should be green. Y turns on the outdoor unit and should be yellow. If your colors are different make a cheat sheet so you can put them back where they go. Twist all three wire together. Make sure they are not touching anything else and turn the unit back on.

For Heat: Find the wires marked R and W. They should be red for R and white for W. Twist they together and turn the unit back on.If your thermostat was bad the unit will run. If not you probably have a problem inside the unit and need to call someone.

A/C ONLY
The indoor unit is running, but not the outdoor unit is not.

There is not much to check at the homeowner level for this problem.

1.The outdoor usually unit is powered by 220v. If it is it will have a double pole circuit breaker. Turn it off and back on to reset the breaker.

2. Check the indoor condensate pump. If it has a safety switch it could be wired to turn off the outdoor unit, but leave the indoor unit running. ( see #5 above )

3. Most outdoor units have a service disconnect on or near them. Some disconnects have fuses inside. If you want to check the fuses you should have a fuse puller ( $15 at the home store ) a multimeter to check the old fuses ( $3 on sale at Harbor Freight or more from the home store ) Turn off the breaker for the outdoor unit. Make sure you have the right breaker, you don't want to be shocked. Open the disconnect box and pull out the disconnect. Some boxes have the fuses in the pull out. If not there should be a plastic cover inside the box. It's usually held in by a screw. Remove the cover and you should see the fuses, but remember not all disconnect boxes have fuses. Use the fuse puller to remove the fuses ( yes, I know you can pry them out with a screw driver or pliers, but I'm not recommending it ). Set the multimeter to Ohms, make sure the leads are in the proper spot on the meter. Touch the leads together and look at the screen for the reading it should be zero for zero resistance. If your meter has a tone function the tone should sound when the leads touch. Touch one lead to each end of the fuse. Push with some force and twist the point into the fuse to be sure you have a good connection, especially on old fuses that have oxidation. If the reading doesn't change the fuse is bad. If the reading goes to zero and the tone sounds the fuse is good. Check the other fuse because one bad fuse will stop the unit from running. If you find a bad fuse make sure you replace it with a slow blow or motor protection fuse. A standard fuse will not work. Replace the bad fuse, reassemble the disconnect box and turn on the breaker. The unit should run. A fuse can blow from age even though there is nothing wrong with the unit. If the fuse blows again there is probably an under laying problem. Make sure the cooling fan on the unit is running. The coil on the outdoor unit should be clean so air can blow through it. Make sure weeds or plants are not growing on the unit. There should be 12 inches of clearance for enough airflow. Grass clipping, dirt and dryer lint ( if the vent is close ) can be sucked into the coil and reduce the air flow causing the unit to run hot and blow fuses especially on a hot day. You might be able to clean it from the outside. Turn off the circuit breaker to the outdoor unit even if you blew another fuse because one fuse is probably still good and the unit is still getting 110 volts. Spray the coil with your garden hose. Start at the top and slowly work your way to the bottom. If the debris is not packed too tighly into the coil it will wash off.