Tips & Tools

Home Troubleshooting Guide For Your Heating and Air Conditioning System

Courtesy of: United Heating & Air Conditioning

We all may experience problems with our heating/air conditioning system that leave us less-than-comfortable. Often, the cause is simple; a switch position or filter change. This document lists some common residential problems and suggests thing you can try to solve those problems without needing to call a serviceman. Of course, annual checkups and servicing by a qualified technician do much to prevent problems and prolong the life of your heating and air conditioning systems.

We do recommend this, but in the meantime, follow these suggestions in the order listed below to get the best from your system.

Caution: Do Not remove protective covers from equipment. Injury or death from electric shock may occur.


System will not come on at all.

  1. Check your thermostat. Make sure it is switched to “cool,” the temperature is set to the temperature you want, and the fan switch is set to “Auto.”
  2. Reset electrical circuit breakers, a.) on or around the indoor unit, or possibly a wall type switch if you have a gas heater; or , b.) in the home’s main electrical panel (will be listed as A/C or Heater.)
  3. If you have a gas furnace, check the doors that provide access to the filter, If they are misaligned or not secure, the safety switch will not make contact. Install the door properly and securely.

System is running, but not cooling

  1. Check your thermostat. Make sure the fan switch is set to “Auto” and the temperature is set below the current thermometer reading.
  2. Check the circuit breaker/fuse box outside, connected by conduit to the outside portion of your air conditioning system (a large, vented metal structure roughly 3’ cubed, with a fan inside. The fan will be operating when system is cooling.) Reset if needed.
  3. Check your filter, If the filter is clogged, air will not flow, resulting in a frozen-over air evaporator coil inside. Replace our filer often. We recommend filter change at least bimonthly.

System is running continuously, getting colder and will not shut off.

  1. Check your thermostat to be sure it is on the desired temperature. If so, the contacts may be stuck, or some wires may be crossed.

Indoor fan will not shut off. System cooling ok

  1. Make sure the “FAN ON-AUTO-OFF” switch is in the ‘AUTO” position.

Water is leaking around equipment inside home

  1. Check filter. If clogged, it could cause ice to form in the system, which will then melt in your home. Leave the system off three to six hours to allow all the ice to melt after changing the filter.
  2. Make sure no return air vents into the system are blocked. This could also reduce airflow enough to cause icing-up.
  3. Check the drain to ensure it is not clogged.


Uneven temperatures in different rooms of the house

Although it is common for here to be as much as three degrees difference between rooms, there may be a problem you can fix.

  1. Check for open outside doors or windows.
  2. Check inside doors your close to ensure there’s a gap for air to return to our system when operating or that return-air ducts are open.
  3. Adjust the damper levers (they will open and close to allow more or less air into a room) located on each air outlet grill.

Rattling noise or whistling in one or more outlet grills

Move the damper lever on the grill just slightly. This may tighten up loose louvers so they will not rattle. Whistling is often caused by the damper lever being closed to far. Open it slightly.

Abnormally high electric bills

  1. Check filter for cleanliness. Replace if dirty. Clogged filters cause your system to work much harder and run longer.
  2. Check home for leaks, including doors and window, or poor weather stripping.
  3. Adjust window shades and blinds to reduce direct sunlight.
  4. Adjust thermostat to a slightly higher setting.
  5. Be sure the cause is not just unseasonably warm weather.


Furnace will not come on

  1. Check thermostat. Be sure it is switched to the “Heat” position, and the fan switch is set to “Auto.”
  2. If our system has a pilot light (most older systems do) be sure it is lit.
  3. Look inside the cabinet where the furnace is located for a switch that looks like a wall switch. Be sure it is in the ON position.
  4. Check electrical circuit breakers at the system or at the main panel. If unsure of whether the breaker is tripped or not, switch it off and then back on to be sure.
  5. Check the doors where you replace the filters on the unit. A safety switch will not allow the system to operate if doors are not secure.

Furnace comes on, but shuts down before reaching desired temperature

  1. Check filters for cleanliness.
  2. Check for blockage of return air vents, (especially at the unit.)
  3. If the house is below 64F, the system may cycle on-and-off until the temperature rises a couple of degrees, and then will operate normally.

System is running, but no heat is produced

  1. Check thermostat settings. Be sure fan switch positions is “AUTO,” the selector is set to “HEAT,” and the temperature is set above the current room temperature.
  2. Check filter and for obstructions around return-air grills.
  3. Check pilot light if you have one. Refer to owner’s manual for lighting instructions.

System produces too much heat, and will not shut off

  1. Check thermostat t ensure it has not been turned up too high.
  2. If thermostat is very old, it may need to be replaced. If it is new, it may be wired improperly, or it may be incompatible with your system.


System will not come on

  1. Check thermostat. Be sure it is switched to the “HEAT” position, and the fan switch is set to “AUTO.”
  2. Check electrical circuit breakers at the system or at the main panel. If unsure of whether the breaker is tripped or not, switch if off and then back on to be sure.
  3. Check the doors where you replace the filters on the unit. A safety switch will not allow the system to operate if doors are not secure.

Air handler is running, but not heating

NOTE: The warming air from a heat pump does not feel as warm as the air from a gas or oil furnace. Wait a few minutes to see if the temperature in the room is actually rising to the desired temperature.

  1. Check thermostat settings. Be sure fan switch position is “AUTO,” the selector is set to “HEAT,” and the desired temperature is set.
  2. Check the outdoor portion of the unit to make sure it is running. If not, check the “disconnect” circuit breaker in the box on the wall near the unit.
  3. Press the Reset button on the unit inside “button is usually located near where the refrigerant line enters the unit.”
  4. If you are still not getting enough war air, set thermostat to “EMERGENCY HEAT.” Call a qualified service technician.

Outdoor unit is steaming (may appear to be smoking)

NOTE: Unit may be defrosting itself. This is normal. Recheck after about 15 minutes. If compressor and fan operate normally, there is no problem.

  1. If you are unsure, smell the “smoke.”
  2. If it smells acrid, shut the system down and call a technician.

“Auxiliary Heat” light comes on often, especially in cold weather

NOTES: This is normal in very cold weather, especially if the heat pump installed is not of sufficient size to meet the needs of your home. It will also come on any time the thermostat is set three or more degrees above the temperature in the house.

“Reset” button trips frequently

  1. Check filter for cleanliness
  2. Ensure return-air grills and openings are not blocked

Check the outside unit to ensure trash or leaves are not blocking the proper ooperations and airflow of he coils.

We hope this information helps you keep your heat and air conditioning system working properly. If after trying the steps listed you still are not able to get your system functioning as needed, we suggest you call a professional service technician.

Our own technicians are some of the most highly trained professionals in the business. We are available 24 hours, seven days a week to keep you comfortable and highly satisfied with your heating and air conditioning system.