Furnace and AC both not working: what they share

Why a furnace and AC can fail together

A furnace and AC both not working usually points to a part the two systems share. They run off the same thermostat, the same indoor blower, the same filter and the same ductwork. They also draw from the same electrical supply.

One weak link in that shared chain can stop heat and cooling at once. A single dead thermostat or a clogged filter can look like two broken machines.

Which shared parts can stop both systems?

Start with the control side. A thermostat with dead batteries or a wrong setting can leave both systems idle. A tripped breaker or a power outage does the same, because the blower and the controls need power in either mode. For electric service, Spanish Fork Power & Light provides electric service to homes and businesses in Spanish Fork. An outage question goes to that utility.

Next is airflow. The indoor blower pushes air through the filter and the ducts in both seasons. A very dirty filter, a blower that has stopped or ducts with closed or blocked vents can all choke the air. Weak airflow in winter can make a furnace shut itself off. In summer it can let ice build on the refrigerant lines.

For more on how this plays out in a single system, see the hub page on HVAC in Spanish Fork.

What can you safely check first?

These checks are safe for a homeowner and need no tools. Go in this order:

• Look at the thermostat. Check that it is on the right mode, that the setting makes sense, and that the batteries are fresh if it uses them.
• Check the air filter. If it is gray and packed with dust, swap it for a clean one that fits.
• Check the breaker panel. If a breaker has tripped, flip it fully off and back on a single time.
• Open the vents and returns. Make sure rugs, furniture and curtains are not blocking them.
• Look at the outdoor unit. Leaves, snow or stored items should not crowd the cabinet, so move them well back.

If a breaker trips again after you reset it, leave it alone. A repeat trip points to an electrical fault, and that is work for a licensed contractor.

What should stay with a licensed contractor?

Some jobs are not for a homeowner. Handling refrigerant, working on live electrical parts or wiring, servicing the gas side of a furnace, and opening any sealed component all belong to a licensed contractor. A licensed contractor checks the wiring, tests the controls and works on the gas burner and its valves.

Two safety rules come before any checking. If you smell gas, leave the house, then call the gas utility from outside. If a carbon monoxide alarm sounds, get everyone out and call emergency services.

Do not relight a furnace that keeps dropping out, and do not bypass a safety switch to get the blower going. Those switches shut a system down for a reason.

How do Spanish Fork seasons strain both systems?

One set of equipment handles a wide swing. The NOAA weather station near Spanish Fork averages 5,415 heating degree days a year, which is a measure of how much heating the cold months call for. The same station averages 1,013 cooling degree days a year, the matching measure for cooling.

On the cold side, the station averages 118 days a year with a low of 32°F or below. On the hot side, it averages 60 days a year with a high of 90°F or more. A shared blower and filter work hard in both stretches.

The coldest night in that station's record fell to -20°F, on 1989-02-07. Equipment that sat idle between seasons can fail the first time it is asked to run hard. The spring and fall HVAC checklist covers checks that help catch this early.

If the fix turns out to be a replacement, ask about permits. Spanish Fork City lists HVAC replacements among the common projects covered by a residential permit.

When is it time to call about HVAC availability?

Call when the simple checks do not bring either system back, or when a breaker keeps tripping. Call too if you hear a new noise from the blower or see ice or water at the indoor unit.

Where a contractor is available, the line connects the call to a licensed, insured contractor. That contractor then confirms availability and fees. For more on the service itself, read about HVAC in Spanish Fork.