HVAC guide from iLikeTo Fix

Heating & cooling problems and what to do first

AC not cooling, furnace not firing, uneven rooms, humidity and ductwork. Find the symptom you are seeing, run the checks a technician would start with, and know what a fair repair looks like before you call.

41 heating and cooling problems, each named by the symptom you see

Sorted by the decade your house was built

Checks to run yourself and what fair repair costs look like

Find your problem Checks to run first

41 problemsEvery heating and cooling problem we cover, on this page

4 house erasPre-1940, 1940–80, 1980–2000 and since 2000

Checks firstWhat to rule out before anyone comes out

Fair costsWhat the work costs, and what not to pay for

1Find your problem

Start with the decade your house was built. The same symptom has different causes in a 1930s house and a 2010s one, so each era lists the heating and cooling problems that concentrate there.

Before about 1940 1940 to 1980 1980 to 2000 Since 2000 Any age

Homes built before about 1940

Galvanized supply, cast iron drains, cloth-wrapped wiring, ungrounded circuits.

All heating and cooling in homes built before about 1940

Ductwork threaded through a house built for floor grates One central return for the whole house Water heater vents into the chimney and the furnace no longer does Silver-wrapped tape on old duct joints Additions still on window units Uninsulated walls and an oversized condenser Furnace runs but the house never warms evenly Electrical panel cannot support a modern condenser Filter slot is a gap behind a grille

Homes built roughly 1940 to 1980

Copper supply, aging cast iron stacks, 60 to 100 amp panels, first-generation central air.

All heating and cooling in homes built 1940 to 1980

R-22 system leaking refrigerant Rust or soot streaks at the furnace heat exchanger Ducts in an unconditioned attic Thermostat has only four wires Condenser pad has sunk and the unit leans System cools but the house stays humid Evaporator coil freezing over Only some rooms cool, and always the same ones Blower runs constantly and never satisfies

Homes built roughly 1980 to 2000

Polybutylene and aluminum wiring, 150 amp panels, R-22 systems.

All heating and cooling in homes built 1980 to 2000

SEER 10 system still running at thirty years Flex duct crushed or kinked in the attic Water on the floor near the air handler Cooling drops off on the hottest days only One zone stuck hot or cold Squeal or grind from the air handler Refrigerant line insulation crumbling Outdoor unit caked in cottonwood and red dust Thermostat set to 72 and the house reads 78

Homes built since 2000

PEX on slab, 200 amp service, builder-grade equipment failing street by street.

All heating and cooling in homes built since 2000

Whole street replacing systems the same year Upstairs runs hot no matter the setting Control board fault on a communicating system Smart thermostat installed and the heat now runs oddly Condensate pump buzzing or backing up White PVC vent pipes outside stained or dripping House feels stuffy in a new build Fifteen degree difference between floors Loud startup thump from the outdoor unit

Any age of home

Problems that turn up whatever the decade.

Furnace ignites, runs a minute, shuts off Gas smell near the furnace Heat pump runs constantly below freezing Outdoor unit steaming in winter Dual fuel system switching at the wrong temperature

2Checks to run first

Work through these in order before you book anyone. They cost little or nothing and often find the answer.

Check the thermostatRight mode, a setpoint a few degrees past room temperature, fresh batteries. A surprising number of calls end here.
Look at the filterA clogged filter starves the system of air, freezes coils and trips safety switches. Replace it if you cannot see light through it.
Check power to both unitsThe breaker for the furnace or air handler, the switch beside it, and the disconnect next to the outdoor unit.
Clear the outdoor unit and the drainCut back plants, rinse off cottonwood and debris, and check the condensate line and float switch if the system shut itself off.

3What heating and cooling work costs

The short answerAccess drives the number more than materials do. Every problem page gives a range for judging a quote, and the cost guide lists the heating and cooling work you should not be paying for at all.

Read HVAC cost: what to expect and what to skip before you compare quotes. A quote that cannot explain what it includes, or that fixes the visible symptom while leaving the cause behind, is the one to question.

4When to call an HVAC technician

Read the page for your problem first. It says whether this is a job for a pro, and what a fair price looks like before you make the call.

Speak to a local HVAC technician

Calls connect to an independent local contractor. How this works.

5Questions

Why is my AC running but not cooling?

Start with the filter, the outdoor unit and the thermostat. If air flows but is not cold, the coil may be frozen or the system low on refrigerant, which needs a technician.

How long should a furnace or AC last?

Many systems run fifteen to twenty years. Age alone is not a reason to replace one; repeated failures, rising bills and an obsolete refrigerant are.

Repair or replace?

Weigh the repair against the system's age and condition. A large repair on an old system using phased-out R-22 refrigerant usually points to replacement; a capacitor or contactor on a ten-year-old system does not.

Why is one room always hotter or colder?

Usually duct layout, a single central return, leaky or crushed ducts, or a room the system was never sized for, rather than a broken unit.

Written by Jaylan Jones. iLikeTo Fix earns a referral fee when a call connects to a contractor. See our business-model disclosure.

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