Air Conditioning Not Turning On Greater Vancouver

An air conditioner that does not respond when the thermostat calls for cooling has a power, control, or safety fault — most of which can be narrowed down with a few quick checks.

What This Means

Both the indoor air handler and the outdoor condensing unit must have electrical power and receive a thermostat signal for the system to start. A fault at either unit, or in the control wiring, prevents startup.

Common Causes

• Circuit breaker for the outdoor unit tripped
• Disconnect switch at the outdoor unit open or failed
• Thermostat batteries dead or thermostat set to heat or off
• Float switch tripped — condensate drain backed up and shut the system off as a safety measure
• Contactor in the outdoor unit failed open
• Compressor thermal overload tripped from overheating

What Homeowners Can Check Safely

• Check both circuit breakers for the AC (indoor air handler circuit and outdoor unit circuit)
• Check the outdoor disconnect switch — a small box near the outdoor unit should have the disconnect in the ON position
• Replace thermostat batteries if the thermostat display is dim or blank
• Check the condensate drain for backup — if the primary drain is blocked, the float switch may have shut the system off

When to Call a Licensed Technician

Air conditioning and mini-split systems contain refrigerant under pressure and electrical components at line voltage. Do not open refrigerant circuits, attempt to recharge the system, or bypass safety controls — these require a certified technician.

• Contactor testing and replacement
• Float switch testing and drain clearing
• Compressor thermal overload reset and root cause diagnosis
• Thermostat signal wire testing

Frequently Asked Questions

Why did my AC circuit breaker trip?

An AC circuit breaker trips when the unit draws more current than the breaker rating. Common causes: a failed start capacitor (compressor struggles to start and draws excess current), a compressor winding fault, or a wiring problem. Reset the breaker once and observe — if it trips again promptly, the underlying cause must be diagnosed before further operation.

My AC does not come on but the thermostat shows it should be cooling. What next?

Start at the outdoor unit: confirm the disconnect switch is on and the circuit breaker has not tripped. Then look for a contactor — a relay in the electrical compartment of the outdoor unit that the thermostat controls. If 24V is present at the contactor coil but the contacts are not closing, the contactor has failed.

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