AC Compressor Not Running? Portland Troubleshooting Guide
When your outdoor unit refuses to start, indoor comfort disappears fast. Use this Portland-focused guide to identify the top reasons compressors stop running, what you can check safely, the typical repair costs, and when to call Efficiency Heating & Cooling for rapid service.
Serving Portland, Beaverton, Tigard, Happy Valley, and surrounding communities since 2008.
Owner & Lead HVAC Technician
Quick Answer
The Compressor Stopped — Now What?
If your AC compressor is not running while the indoor blower operates, the most common culprits are failed capacitors, pitted contactors, tripped breakers, or low refrigerant. Repairs range from $150 for electrical parts to $2,500 for full compressor replacement. Follow the checklist below and call us if electrical components are involved — they require licensed handling.
Set the thermostat to COOL and at least 3°F below current room temperature.
Check the main electrical panel and outdoor disconnect for a tripped breaker.
Clear debris, leaves, and cottonwood fluff from around the outdoor condensing unit.
Listen for humming, clicking, or complete silence at the outdoor unit to narrow the issue.
Gently rinse condenser coils with a garden hose to remove pollen and dirt (power OFF first).
Stop DIY and call a licensed HVAC pro for any electrical or refrigerant work.
Why Compressors Fail in the Portland Metro Area
Portland’s moderate climate means AC systems rest for months, then leap into action when unexpected heat waves roll through. Long idle periods allow moisture-driven corrosion and rodent intrusion, while sudden surges in usage stress electrical components that have been sitting dormant. Add in cottonwood pollen clogging coils, and it is no surprise the compressor is often the first part to complain. The good news? Most failures relate to inexpensive electrical parts that can be replaced quickly if caught early.
Start by identifying the sound or lack thereof at the outdoor unit. Humming generally points to a capacitor or seized compressor. Clicking without start-up screams contactor trouble. Tripped breakers indicate deeper electrical problems or mechanical lockups. Use the following deep-dive on the 10 leading causes to pinpoint your next steps.
Failed Start or Run Capacitor (40% of service calls)
Capacitors store and release a jolt of electricity that helps the compressor start and continue running. Portland summers are generally mild, but when the temperature spikes into the 90s or we experience multiday heat waves, capacitors endure repeated strain. Age, power surges, and prolonged inactivity between seasons cause the dielectric material to degrade.
- •Symptoms: Outdoor unit hums but fan and compressor do not spin; visible bulging or leaking oil on capacitor casing.
- •Typical lifespan: 7-12 years, shorter if the system sits idle in damp coastal air or is oversized and short cycles.
- •Repair cost: $150-$400 including diagnosis, OEM capacitor, and bench testing of associated components.
- •DIY risk: Even when power is disconnected capacitors can hold a 240V charge that can seriously injure; replacement is always professional-only.
- •Portland tip: Install a whole-home surge protector to shield capacitors and boards from PGE voltage fluctuations.
Pitted or Burned Contactor
The contactor is the heavy-duty electrical relay that feeds power to the compressor and fan motor. Every time the thermostat calls for cooling, the contactor closes. Over time, arcing pits the contacts and prevents a solid electrical connection. High humidity levels east of the Willamette accelerate corrosion on unprotected relays.
- •Symptoms: Rapid clicking when the thermostat calls for cooling, outdoor fan may run without compressor.
- •Repair cost: $150-$350 depending on single- or two-pole contactor and accessibility.
- •Professional only: Requires electrical testing and safe handling of live wires at the disconnect.
- •Prevention: Annual AC maintenance includes contactor inspection and tightening low-voltage wiring loosened by vibration.
Tripped Circuit Breaker or Blown Fuse
A simple breaker trip can stop the compressor from running while indoor components seem normal. Breakers trip due to lightning, brownouts, shorted wiring, or compressor over-amp conditions. Many Portland homes also have cartridge fuses in the outdoor disconnect that can blow after a heavy rainstorm.
- •DIY step: Reset the breaker once; if it immediately trips again, leave it OFF and call a professional.
- •Check both the main panel and the outdoor fused disconnect near the condenser.
- •If breakers trip repeatedly it may signal a seized compressor, weak capacitor, or failing motor drawing excess amps.
- •Cost: Free if a one-off trip; $250-$600 if wiring or breaker requires replacement.
Thermostat or Low-Voltage Control Issues
Misconfigured thermostats are a surprisingly common culprit after winter heating season. Batteries die, mode is left on HEAT or OFF, or advanced thermostats suffer software glitches after Wi-Fi updates.
- •Check thermostat mode, set point, fan setting, and batteries before diving into mechanical issues.
- •Loose thermostat wiring (especially in older Portland homes with plaster walls) interrupts the Y signal to the condenser.
- •Cost: $0 for adjustments, $200-$350 for thermostat replacement, $150-$300 for low-voltage wiring repairs.
- •Pro tip: Use remote sensors or relocate thermostats away from west-facing windows to prevent false readings during late sunsets.
Low Refrigerant Charge or Active Leak
Modern systems have pressure switches that cut power to the compressor when refrigerant levels drop too low. This prevents overheating but leaves homeowners with a warm house. R-410A leaks most frequently at flare fittings or evaporator coils in attics and crawlspaces.
- •Symptoms: Ice buildup on refrigerant lines, bubbling or hissing noises, reduced airflow, high indoor humidity.
- •Repair cost: $200-$1,500 depending on leak location, access, and recharge volume.
- •Environmental note: Refrigerant handling requires EPA certification; do not attempt to top off yourself.
- •Portland insight: Homes with flexible ducts and vapor barriers often hide slow leaks that only reveal themselves during the first big June heat wave.
Dirty or Blocked Condenser Coils
Portland’s cottonwood season (May–June) coats outdoor coils with fluffy seeds that trap dirt and grass clippings. A dirty coil overheats the compressor, triggering the high-pressure safety switch. Coastal moisture further traps debris in coil fins.
- •DIY: With power off, spray coils from the inside out using a hose with gentle pressure — never a pressure washer.
- •Professional cleaning: $100-$200 with coil-safe cleaners and fin straightening.
- •Preventive maintenance: Trim vegetation to maintain a two-foot clearance and schedule spring tune-ups before pollen hits.
High-Pressure or Low-Pressure Switch Trips
Pressure switches monitor refrigerant conditions. If head pressure spikes or suction pressure plummets, the switch opens and stops the compressor to prevent catastrophic failure.
- •High-pressure triggers: Blocked coils, non-condensables in the system, or excessive refrigerant charge.
- •Low-pressure triggers: Refrigerant leaks, iced indoor coils, or severe airflow restrictions.
- •These switches typically auto-reset but repeated trips signal an underlying fault that must be diagnosed.
Faulty Wiring or Rodent Damage
Portland’s love of crawlspace storage inadvertently attracts rodents. Chewed low-voltage wires or corroded splices interrupt power to the compressor. Moisture intrusion in conduits also causes corrosion at wire nuts.
- •Look for visible chew marks, frayed thermostat wire insulation, or burnt connections inside the service panel.
- •Repairs run $200-$600, often combined with installing conduit or rodent-proof coverings.
- •Include wiring inspection in annual maintenance after heavy winter rains.
Seized or Locked Compressor
A compressor that has mechanically seized will pull locked-rotor amps and trip the breaker immediately. Causes include lack of lubrication, acid buildup from previous burnout, or debris from manufacturing defects.
- •Diagnostics include megohm tests, amp draw measurements, and oil sampling.
- •If seized, repair options are limited to compressor replacement ($1,500-$2,500) or full system replacement.
- •In Portland’s climate, a well-maintained compressor should last 18–22 years; failure earlier than that often indicates systemic issues like duct restrictions or improper installation.
Control Board or Hard Start Kit Failure
Variable-speed systems and heat pumps often rely on sophisticated control boards to engage the compressor. Boards damaged by voltage spikes or moisture will fail to deliver the start signal.
- •Replacement control boards cost $300-$900 plus labor.
- •Hard-start kits added for older compressors sometimes fail and need replacement to provide the starting torque.
- •Install surge protection and ensure proper equipment grounding to extend board life.
Repair Cost Breakdown
Understanding typical price ranges helps you budget — and spot too-good-to-be-true offers. We provide upfront, flat-rate quotes before any work begins. Emergency service is available during heat waves with no surprise after-hours fees for maintenance plan members.
Prices reflect typical Portland metro jobs in 2026 and include parts, labor, testing, and 1-year workmanship warranty.
When It Is Time to Replace Instead of Repair
Compressors rarely fail twice without a systemic reason. If your system is aging or uses R-22 refrigerant, investing in a new high-efficiency AC may save thousands over the next decade. We help you weigh the options with honest, pressure-free advice.
Replace Compressor If:
- •System is < 8 years old and parts are under warranty
- •No history of major electrical failures
- •Ductwork is newer and properly sized
- •Repair cost is < 40% of new system cost
Replace Entire AC If:
- •AC is 12+ years old or uses phased-out R-22 refrigerant
- •Multiple components have failed in the last 24 months
- •Energy bills are climbing despite maintenance
- •You want quieter, more efficient variable-speed technology
We provide side-by-side estimates so you can compare the 5-year cost of each option, including rebates and energy savings.
Portland AC Compressor Repair FAQs
Need Fast AC Compressor Repair in Portland?
Our NATE-certified technicians arrive with fully stocked trucks, diagnose problems on the first visit, and back every repair with a satisfaction guarantee. Don’t wait for the next heat wave to strike — restore cooling comfort today.