Before You Call Anyone
Check Your Thermostat Settings
Set your thermostat at least 5 degrees below room temperature and confirm it reads “Cool,” not “Fan Only” or “Heat.”
A thermostat stuck on fan mode circulates air without triggering the compressor. No compressor = no cold air.
Inspect Your Air Filter
Pull it out. If it looks like a gray wool blanket, that’s your problem.
A clogged filter chokes airflow, causes the evaporator coil to ice over, and shuts down your system’s ability to cool. You’ll need to replace it.
Trane and Carrier both recommend checking filters monthly during peak cooling season.
Check for a Tripped Breaker
Your AC uses two breakers:
- One for the air handler inside
- One for the condenser outside
Both need to be on.
A tripped breaker means the compressor isn’t running even though the fan is.
Key Takeaway: A dirty filter is the number one preventable cause of AC failures. It’s a $10 fix a lot of people miss.
Common AC Problems That Require a Technician
If you’ve cleared the basics above and you’re still sweating, one of these is the likely culprit.
Frozen Evaporator Coil
When airflow is restricted for too long, ice builds up on the indoor coil.
You’ll often see frost on the copper refrigerant line near your air handler.
What to do:
- Switch the system to “Fan Only”
- Let it run for 2–3 hours
- Restart the system
If it freezes again, you have a bigger issue that’ll need a hvac technician to solve.
Low Refrigerant
Refrigerant doesn’t deplete on its own. If your system is low, there’s a leak.
Common signs include:
- Frost on the copper refrigerant line
- A faint hissing sound near the outdoor unit
- The system running constantly without reaching the thermostat setting
Dirty Condenser Coil
The outdoor unit removes heat from your home and releases it outside.
Grass clippings, cottonwood fluff, and dirt clog condenser coil fins, especially around Missoula and western MT during late spring.
When the condenser can’t release heat effectively, your AC may run continuously while blowing warm air.
You can gently rinse the unit with a garden hose, but heavily impacted coils usually require professional cleaning.
Failed Capacitor or Compressor
If the outdoor unit hums but the fan isn’t spinning, the run capacitor is often the culprit.
Capacitors are relatively inexpensive parts but should be replaced by an hvac technician.
A failed compressor is the worst-case scenario and one of the more expensive AC repairs, often costing between $1,500 and $2,500 depending on the system.
Why Missoula Homes Are Particularly Vulnerable to A/C Issues
Most homes in the South Hills, Miller Creek, Linda Vista, etc weren’t originally designed with aggressive air conditioning in mind.
Our temperature swings mean systems often sit dormant for months before being pushed hard during June, July, and August.
Extended inactivity can lead to:
- Drying seals
- Weakening capacitors
- Clogged condensate drain lines
Garden City, Air Quality, and Temp Rite all serve the Missoula and greater area but don’t outshine Right Now.
If you need same day service, clear, flat rate pricing, and a licensed technician, Right Now Plumbing and Heating is the call Missoulians and western Montanans make first.
“Joe and his crew onsite and in office go above and beyond. They are prompt, courteous, and very knowledgeable. Highly recommend Right Now Plumbing and Heating.”
— Verified Google Review
Is It Worth Repairing or Time to Replace?
If your system is over 15 years old and the compressor or refrigerant circuit has failed, replacement often makes more financial sense than repair.
Modern Carrier and Trane systems are significantly more efficient than units manufactured before 2010.
Frequently Asked Questions
Why is my AC running but not cooling the house?
The most common reasons are a dirty air filter, low refrigerant due to a leak, or a frozen evaporator coil. Start by replacing the filter and verifying thermostat settings before calling an hvac company.
How do I know if my AC is low on refrigerant?
Look for:
- Frost on the copper line near the air handler
- A faint hissing sound near the outdoor unit
- A system that runs continuously without reaching the desired temperature
Can I recharge my own AC refrigerant?
No. Refrigerant handling requires EPA 608 certification in Montana. Attempting to recharge it yourself is illegal and won’t address the underlying leak.
How long does it take for a frozen evaporator coil to thaw?
Switch the thermostat to “Fan Only” mode and allow 2–3 hours for thawing.
Do not run the compressor while the coil is frozen, as this can cause additional damage.
What does a bad capacitor sound like?
A humming or clicking sound from the outdoor unit without the fan spinning is a classic sign of a failed capacitor.
The unit is attempting to start but doesn’t have the electrical boost required.
How often should I change my AC filter in Montana?
Every 30–90 days during cooling season.
Homes near cottonwood-heavy areas would benefit from monthly filter changes.
What’s the lifespan of a central AC system?
Most central air conditioning systems last between 15 and 25 years with proper maintenance.
Routine service tends to push systems toward the upper end of that range.
When should I replace instead of repair?
If your unit is over 15 years old and facing a compressor failure or refrigerant circuit issue, replacement often provides a lower total cost over the next three to five years.
Written by the owner of Right Now Plumbing and Heating in Missoula, MT.