A wall-mounted heat pump that refuses to start can cause concern—especially on the coldest or hottest days of the year. This guide, written by AirGreen, expert in HVAC installation, maintenance and repair in Montreal, Laval, Longueuil, North Shore and South Shore, provides a clear, quick and structured roadmap to diagnose and efficiently resolve startup issues with your wall unit.
Understanding possible causes of startup failure
Startup issues with a wall-mounted heat pump can stem from several sources. Before calling a technician, there are a few things you can check on your own.
1. Check the power supply
Many failures simply come down to a power issue:
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Has the breaker tripped? Check your electrical panel and reset it.
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Has the fuse dedicated to your wall-mounted air conditioner blown?
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Is the wall outlet functional? Plug in another device to test it.
At AirGreen, we’ve found that 25% of service calls related to startup failure are caused by power interruptions, often due to overload or faulty electrical connection.
2. The remote control or control panel
Sometimes a simple dead battery in the remote can prevent the unit from responding:
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Replace the batteries, even if the screen still lights up.
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Make sure you're not in "Timer" or "Sleep" mode.
Our technicians often respond to calls in Montreal and Longueuil, where the only issue was an incorrectly configured remote.
3. Wall-mounted or integrated thermostat
If your unit is connected to a smart wall thermostat, verify the following:
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Is the thermostat powered and functional?
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Is the set temperature appropriate based on the current room temperature?
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Is the selected mode set to "Heating" or "Cooling," depending on the season?
One client in Laval, using a Fujitsu KZAH R-32 heat pump, thought their unit was broken. Our team simply reconfigured the smart thermostat, which was out of sync with the pump.
Troubleshooting steps you can do yourself
We recommend that owners of wall-mounted heat pumps follow these steps before scheduling a technician visit.
Step 1: Full unit restart
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Turn off the power at the breaker.
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Wait 5 minutes (this gives internal capacitors time to reset).
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Turn the power back on and wait for the system to restart.
Step 2: Clean the filters
Clogged filters can lead to startup blockage or immediate shutdown:
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Remove and wash the air filters.
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Allow them to dry completely before reinstalling.
During a recent job in Brossard, a customer with a Gree Extreme 18,000 BTU heat pump had skipped maintenance. A simple filter cleaning was enough to fix the issue.
Step 3: Check for blocked vents or frost
An outdoor unit that’s blocked or frozen can prevent startup:
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Make sure the outdoor unit is clear of obstructions (snow, leaves, ice).
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If automatic defrost isn’t activating, it could be a faulty control board.
Situations that require professional help
Some scenarios require a diagnosis by HVAC professionals:
Electronic control board failure
Printed circuit boards or control modules can fail. At AirGreen, we recently replaced the board of a Sharp ZU1 24,000 BTU wall-mounted heat pump in Pierrefonds, which was no longer responding to any commands.
Fan motor or compressor failure
If you hear a click but nothing else happens, it’s possible the fan motor or compressor is stuck or defective.
Faulty sensors
Temperature, pressure or flow sensors can block startup if readings are inconsistent. This is more common during extreme cold on the North and South Shores.
AirGreen’s approach to repairs
At AirGreen, we take a rigorous and personalized approach to every service call:
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On-site diagnostics by certified technicians.
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Use of genuine replacement parts (Fujitsu, Gree, Sharp, Tosot, Bosch, etc.).
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Programming optimization to prevent recurrence.
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Customized advice on maintenance and usage based on your model and environment.
In a recent intervention in Sainte-Julie, a Gree Sapphire 18,000 BTU wall-mounted heat pump had intermittent startup issues. After diagnosis, we replaced a faulty defrost sensor and reprogrammed the cycles, restoring optimal performance.
Practical tips to prevent future failures
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Service your heat pump twice a year, ideally before winter and summer.
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Protect the outdoor unit from harsh weather with a well-designed cover.
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Avoid power surges with a dedicated electrical protection system.
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Watch for warning signs (flashing lights, unusual noises, reduced performance).
When should you consider a full replacement?
If your wall-mounted heat pump:
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Is more than 10–12 years old,
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Requires frequent repairs,
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Consumes high energy despite regular maintenance,
… it might be time to consider replacing it with a more efficient model, such as the FUJITSU KZAH R-32, GREE SAPPHIRE, or Sharp ZU1—all available through AirGreen and eligible for Hydro-Québec LogisVert grants of up to $2,172.
Trust AirGreen
For years, we've been serving clients across Montreal, Laval, Longueuil, North Shore and South Shore to ensure their long-lasting comfort. Whether you need a quick repair, a full installation or preventive maintenance, our team is committed to delivering professional, efficient and human-focused service.
Your wall-mounted heat pump won’t start? Contact AirGreen now for reliable diagnostics and fast repairs.