Why Your Wall-Mounted Heat Pump Seems to Blow Only Cold Air in Heating Mode (Urgent Fix)

When your heat pump blows cold air in heating mode: a frustrating situation, but often preventable

At AirGreen, every fall and winter we receive a growing number of emergency calls from homeowners in Montreal, Laval, Longueuil, the North Shore, and the South Shore, reporting a troubling issue: their wall-mounted heat pump is only blowing cold air when set to heating mode.

Although this issue is common, it can stem from multiple technical causes, ranging from a simple lack of maintenance to more complex failures related to installation or the compressor. In this article, we walk you through the most frequent causes, immediate solutions to consider, and best practices to follow to quickly restore thermal comfort in your home.

First check: is the mode properly set to “heating”?

It may sound obvious, but many of the calls we receive are simply due to an incorrect remote setting. Make sure the mode is set to “HEAT” or “CHAUFFAGE”, and not to “COOL” or “AUTO”.

Common confusion to watch for:

• The “AUTO” mode can switch between cooling and heating in erratic ways

• The fan may run without the compressor, giving the impression cold air is blowing

Is the outdoor temperature too low for your model?

Some entry-level wall-mounted heat pumps aren’t built to maintain a comfortable indoor temperature below -10°C to -15°C. In those cases, the fan may still blow air, but it's not actually heated.

At AirGreen, we install Energy Star certified models tested to operate down to -25°C or even -30°C, such as:

• Gree Sapphire

• Sharp ZU1

• Fujitsu KZAH

• Bosch Climate 5000 R-32

If your heat pump isn’t in this high-performance range, it may simply lack the capacity needed in extreme cold.

Defrost issue: is your outdoor unit frozen?

As the temperature drops, moisture in the air can freeze on the outdoor unit, blocking heat transfer. That’s why all heat pumps include an automatic defrost mode, which should activate at regular intervals.

Signs your system is frozen:

• The outdoor unit is covered in frost or ice

• A “hollow blowing” sound is heard indoors

• The air is warm at first, then turns cold

AirGreen solutions:

• Check the defrost cycles

• Professionally clean the outdoor unit

• Adjust firmware settings on select Fujitsu or Gree models to improve defrost logic

Has yearly maintenance been done?

Dust, dirt, or mold buildup on the evaporator or condenser can significantly impact overall performance. A neglected system may blow cold air in heating mode simply because it can no longer properly absorb or transfer heat.

At AirGreen, a full maintenance includes:

• Cleaning the evaporator and indoor blower wheel

• Checking refrigerant pressure

• Defrosting and cleaning the outdoor unit

• Testing the temperature sensor

Is the refrigerant level too low?

A lack of refrigerant (often referred to as “gas”) prevents the system from capturing heat outdoors. This may result from:

• A slow leak

• Improper installation (connections not vacuum-sealed)

• Physical damage to the refrigerant line

AirGreen uses specialized tools to respond:

• Electronic leak detection

• Precise system recharging

• Manufacturer-compliant pressure checks

Faulty sensor or control board: time for a professional diagnosis

Sometimes, the issue stems from a malfunctioning or miscalibrated temperature sensor, which stops the system from entering heating mode. In other cases, the main control board may no longer send the signal to the compressor.

We recently repaired a Sharp ZU1 12,000 BTU in Laval, where the reversing valve board had shorted out: the unit worked perfectly... but only in cooling mode.

Our AirGreen approach:

• Complete electronic diagnostics

• Replacement of original sensors or control boards

• System compatibility verification

Non-compliant installation: a structural issue that needs correction

In some cases, the root problem is the initial installation:

• Piping run too long (beyond manufacturer limits)

• Improper elevation between units

• Multiple elbows reducing efficiency

• Refrigerant lines not thermally insulated

We recently fixed an installation in Saint-Eustache of a Gree Extreme 18,000 BTU, installed with 40 feet of poorly insulated refrigerant piping, which caused major heating loss.

The AirGreen solution: fast response, expert diagnostics, long-term results

When your wall-mounted heat pump blows cold air in winter, every hour counts. We respond quickly in Montreal, Laval, Longueuil, the North Shore, and the South Shore to:

• Pinpoint the exact cause of the issue

• Offer an immediate fix: maintenance, repair, or system adjustment

• Assess whether replacement is a better long-term option, and recommend a model adapted to the local climate

• Provide a clear, surprise-free quote

What to remember to avoid this happening again

• Have your heat pump serviced annually

• Ensure the model is suitable for Quebec winters

• Only trust certified professionals for installation

• Never leave a malfunctioning system unattended for more than 48 hours in winter

Is your heat pump no longer heating? Blowing cold air?

Contact AirGreen today. Our team can quickly step in to diagnose, repair, or recommend a long-lasting solution tailored to your home and winter comfort.