Mitsubishi Electric Air Conditioner Not Heating? 7 FAQs From a Melbourne HVAC Coordinator

I'm a mechanical services coordinator in Melbourne. For the past eight years, I've specified Mitsubishi Electric air conditioning for commercial fit-outs, apartment upgrades, and the occasional high-end renovation. I've personally made and documented five significant mistakes along the way — totalling roughly $12,000 in wasted budget. The worst part isn't the money; it's the look on a client's face when they lose trust in your judgement.

Now I maintain our team's pre-ordering checklist, and since we formalised it in 2023, it has caught 47 potential problems before they ever reached a site. Builders, body corporate managers and homeowners ask me the same questions every winter, usually starting with the phrase: my Mitsubishi Electric air conditioner is not heating. This FAQ is based on those real conversations. Everything here reflects what I've seen in Melbourne as of January 2025 — not a replacement for your manual or a licensed technician.

Mitsubishi Electric air conditioner not heating? What should I check first?

Start with the boring stuff. In my first year (2017), I attended two emergency callouts that were just settings and a timer. So before calling anyone:

• Check the remote is in heating mode, not cool, fan or dry, and set the temperature a couple of degrees above the current room temp.
• Wash the air filters. Dirty filters are basically the most common physical cause I see on split systems: the unit runs, but airflow drops and warm air never reaches you properly.
• Check the outdoor unit for leaves, rubbish or plants blocking it. The outdoor coil needs to pull heat from the outside air — even in a Melbourne winter — and it can't do that if it's suffocating.
• Check timers and clocks after power outages. I've seen sleep timers from months earlier switch units off at 11 pm and nobody remember setting them.

If you've done all that and it still isn't heating after 20–30 minutes, turn it off at the circuit breaker, wait five minutes, then restart. Still cold? You're now looking at a refrigerant leak, a stuck reversing valve, or a failed sensor. That's when you get a licensed Mitsubishi Electric accredited service provider involved. And no, not a handyman who knows air cons. I learned that the expensive way.

Why is my Mitsubishi Electric air conditioner blowing cold air in heating mode?

First question: for how long? There's a big difference between a normal defrost pause and a genuine fault.

A reverse-cycle heat pump extracts heat from the outside air. In winter, frost builds on the outdoor coil, and the unit periodically reverses itself to melt that frost. During defrost, which usually lasts five to ten minutes, you may hear the note of the unit change, see steam around the outdoor unit, and feel cooler air indoors. That is normal operation, not a breakdown.

What's not normal is 20 minutes or more of steady cold or lukewarm air. In my experience, the usual causes are a reversing valve stuck in the wrong position, low refrigerant, or a faulty temperature sensor. I had a client in September 2022 who ignored that symptom for two weeks because they assumed it was just the defrost cycle. It was a failing four-way valve, and the wait turned a straightforward repair into a longer shutdown. If the cold air is continuous, stop diagnosing and call the service team with that specific detail.

Frost on the outdoor unit — is my system faulty?

Some frost is completely normal when the outdoor temperature sits around 5°C and the air is humid. A healthy unit frosts up, clears itself with a defrost cycle, then repeats. The steam produced during defrost looks dramatic — particularly against a dark winter sky — but it's just melted frost evaporating.

What should make you suspicious:

• a solid block of ice that never clears,
• frost only on part of the coil, or
• defrost cycles firing every few minutes with little heating in between.

Those signs usually mean poor airflow around the outdoor unit, low refrigerant, or a faulty defrost sensor. I caused a textbook case in 2021 by approving an outdoor unit position with barely enough clearance on one side. It iced up on cold nights, and relocating it cost $900. The Mitsubishi Electric unit never had a fault; the siting decision did.

Should I repair or replace my Mitsubishi Electric heat pump?

My rule of thumb: if the system is more than 10 years old, if the refrigerant type is getting expensive to source, and if the repair estimate is more than roughly a third of a replacement cost — replace it. If it's a simple fix like a capacitor or fan motor on a six-year-old system, repair it.

But the calculation shouldn't be purely dollars. Room temperature is part of how people judge a building. I once had a client who kept patching an ageing heat pump through multiple winters rather than replacing it. They spent $1,400 on stop-gap repairs, and their tenants spent a full season cold. When the system finally failed, it wasn't just a maintenance issue — it was a reputational one.

Your building feels cold is never just a technical complaint. It's a comment on the whole management.

I'm not saying every project needs the top-tier option. I am saying that quality — of equipment and installation — shows up in how your space feels, and that feeling is the brand experience your occupants take away.

How do I choose a Mitsubishi Electric dealer in Melbourne?

This is the most common question I get from property managers, and it's the right question to ask. The same Mitsubishi Electric model can perform brilliantly or poorly depending on who installs it.

Here's what we check when we look for a Mitsubishi Electric dealer in Melbourne:

• Accreditation. Ask directly whether they're a Mitsubishi Electric accredited dealer. Not every air conditioning contractor is, and accreditation is relevant for warranty and service support.
• A site visit. If a dealer quotes over the phone without checking ceiling height, insulation, window area and orientation, walk away. I approved a no-site-visit quote in 2018 and ended up with an undersized unit that could not heat the space properly. That mistake cost me a client.
• Proper load calculation. Good dealers calculate the heating load rather than guessing one kilowatt per square metre. The difference is huge in older Victorian buildings.
• Local service response. Ask what happens if the unit fails in July. A dealer who can't promise a quick response isn't the right dealer for a commercial space.

The cheapest quote often becomes the most expensive project — I've seen it from both sides. Paying a fair price for an accredited installer isn't luxury; it's protecting the reputation of the brand you're putting your name behind.

Why would a brand-new Mitsubishi Electric system stop heating in its first winter?

This is the question nobody thinks to ask until it happens. And in almost every case I've investigated, the equipment wasn't the problem — the installation was.

One of my biggest regrets is from September 2022. I approved a multi-split replacement on a tight deadline and agreed to a friend-of-a-friend installer to save around $1,800 in labour. The system started up fine, but the heating was weak from day one. An accredited technician found the refrigerant lines hadn't been properly evacuated and the unit was overcharged. Fixing it cost another $1,200, and the client's confidence in Mitsubishi Electric took a hit because of my shortcut.

The name on the outdoor unit is only half the product. A quality brand deserves a quality specification and a quality installation. That's why I now write install by an approved or accredited Mitsubishi Electric dealer into contracts, rather than just a model number. It's a small line that would have saved me thousands.

Can a ceiling fan help with heating — and how do I install one safely?

A ceiling fan can genuinely help in the right space. In rooms with high ceilings, warm air collects near the ceiling while everyone downstairs complains about being cold. Running a fan on low speed in winter mode pushes that warm air back down without creating a draft. I've specified that setup in apartment lobbies and open-plan offices around Melbourne.

If you're searching for how to install a ceiling fan because you want to improve heating airflow, the key points are position and fixing. The fan needs to be securely anchored to the ceiling structure — not just to plasterboard — and installed at a safe height. If it includes a light kit with glass shades, such as frosted or milk glass for softer light, those add weight and wiring complexity.

The honest answer is that most people shouldn't install one themselves. Ceiling fans connect to fixed electrical wiring, and in Victoria that means a licensed electrician unless you hold the right licence. I've seen DIY fans wobble, hum, and in one case come loose from a ceiling bracket. Have an electrician do the physical installation, then set the direction switch to low for winter and let it circulate the warm air your Mitsubishi Electric system is producing.