MT+Plus

Not because of anything in the file. Browsers and Windows are wary of any program few people have downloaded yet, more so when it isn't code-signed, and MT+ is both new and unsigned.

Code signing is a digital signature on a program, made with a certificate the publisher buys each year from a company that checks who they are. It lets Windows show the publisher's name and trust a new program sooner. It's a yearly cost aimed at software companies, and it isn't practical for a free tool right now.

Keep the download and run it:

• Chrome: open your downloads (Ctrl+J), find MT+ and choose Keep. Some versions word it Download suspicious file.
• Edge: in the downloads panel, hover over MT+, open the … menu and choose Keep, then Show more and Keep anyway.
• Windows: if a blue Windows protected your PC box appears when you run the installer, click More info, then Run anyway.

To be sure it's the file we posted, compare its checksum with the one under Verify the installer, and only download MT+ from vrftools.com. If a company laptop won't run it at all, that's an IT policy on unsigned programs; your IT department can allow it.

Most of MT+ only reads from the equipment. Some tools write settings or command units, and a tool like that, misused on a live system, can cause real trouble. The tiers match each tool to how much it can do and how much field testing it has had. The basics work for everyone with no code, and each tier includes everything below it.

DSGs get new tools first. The DSG tier has early access to new functions, so they're thoroughly tested in the field before they're released to lower tiers. Once a tool has proven itself, it moves down the ladder for everyone. Evac Mode, for example, started out DSG-only and has since moved down to Certified.

Only for the Certified tools; everything in Basic works without it. Certified unlocks tools that command the equipment instead of just reading it, such as Port Verification. Those tools are meant for techs who have been through Mitsubishi Electric's training class, so the quiz asks questions you'll know if you have.

The quiz isn't open yet. Until it is, a DSG can vouch for you with an Advanced code, which includes everything Certified has.

The tools that read (the address search, DIP switches, error history, function settings) only ask units for information; they don't change how anything runs. Tools that write settings or command units can, just as Maintenance Tool can. That's why MT+ groups its buttons into Read, Write and Command rows, why the stronger tools sit behind tiers, and why command tools carry their own safety checks whatever your tier: Evac Mode won't run until every indoor unit is detected off.

Like any service tool, it's only as safe as how it's used. Know what a tool does before you run it on a live system; every tool has a help page in MT+. See the Disclaimer & Terms of Use.

Yes. There's no price, no subscription and no trial that runs out. Activation codes are free too: the tiers are about trust, not payment.

MT+ does ask you to join the VRFTools newsletter when it starts. You can close the prompt after a few seconds, and once you subscribe and confirm the email, it stops asking. VRFTools runs on donations, so if MT+ saves you a trip, a beer helps keep it that way.

No. The basics work offline with no account. You need a connection once, to redeem a code; after that your key is stored on the laptop and works offline. When there is a connection, MT+ also checks for updates and sends any feedback you choose to send.

Only your email and code when you redeem, and your email when you subscribe to the newsletter or MT+ checks whether you have. Feedback carries what you typed, which tool, your tier and the MT+ version, with no email and nothing that names your PC.