Klein MM420 Review: My Go-To HVAC Multimeter
After five years in HVAC, I’ve burned through my share of cheap multimeters. The Klein MM420 changed that. This thing handles everything I throw at it—from checking 24V control circuits to testing compressor windings in hundred-degree attics. The auto-ranging feature saves time when I’m bouncing between voltage checks and resistance readings, and the TRMS actually matters when you’re diagnosing variable-speed equipment. What really sold me was durability. I’ve dropped it off a condenser unit, left it in the rain, and it keeps working. The leads are thick enough to survive daily abuse, and the display stays readable even in direct sunlight. At this price point, you won’t find a tougher, more reliable meter for HVAC work. It’s been in my bag every single day for two years.