| MACURCO - Gas Detection Systems | Louis Horsefield & Associates |
| MAGIC- AIRE - Fan Coil Units | Haldeman, Inc. |
| MAGIC- AIRE - Fan Coil Units | Conditioning Components Co. |
| MAGIC-AIRE - Fan Coil Units | Southern Ca A/C Distributors |
| Make-Up Air Units, Gas & Electric (Gaylord, Modine) Industrial Air Sys. | Air Conditioning Specialties Co. |
| MAMMOTH Heat Pumps | Dockendorf, W.G., Inc. |
| MARKEL - Electric Heaters | Southern Ca A/C Distributors |
| MARLEY - Cooling Towers | DMG Corporation |
| MARS AIR DOORS - Air Curtains | Southern Ca A/C Distributors |
| McQUAY INTERNATIONAL - Entire HVAC Line | DMG Corporation |
| Metal & Aire, Grills/Registers Terminal Equipment | Perfect Air Control, Inc. |
| Metal Bestos Stacks - Boiler - Engines - Grease Duct | Heat Technology Products |
| MG Piping - Expansion Joints | Sausse M.W., & Co., Inc. |
| Minnesota Flexible - Stainless Steel Connectors | Dawson Co. |
| MITSUBISHI - Ductless Air Conditioning | Southern Ca A/C Distributors |
| Modular Chillers (Applied Products) | Air Treatment Corp. |
| Moisture Eliminators (Airsan) | Air Conditioning Specialties Co. |
| Monoxivent - Source Capture | Haldeman, Inc. |
| Mueller Ice Harvester | JD Sales Co., Inc. |
| Mueller Plate HX | JD Sales Co., Inc. |
| Multistack Modular Chiller | JD Sales Co., Inc. |
| Myers - Sumps, Effluent, Sewage Pumps, and Packages | Dawson Co. |