| Employer | State | City | |
| C J Erickson Plumbing Co | Illinois | Chicago | View Profile |
| Cam-Ful Industries | North Carolina | Pineville | View Profile |
| Cam-Ful Industries | North Carolina | Pineville | View Profile |
| Carter Goble Lee Company | Georgia | Alpharetta | View Profile |
| Cary Services Inc | Texas | Abilene | View Profile |
| Cavanaugh Electrical Contracting | Pennsylvania | Wilkes-Barre | View Profile |
| CCI Mechanical, Inc. | Utah | Salt Lake City | View Profile |
| Central Carolina Air Conditioning | North Carolina | Greensboro | View Profile |
| Central Florida Store Services Inc | Florida | Sanford | View Profile |
| Christian Brothers A/C | Texas | Austin | View Profile |
| Christian Brothers A/C | Texas | Austin | View Profile |
| Christian Brothers Heating & Air Conditioning, Inc | California | Mira Loma | View Profile |
| CITY OF LOS ANGELES | California | Los Angeles | View Profile |
| Classic Air | Georgia | Norcross | View Profile |
| Climate Control Company of Glenwood Springs | Colorado | Glenwood Springs | View Profile |
| Climate Heating & Cooling | Massachusetts | Dalton | View Profile |
| Climate Technology | Colorado | Colorado Springs | View Profile |
| ClimateCraft | Oklahoma | Oklahoma City | View Profile |
| CLIMATIC REFRIGERATION & AC | Florida | Melbourne | View Profile |
| Clover Contracting, Inc. | Virginia | Fairfax | View Profile |
| CLP | Texas | Austin | View Profile |
| CMS Mechanical Services, Inc. | Colorado | Windsor | View Profile |
| ColonialWebb Contractors | Virginia | Richmond | View Profile |
| Colony Air Conditioning & Heating | Texas | Lewisville | View Profile |
| Colt Plumbing Co | Pennsylvania | Mechanicsburg | View Profile |
| Colt Plumbing Co | Pennsylvania | Mechanicsburg | View Profile |
| Comfort Air Systems, Inc. | Massachusetts | Framingham | View Profile |
| Comfort Flow Heating Company | Oregon | Springfield | View Profile |
| Comfort Products Distribu | Nebraska | Omaha | View Profile |
| Comfort Products Distribu | Nebraska | Omaha | View Profile |
| Comfort Systems USA - Ohio | Ohio | Oakwood Villiage | View Profile |
| Commercial Mechanical Systems, Inc. | North Carolina | Raleigh | View Profile |
| Commercial Service Innovation, Inc. | Iowa | Bondurant | View Profile |
| Comprehensive Energy Serv | Florida | Longwood | View Profile |
| Comverge, Inc. | Georgia | Norcorss | View Profile |
| Constructors & Associates | Texas | Dallas | View Profile |
| Control Air Conditioning | California | Anaheim | View Profile |
| Controlled Environment Technologies | Pennsylvania | York | View Profile |
| Cottongim Heating & Cooling, Inc. | Georgia | Tifton | View Profile |
| Cottongim Heating & Cooling, Inc. | Georgia | Tifton | View Profile |
| County Air | California | Orange | View Profile |
| Crockett Facilities Services, Inc. | Maryland | Bowie | View Profile |
| Cropp-Metcalfe | Virginia | Faifax | View Profile |
| Cropp-Metcalfe | Virginia | Faifax | View Profile |
| Crown Heating & Cooling, Inc. | Ohio | Union Town | View Profile |
| Crown Heating & Cooling, Inc. | Ohio | Union Town | View Profile |
| Crowther Roofing & Sheet Metal | Illinois | Lockport | View Profile |
| CTC Supply Inc. | North Carolina | Fayetteville | View Profile |
| Curtis Total Service, Inc. | Pennsylvania | Allentown | View Profile |
| Custom Mechanical Services | Connecticut | Bristol | View Profile |