
Loose Electrical Connections in HVAC Equipment
The picture to the top left is a picture I took after repairing a large rooftop unit where a loose electrical connection almost started a fire in a commercial building. You will see a large fuse and two smaller fuses that have an indication of smoke on them. There is also a fuse block in the middle part of the fuse block melted completely away.

Disconnect Box with Loose Electrical Connections
Loose Electrical Connections in HVAC Equipment: Methods of Testing
Working in a new data center we tested all the electrical and the mechanical equipment. Part of the tests was initial basic checks of the equipment before testing began. Part of the basic check was checking for loose electrical connections inside the equipment. Other things tested was the electrical connections on the batteries in the battery room. A data center can use hundreds of batteries for backup power if the power goes out. Since data centers have redundant power sources the batteries allow for power during the transition time from one power source to back-up. Putting the batteries under load an electrician used a thermal imaging camera to check all the connections on the batteries.
Surprisingly enough there were several loose connections found on the batteries that were tightened up. Whether you have a data center or you are just a homeowner these things need to be checked and preferably by someone qualified for safeties sake.
As always, SAFETY FIRST, make sure power is off before doing these checks!
Loose Electrical Connections in HVAC Equipment
Technical Resource: Refrigeration and Air Conditioning Technology