Multi-tap Transformers

Senior Tech Bob: “Did you check the transformer Jim?”

Third Year Tech Jim: “Sure did Bob. It’s all wired up.”

Bob: “Is the line side tap set at 208 volts?”

Jim: “Huh?”

When you are installing a new system, especially if it’s in a commercial building or apartment building, make sure the primary tap on the unit’s transformer is set to match the building’s supply voltage. If taps are not connected at the factory, many times they are set on the 240 volt connection. If you’re working in a 208 volt building you’ll need to switch the tap to the 208 volt connection. Incorrect voltage connections often lead to control circuit board issues, contactors chattering or not engaging and relay coils not pulling in.

Jim: “Hey Bob, this is the third transformer that’s blown in this unit.”

Bob: “Did you troubleshoot the circuit for shorts?”

Jim: “No man, I thought we had a bad batch of transformers.”

When a technician burns up three or four transformers, he or she begins to think maybe that’s not the problem. In most cases it isn’t. In most cases it’s symptom of the problem, not the problem itself. Make sure to troubleshoot the components in that circuit for a short.



Don JohnsonDon Johnson is the President of Freedom Heating and Cooling in Birmingham, Alabama which offers home owners tools including:
9 Things to Check Before Calling for Service on Your Air Conditioner or Furnace”,  a resource to help home owners save on HVAC problems
The Home Owner’s Guide to Hiring a Heating and Air Conditioning Company“, a quick read on how to guarantee you never suffer by hiring the wrong contractor.
The Ultimate Home Owner’s Guide to Designing an HVAC System , a 59-page eBook covering the 9 steps to building a Complete Home Comfort System.   Contact him at 205-444-4444 or connect on facebook or Google +