by Howard Leonard
Many service technicians have difficulty recognizing when a contactor can be justifiably condemned. Almost any contactor that has been in the system for even a short while will have burnt-looking contacts. So how do you tell when the contacts are too burnt?
There are two things you want to look for while inspecting the contacts.
First, look for splattering of little solidified globules of silver stuck to the contact and its mount. These globules of solidified silver are what’s left over from the coating put on the contact points for increased durability. It has sprayed off of the contact because of excessive heat caused by high resistance connections between the mating points. These small drops of silver mean the coating is gone and the contactor’s days are numbered.
Second, check the edge of the contact point (see illustration). This edge should be intact. If it’s caved in, this indicates that the contact point has been too hot.
When you do find a contactor that’s failing, ask yourself why. Often it’s simply because of old age but not always. Here are some reasons contactors fail:
- The contactor is too small for the load. The inductive (not the resistive) ampacity should be used to size the contactor.
- The compressor is hard starting due to defective run and (or) start components, refrigerant flood back, locked rotor compressor, compressor short cycling, or low line voltage.
- Debris between the contactor points. Never file points. Filing points removes the protective silver coating.
- Low control voltage at the contactor coil. If it’s dropping below 20 VAC during start-up, the contactor may be dropping out. This is certain death for the contactor.
Here’s the bottom line: There are many contactors out there that legitimately need to be replaced. You can do your customer a service by preventing an impending failure and make more money at the same time. Is this a great world or what?
Howard Leonard is president of Total Tech HVACR Training, Phoenix, AZ. He can be reached at 602/943-2517.