Jumpers are simple and sometimes valuable troubleshooting tools for HVACR technicians, but, when misused, they can be very dangerous tools. When properly used, jumpers allow a technician to electrically energize a circuit with an open switch or a series of open switches. This allows the technician to verify the switch or switches are electrically open and energize the circuit to test the complete operation of the system. However, jumpers can create a serious safety issue as well as cause damage to a system if they are used improperly.
When selecting a jumper for a circuit, remember that all of the circuit’s current will be passing through the jumper, so make sure you use one with the proper wire size. Using too small of a wire can cause it to overheat and burn. Always look at the wiring leading to the switch and use a jumper that is equal to or greater in size.
Many jumpers used today have alligator clips to attach the jumper across a switch. Although this is a convenient method of attaching the jumper, it can lead to problems for a technician and the system. Avoid using alligators if the terminal does not allow for a solid connection. A poor connection can cause the alligator clip to jump off and create a short to ground or another part of the circuit.
As a case in point, several years ago, I was jumping out a low-pressure switch used on a walk-in cooler. Shortly after I energized the system, one end of the alligator clip jumped off and touched the cap tube of the pressure switch. This not only blew the circuit breaker, but it also burned a hole in the cap tube and the refrigerant leaked out. A relatively simple repair turned into a more extensive repair.
Alligator clips can also be very difficult to attach to some small terminals, terminal blocks, and control boards. Light-gauge jumpers with magnetic ends are available for use with control circuits and are ideal when working with these small terminals. However, these ends may not work on all terminals. If the terminal screw is made of a nonferrous material, the magnet will not attach to the screw.
It’s a good idea to carry an assortment of jumpers with several different ends. Having an assortment available with various size alligator clips, magnetic ends, female spades, male spades, or any custom end you may need will make jumping a switch easy and convenient.
Jumpers should only be used as a temporary bypass during the troubleshooting process. They should not be left on a system as an “engineered” repair or a permanent fix. This is unwise and, potentially, very dangerous. Also, use extreme caution when placing a jumper across a critical safety. Depending on the type of safety, it may be unwise to place even a temporary jumper across it. You need to use common sense when it comes to which safeties you can temporarily bypass and which you can’t. Some should never be bypassed.
Another important precaution is to never leave a system unmonitored with jumpers in place. This could create a serious safety condition or cause damage to the system.
Early on in my career, I was working on a relatively old air conditioning system with a remote condenser that kept shutting down on its high-pressure switch, so I jumped it out to keep the system running. This was mistake No. 1. Next, I left the system unattended to make a phone call, which was mistake No. 2. While I was on the phone, I heard a loud explosion. Not knowing what had happened, I and several other workers ran out of the building. When we finally went back in we discovered the issue: A section of the discharge line of the air conditioning system I was working on had blown out. The high-side pressure had built up so high that the discharge line gave out. Neither the system nor the compressor had a relief valve in place, which was probably mistake No. 3 (but at least that was not my doing). After investigating the system further, I did find the initial problem: The remote condenser had a defective fan motor that I had not looked at before placing a jumper across the high-pressure switch. So, not only did I have to replace the condenser fan motor, but I also had to replace a section of the discharge line and recharge the system. A lesson well learned.
So, I guess the old saying, “When in doubt, jump it out,” is not really a wise practice to follow.
Publication date: 8/3/2015