I had a great time doing some interesting repairs at the Repair Cafe event in Campbell River yesterday. One of the most interesting and challenging repairs was that of a Food Saver plastic bag vacuum sealer, for which the heat sealing wasn’t functioning, but the vacuum function was apparently OK. In this case, the problem was not apparently common heat strip failure, but rather a failed vacuum activated switch. Here’s what I did to diagnose and repair it.
First, after some tests and removal of the back cover, resistance tests of the heater strip turned up OK, a cold resistance of about 3 ohms. However, in-situ live tests done with the unit inverted, by pressing carefully on the plastic parts of the interlocks (while carefully avoiding live 120VAC wiring!) showed no voltage being applied to the heater. The heater voltage, about 20V AC, is normally applied via a 24VDC relay. I tried bypassing that relay with a jumper, and, that caused the heater strip to heat. However, upon taking that relay out of circuit and testing it with a DC power supply, the relay turned out to be functioning normally. After more investigation, I finally tried testing the vacuum-activated switch as shown in the pictures; heat is not normally applied unless sufficient vacuum has closed that switch. That switch turned out to be the culprit; it was stuck with the switch open. Even direct application of system vacuum to that unit from the DC motor intake was not sufficient to close the switch. Dis-assembly showed a spring inside had shifted position and been crushed against one side of the switch. I extracted the old damaged spring, made a new one with a spring out of an old pen, re-assembled, and, voila, the vacuum sealer heater is now working fine. Successful test with a bag showed both vacuum and heat sealing functions to be working well.