Hello
Are we supposed to use the service shut off switch while the heat is running to make sure it shuts off? I thought we were only supposed to use “normal” operating controls???
Thanks
Mariann
Nope, don’t do that. Use the thermostat.
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Thanks Brian, that’s what I thought and while taking one of the HVAC courses they said to use it. I did not think that was right. Thanks again
You can use it for your safety, such as removing a panel cover if you choose to do so. But not to test the disconnect.
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Welcome to our forum, Mariann!..Enjoy participating. 
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Thanks Larry! Appreciate the warm welcome
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I’m no HVAC tech but I don’t think it’s great for the equipment to just kill the power when it’s running. Keeping the blower running after the flame or elements shutoff is the intended operation. Admittedly, it’s unlikely to hurt anything once or twice but I see no reason to do that.
Are you sure they didn’t mean to turn it off and be sure it kills power when the equipment is NOT running? I don’t do that either but it would make more sense.
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Most furnaces nowadays have a safety switch tied to the access panel. If the unit is running and the panel is removed, it should shut it down. Some units will go into a fault mode when this is done to protect the electronics. The same thing can happen if you use the disconnect. Unless you know how to reset the unit once it is in a fault mode, do as @bcawhern1 stated. Use the thermostat to fire it up and look through the little window to see the flame (if equipped). Use the thermostat to shut it down, letting it go through the cool down cycle, etc…, then remove the inspection cover.
You don’t want to be responsible for a furnace that won’t restart or heat after you get done with it…
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See something say something. If after consulting on the topic you feel the course is in error, write to education@nachi.org
You may be referring to:
Which does not quite say, but does seem to imply, the service shut-off is a “normal operating control”.
There’s some room for interpretation on what’s normal (I include gate valves operating as shutoffs), but a furnace shutoff is not what I’d consider a normal operating control.
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You can test the safety/service switches using this method…
- Remove furnace service and blower panels.
- Turn thermostat up high enough to call for heat.
- Turn off service switch.
- Install blower panel (or manually hold in safety switch).
- Turn on service switch.
If the furnace starts before step 5, something is amiss. But the biggest benefit of this procedure is not having to book it from the thermostat to the furnace to watch the furnace startup, lol.
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I did it just like Ryan, because I wanted to see the burners start up, etc.
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Like this.
The most common reason you might open the lower panel would be for filter access (some installers forget to put it in the plenum) in which case you would want the blower interlock to operate (turn off the blower - prevent sudden operation without the cover).
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Creative bypass. 
One of the few auto comments I have in my report software. See it all the time.
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Ok, ok. Raise your hand if you sometimes cheat, and hold the blower panel safety switch, so you can get a better view of the burners, briefly at startup…
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Same here. Though with many modern thermostats it doesn’t work like that, because the thermostat is shut off when the switch is shut off.
I haven’t had a problem yet if leaving the service switch on when turning up the thermostat. With the blower panel door previously removed it should not light. This part tests the blower panel switch. Then turn off service switch. Next hold the panel switch in or put panel door on. This part tests the service switch. Finally, turn on the service switch and furnace should light.
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Actually I usually put the blower cover back on before the final step of turning the service switch back on. I used to just use my finger but I didn’t like having to kill the furnace when letting go of the switch to put the cover back on. And yes I have tried, sometimes successfully, to slip the cover on while removing your finger at the last second, lol. But my work is done behind the blower cover at that point anyway, unless the fan starts making a bunch of noise or something.
Right, if you leave the switch on. But if it’s turned off and/or the panel door is removed there is no power to the thermostat.
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Reminder, the OP asked if the safety disconnect should be tested. I would say no. However, that does not change the fact we may use it to safely evaluate the furnace, which would in effect illuminate a problem.
On heat pumps and condenser units, I would not test the safety disconnect or breaker.
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