Trane has been using contactors to switch heating elements forever, as did GE before Trane took over, so it is far from a new thing. It is very rare to find those contactors bad too.

Originally posted by grodan1
Fair enough. I'll check it out, but the contactors were not wired to the elements to be fair to me.My memory tells me these "sequencers had low voltage connections for the "load" of the switch, and separate connections for the power they were passing, but I will make sure.Limit switches don't have the same visual as sequencers, so I know I'm right.

Check it real close. There are units out there that have double pole limits that serve 2 heating elements. They have 2 sets of contacts in them with 4 wires going to them, and look almost like single pole heat sequencers. They are really limits though.

Generally a heat sequencer or contactor will not be wired directly to the heating element. They may be wired from the sequencer/contactor to a fuse link, then from the fuse link to the limit, then from the limit to the element. Some will be wired from the sequencer/contactor, to the limit, to the element.

I prefere to have them to be wired from one side of the line to the sequencer/contactor to the limit, then to one end of the heating element, then from the other end of the heating element, to the fuse link and to the other side of the line.
That way there are safeties that can kill both sides of the line voltage to the element if it fails and shorts against something.

Same instructor said you could get total cfm from a gas furnace by amping out blower motor and using formula amps x volts = watts x 3.413 = BTU'S and dividing TD x 1.o8 into those BTU'S!Insane.
Ummm, hate to break it to you, but you can't get the total CFM through a GAS furnace that way....

Determining CFM through a gas furnace doesn't involve amps or volts at all, since you cannot calculate how many BTU's are being put into the air by doing any electrical measurement.
Really, you would need to know the CFM through the furnace to figure out exactly how many BTU's of heat were being put into the air anyway...

Manometers and fan data charts are your friends.

Some manufacturers have a chart where you can determin the CFM based on the TD and ESP of the furnace at certain blower speeds, but the charts, assume some varriables that may not be true with BTU per cubic foot of gas and altatudes that are different from whatever they tested at in the lab.