I just had a guy out yesterday who replaced the Rollout Limit Switch on our Coleman/Evcon home furnace. This morning, the furnace kicks on but only runs for about five minutes before you can hear the click of the switch tripping and then the gas flame shuts down. I can manually reset the switch by pushing on the top of it, but that only repeats the procedure. Thoughts?
You definitely have either a cracked heat exchanger or a carbon plugged one. Nasty a job to change exchanger, but it can be done. Coleman says these furnaces average life is 12 years. You can get lots more with proper maintenance. But it might behoove you to just replace the furnace, Propane furnaces are more prone
to carboning up the Secondary exchanger. Look at the out side vent tube... If it is blackened inside..That is a good indicator. Nasty smell in house indicates cracks in exchanger system. Rolloff switch tripping indicates plugged or restricted system. Flame is not being pulled into tube and is rolling off creating a dangerous condition. I recommend calling a professional HVAC Master Licensee ASAP!
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IF YOU LOST POWER WHEN FURNACE WAS RUNNING IT TRIPPED ROLLOUT SWITCHES AND POSSIBLY THE HIGH LIMIT . IN CENTER OF ROLLOUT SWITCHES IS A LITTLE RED BUTTON THAT YOU RESET . YOU CAN ALSO TRY FINDING HIGH LIMIT WITH POWER SHUT OFF TO FURNACE PULL BOTH WIRES OFF HIGH LIMIT AND USE PAPER CLIP TO JUMP BETWEEN THE TWO WIRES MAKE SURE YOU DONT SHORT OUT AGAINST ANY METAL WHEN YOU TURN BACK ON IF IT WORKS YOU NEED A NEW HIGH LIMIT SWITCH.
Limit switches are safeties and require a manual reset. They are also a Normally Closed contact. A hi temp. thermostat operates on its own. If you are sure it is a limit, find the red little button and listen for it to click. Sometimes they push pretty hard.
i hope the heater doesnt come on when a limit switch is open,you really have problems. so a limit is telling you that your furnace it over heating. first check filter and heat vents and returns they must be clean and open. closing heat vent or blocked returns will cause over heating. after chacking this look at firing rate. furnace could be overfired. you would need a "u" gauge to check manifold pressure. your name plate will tell you what this should be. find the tap on the burner manifold or outlet of gas valve. fire furnace and see what it is. 3.5"wc for nat and 10" wc for propane maybe.
How do you test a
pressure switch and other limit controls? This is for people
who are experienced with electrical equipment and the use of a Volt Ohm meter.
*Please never by pass a pressure switch or limit control. The pressure switch
and limit switches are there for your safety. You would
test by setting your volt meter to "Volts AC" and test the rollout switch by
placing one meter probe on one terminal of the rollout switch and your other
meter probe to a good ground. Have the red probe touching the top
terminal of the rollout switch and the black probe touching a ground (body) of
the furnace. You should be getting 25.85 volts which means the rollout is
good on the top terminal. I would next test the bottom terminal of the rollout
by touching the red meter probe to the bottom terminal on the rollout switch and
the black terminal to ground. If I get 25.85 volts on the bottom terminal the
rollout is good. If I do not get any voltage on the bottom terminal then the
rollout has tripped and can be reset (if equipped) by pressing in on the little
button or replaced. If your rollout
switch is tripped you probably have a stopped up heat exchanger or a leaking
heat exchanger. I would recommend calling in a service technician to find out
why the rollout switch tripped. If you have an open limit control either
the furnace has over heated or the limit has gone bad. Problems that would make
a limit open up would be dirty filters, dirty evaporator coil causing a
restriction in the air flow or a slow blower motor (check the capacitor on the
blower motor to make sure it is good). A weak blower motor capacitor will cause
the blower to run slow and eventually fail. Pressure switches, and limit
switches can be tested with a meter in the same manner. With the furnace
calling for heat you can test each of the terminals on the pressure switch to
ground to make sure the pressure switch is closed. You should be getting between
24 to 28 volts from each terminal to ground if the pressure switch is closed. If
the pressure switch is open you either have a stopped up vent, drain line (if
you have a condensing furnace) or bad pressure switch.