I NEED A FAN LIMIT SWITCH FOR A LUXAIRE GSU137MF. dO YOU HAVE A PART NUMBER OR KNOW WHERE i CAN ORDER ONE?

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It's always possible that the limit "dial" switch is sticking leading you to believe that it's only at 150º.

How old is the furnace and when was it last cleaned.

If this is a "Timed run-on" fan then the fault is almost certainly on the small Printed Circuit Board that controls the Fan.

There are two Electrolytic Capacitors on the Board: A 47uF@16V near the timer Control Pot which fails giving a symptom of pulsing or hunting. The second is a 350uF@16V which is near the 14 Pin DIL Chip and controls the run-on timer duration. Both components are easily replaced and this will restore the fan to full function.

You might check the light limiter, a.k.a. wattage limiter. Check the manuel for the location. F you dont have one you can find one on the hunterfan.com sight. Some of the fans only support low wattage lights bulbs (candelabra light bulbs) 60 watts and lower. You might have to open the light limiter to check for burn marks. If there is you need to buy a new one. And if you cant find the lights at a store you can always find them at a online store.

LUXAIRE MAKES NICE REASONABLY PRICED FURNACES IF MAINTAINED PROPERLY WILL LAST A LONG TIME EFFICIENCY RATINGS UP TO 98% IN THE FULLY MODULATING MODEL. ALSO LOWEST PRICED CONDENSING SINGLE STAGE ,PSC FAN MOTOR 95.5 % EFFICIENT. THEN THE ONE THAT I INSTALL THE MOST BEST VALUE FOR YOUR DOLLAR THE 2 STAGE VARIABLE SPEED MODEL 96% EFFICIENT .THE FAN IN THIS UNIT SAVES AN AVERAGE OF $ 135 A YEAR COMPARED TO A REGULAR PSC TYPE FAN MOTOR. BEEN INSTALLING LUXAIRE FOR OVER 25 YEARS AND HAVE HAD GREAT RELIABILITY FROM THEM.

this means a limit switch is open, or the thermostat is set to fan on, as opposed to "auto".
Unplug the unit, then plug it back in and watch the sequence.

If it goes through it's normal operation and then the burners shut off, it means the high limit has been triggered. usually this means the furnace is suffocating, remove your filters and try again.
If it works fine the second time you just need new filters. if not then the high limit is bad.
The high limit is inside, near the burners on the back wall connected to 2 wires.
it's easy to replace, order a new one (be sure to get the right temperature setting, it's on the old one). pull the old one out and plug the new one in. the wires don't have sides as long is one is in Common or C, and one is in NC.

If the main fan comes on first and the furnace does not cycle, it means a limit is open (or the thermostat is in fan on mode). The rest of the limits are on the same circuit as the high limit, trace that circuit and push the button on each switch along the way, if one clicks you know you've reset it... you also know that it has been set off, which implies a safety hazard and technically you should call a pro to come see it.
Anyway, continue along the circuit checking each one until you've come to the main circuit board. then plug the furnace back in and watch it go. if that hasn't fixed it, call a professional.

Try the heat limit switch it could be stuck open take it out and clean the back off it

Sounds like it could be your transformer. See if you can locate it. It should be in the air handler indoors. Check the voltage going to the transformer and check the output of the transformer. You should have around 24 vac on the output of the transformer. If you don't have voltage on the output make sure you have it on the input (120vac). If you don't have it on the input you need to find out why. If you have it on the input but don't have an output then your transformer is likely gone bad. Let me know what you find.

ther might be dip swiches on the circuit board you might have to change

If the snap switch is not located close enough to the plenum, this can be problem. The other option would be to cover the switch area with a metal shield or liatherm paper (fire rtardant paper).