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ADP Garage heater model CUHP - 45A-3 LED flashes 4 times says high limit or rollout switch open. Where are these located? Suggestions to fix? The blower motor isn't kicking on. Exhaust fan and flames work just fine.
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One thing all of have to remember is that there is no one fix - for example went to one tonight that had this same problem - when I checked there was no power to the hi limit and if the rollouts trip ypu have to reset them (this tells you there is a problem and get if fixed, the problem here was a bad connection at the molex plug sso code flashes are idot lights to tell you THE AREA of the issue they are not the telltale problem if your hi limit trips it could be a clogged filer with no air flow cut the wire to the hi limit they will still be a 4 flash code and the problem is different
There may be a small bi-metal switch mounted on the combustion chamber that allows power to the fan at a certain temp. Look at wiring diagram to find or follow power wire back to find it. It also may have a timer relay that may be bad. This unit is made by Advanced Distributor Products or ADP for short.
sounds like the primary limit typically behind the gas valve its larger then the others, rectangle in shape with 2 wires going to it. be careful if your bypassing limit this can create a very hazardous condition
The blower motor kicks on when there has been a 24 volt control failure.
This usually means that a limit switch has tripped.
Most likely that would be a high temp limit switch or a rollout switch.
First, make sure the filters are clean. and the evap coil is clean. If eaither are dirty/clogged, it will partially block airflow, causing the furnace to overheat, causing the high temp limit to trip.
A rollout switch typically trips for three reasons.
1 flame rollout into the burner compartment due to poor airflow.
2 overheating af teh metal plate the rollout is mounted to, due to dirty, old, rusted components.
3 a bad limit switch.
If your unit has an LED light, count the flashes and it will hepl popint out the problem.
(locate the wiring diagram/flash code list, and correspond the flash count, with the code.)
There is a Primary High Limit Switch towards the middle of the furnace, it more than likely needs to be replaced, very common to go out only after a few seasons. Also, you could have a flame rollout switch tripped that will signal the same code, these switches are re-settable and are located on the outer, top and sides of the burner assembly, they’re about ½ inch in diameter with a red push button in the center and two wires “ usually purple” coming off of them.
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