Fan limit switch issue.
Ok I just replaced an old camstat 57E-25T-110-20 Fan limit switch because it was not staying closed when the furnace was cold from not running. Basically the limit switch was doing the opposite of what it was supposed to. It never hit the high limit when the furnace was running it just had issues staying closed when the weather got real cold and furnace was not running.
Example: at night I drop the thermostat 6 degrees but in the morning when the thermostat calls for heat the switch won’t make contact and fails to close, thus no heat. It would eventually start working again but struggled. I measured the voltage as it was trying to make contact and it goes anywhere from .500v-26v eventually settling out at 26 volts and kicking the gas value in gear. Once it on it’s good to go and will run until the thermostat is satisfied but if it sits to long then it does it all over again. I have gotten around this by not dropping the heat at night.
After all this I decided the switch was bad and ordered a 57C-05T-120A which is considered the replacement for this switch. The only real difference is the old switch is not adjustable and has a static limit set at 200 degrees F. The new switch is adjustable and was pre-set at 200.
Here's my new issue: The new switch has no problem kicking on when it’s cold but now it’s hitting the high limit and shutting off the burners after about 10- minutes. So basically I traded one problem for another. I find it strange that the old switch never hit the high limit and actually only worked when the burners remained on but the new sitch is hitting the high limit within 10 minutes. Any thoughts on the issue?