limt tripping

[strick87]

I have a E2EB-015HA FURNACE I AM WORKING ON. WHEN I FIRST LOOKED AT FURNACE THE DOUBLE STACK LIMIT WAS TRIPPING WITH BLOWER DOOR ON. WOULD TAKE OFF BLOWER DOOR AND LIMIT WOULD NOT TRIP. REPLACED LIMIT WHICH IS 190 DEGREE. SAME PROBLEM WITH NEW LIMIT. AFTER TALKING WITH HOMEOWNER HE TOLD ME DID NOT BELIEVE THE AIRFLOW WAS AS GOOD AS IN YEARS PREVIOUS YEARS. I DID NOTICE THE MOTOR WAS DRAGGING A LIITLE BIT. REPLACED CAPACITOR AND MOTOR RAN MUCH BETTER. BETTER AIRFLOW THROUGH REGISTERS. HOMEOWNER WANTED TO REPLACE MOTOR. REPLACED MOTOR AND CAPACITOR. THIRD HORSE 1075 RPM. AIR FLOWER EVEN BETTER WITH HIGHER RPM MOTOR. RAN FINE FOR ONE WEEK THEN GOT A CALL LIMIT DROPPING OUT AGAIN. HE DETRMINES THIS BY TEMP OUT OF REGISTERS. WITH ONE ELEMENT 90 DEGREE SUPPLY AIR TEMP AT 68 RETURN TEMP. WITH ALLTHEE ELEMENS 123 DEGREE SAT. WHEN DOUBLE STACK LIMIT DROPS OUT HE GETS THAT 90 DEGRE SAT. SO THAT GIVES US ABOUT 55 DEGREE RISE. EVAP. COIL LOOKS CLEAN FILTERS CLEAN NO REGISTERS SHUT OFF. WHEN I PULL LIMIT OUT AND CHECK SAT IN THE HOLE I REMOVED LIMIT FROM READ 192 DEGREES. NOT SURE WHY SUCH HIGH SAT AT LIMIT LOCATION. BUT I BELIEVE THAT IS WHY LIMIT IS TRIPPING.

[Robert]

Hi,

You cannot look at an a-coil and determine if it is clean or not. Need to test airflow across filter and across a-coil.

Ensure you are getting proper cfm through the furnace and across the element coils.

Also, those sequencers work on a timing pattern and you will not always have all elements on at once.

Ensure that the limit is in fact tripping.


Thanks,
Robert