This month’s troubleshooting situation involves a Rheem RRMA-A048JK10X gas pack. The customer called for service because, instead of warm air being delivered from the supply registers, all they are feeling is cold air.
When you remove the service panel and check the fault code light on the printed circuit board, you note a sequence of three flashes. When you confirm the code as “High limit switch protection device open,” you take the next step of checking the wiring diagram (Figure 1).
After disconnecting the power supply and confirming that the MRLC (Manual Reset Limit Control) located in the burner compartment is not tripped open, you take the next step and locate the LC (Limit Control) located in the blower compartment. When you disconnect the wiring and check this control with an ohmmeter, it shows continuity.
After re-installing the service panels and restoring the power supply, you note that the Draft Inducer Motor and Indoor Blower Motor starts, then, after an appropriate delay, the ignition system functions and the burners ignite.
Allowing the cycle to continue and monitoring the operation of the equipment, you note that after several minutes of run time, the burners turn off and the fault code light again shows three flashes. When you disconnect the power supply, remove the blower motor access panel, and check the LC, your meter shows OL.
A short time later, checking the LC shows continuity.
Based on the results of your testing, you use a dual port manometer to check directly at the return air inlet of the equipment and directly at the supply air outlet. Your manometer shows a TESP (Total External Static Pressure) of 1.2” w.c.
Your troubleshooting question: What is the next step you need to take in servicing this equipment?
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Publication date: 1/07/2019