A contractor contacted Johnstone Technical Support about performance issues with a furnace after an inducer replacement. The initial measurements revealed concerning performance characteristics: low fan speed was measuring -1.0"wc pressure, drawing 0.25 running amps, with 121 volts on the low-speed wire. The low-pressure switch, rated at -0.92", was experiencing pressure drops below the recommended threshold.

Typically, we are looking for -0.4 to -0.5"wc MORE vacuum than the negative pressure switch rating to consistently prove and maintain the closure of the switch contacts.

Model Number 

GMEC960603BNBA

Technical Diagnostics

Detailed measurements showed additional complexity:

• High-speed mode measured 121 volts on the Black motor speed wire
• Recorded -2.0"wc pressure during high-speed operation
• Amperage measured ranged from 0.39 to 4.0 amps (against a motor rating of 0.5a)

Problem Resolution

The solution involved replacing the inducer, which successfully resolved the issue. After replacement, the low stage was pulling -1.3 to -1.4" of pressure, indicating improved performance. Johnstone technical support acknowledged the resolution while expressing mild concern about the initial fan's performance not meeting requirements.