Error code reference

Lennox Heat Pump Error Code DS2:FAST Flash / DS1:ON

Discharge line temperature lockout

Lennox codes Lennox heat pump codes

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Diagnostic procedure

The full DS2:FAST Flash / DS1:ON procedure

Step 1 is visible so you can confirm you are on the right page. The remaining steps, the ones that tell you whether to actually replace a part, unlock with any pass.

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First diagnostic step

Check discharge sensor for short; check system charge and operating pressures. Reset by cycling OFF 24V power or shorting TEST pins 1-2 seconds.

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More steps, wiring diagram references, and verified part numbers

Includes expected resistance and voltage values, connector pinouts, and supersession notes for replacement parts.

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The full DS2:FAST Flash / DS1:ON procedure

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