Dixell/Copeland F16

What does Dixell/Copeland F16 mean?

On the Dixell IC100CX iChill controller, DF16 controls whether the low-pressure alarm monitoring is active or suppressed during a defrost cycle. Set DF16 to 0 to disable low-pressure alarm detection during defrost (recommended for heat pump systems where suction pressure drops during defrost). Set DF16 to 1 to keep low-pressure alarm active throughout the defrost cycle.

Symptoms

• Low-pressure alarm trips during defrost cycles (DF16 = 1 and suction pressure drops below LP setpoint during defrost).
• Unit locks out from low-pressure alarm during every defrost when it should continue running (DF16 = 1 causing nuisance trips).
• Low-pressure protection is fully inactive during defrost even if a genuine low-pressure fault occurs (DF16 = 0).

Common causes

• DF16 = 1 on a system where suction pressure legitimately drops during defrost mode, causing nuisance low-pressure trips.
• DF16 = 0 bypassing low-pressure protection entirely during defrost — acceptable on some systems, risky on others.
• Compressor running in defrost mode (reverse cycle) with normal low-pressure thresholds not suited for defrost conditions.

Diagnostic steps

1. 01

   Assess whether LP alarm trips during defrost

   Confirm if the low-pressure alarm is triggering during defrost cycles specifically. Check the alarm log on the IC100CX to correlate alarm times with defrost periods.

2. 02

   Set DF16 per system design

   Access the DF sub-menu and set DF16 = 0 to suppress LP alarms during defrost on heat pump systems where suction pressure drop during reverse cycle is normal. Set DF16 = 1 only if LP protection is required during defrost.

3. 03

   Review DF17 low alarm delay after valve switching

   DF17 sets a delay for the low-pressure alarm after the 4-way valve changes state (for systems with DF08 and DF09 = 0). Confirm DF17 is set to allow pressure stabilization after valve switching without tripping the alarm.

4. 04

   Verify refrigerant charge

   Even with DF16 = 0, if LP alarms appear during normal heat pump operation outside of defrost, check refrigerant charge — a genuine refrigerant shortage requires correction.

5. 05

   Check suction pressure during defrost

   Monitor suction pressure with manifold gauges during a defrost cycle. Expected behavior during reverse-cycle defrost is a suction pressure rise. Abnormally low suction during defrost may indicate a restriction or valve issue.

When to call a professional

If suction pressure is genuinely low during defrost cycles rather than the normal reverse-cycle pressure response, a licensed refrigeration technician should assess the refrigerant circuit and 4-way reversing valve operation. Refrigerant-side diagnosis and valve assessment require proper EPA certification and specialized diagnostic tools.