VRV Indoor Unit Mode Control Explanation

A common issue with Daikin VRV systems is that indoor units appear to operate only in heat or cool/vent, not switching freely between all modes. This is often mistaken as a BMS control fault, but it’s typically a system design limitation.

Only indoor units connected to their own BS box can operate independently in heat, cool, or vent modes.

When multiple indoor units share a single BS box, one becomes the master unit and determines the mode for all others on that box. For example, if the master is set to heat, the others can only run in heat/vent mode.

While the BMS can sometimes manage this by using high select or mode-forcing logic, the underlying issue is usually related to poor system design, where units with different heat loads are grouped on the same BS box.

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Lead–Lag Not Rotating — Quick Check (STULZ E²)

Goal: find why the Lead isn’t handing over to Standby/Assist and restore normal rotation/failover.

60-Second Screen Checks (on any unit)

Service → Group → Group Status

I am looking for a supplier for Siemens Actuator.

Siemens

GSD166.1A

AC/DC 24V

Hi everyone,

Does anyone have a Daikin fault code list they could share?

I’m currently dealing with a U4 fault and would really appreciate any advice or information on how to fix it.

I have attached an image for reference

Emergency Cooling Tower Shutdown – SOP

Purpose: Safe, compliant shutdown of cooling towers during emergencies (Legionella, equipment failure, or hazards).

1. Triggers

• Legionella detected above limits

Added Electrical Formula Wheel - This may help someone

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HVAC DESIGN CHEAT SHEET

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1) HEAT LOAD & AIRFLOW (rules of thumb – verify to code)

• Interior airflow: 3.5 L/s per person

• Perimeter airflow: 7.5–10 L/s per person