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Daikin Software Engineer Interview Guide

Daikin Software Engineer interview guide: reported rounds, questions and how candidates describe the process.

The 60-second brief

At Daikin, a Software Engineer plays a vital role in transforming global climate control and industrial manufacturing through intelligent technology. As a world leader in HVAC/R (Heating, Ventilation, Air Conditioning, and Refrigeration) solutions, Daikin relies on software engineering to power everything from embedded unit controllers and smart edge devices to cloud telemetry platforms, automated manufacturing systems, and enterprise tools. In this position, your work directly impacts product efficiency, environmental sustainability, and end-user comfort. Whether you are developing low-level C/C++ firmware for commercial chillers, engineering cloud services to analyze sensor streams in real time, or optimizing complex database systems that support global operations, your code touches critical infrastructure.

This guide is scoped to a Software Engineer candidate at Daikin.

Focus areas

  • Software Engineering Fundamentals
  • Technical Interview Preparation
  • Manufacturing Process Knowledge (Domain)

The Daikin interview process

Daikin candidates report 4 rounds over 3-5 weeks. The stages below are what candidates describe, not a published process.

Phone Screening

Initial call conducted by HR to assess candidate fit and discuss the role.

What to demonstrate

  • Initial call conducted by HR to assess candidate fit and discuss the role
  • Depth in Software Engineering Fundamentals

How to prepare

  • Be able to walk your CV end to end in two minutes, and say why this company specifically.
  • Have your salary expectations, notice period and location constraints ready, and ask for the rest of the loop in writing.

Technical Interviews

Series of interviews focusing on technical knowledge and problem-solving skills.

What to demonstrate

  • Series of interviews focusing on technical knowledge and problem-solving skills
  • Depth in Software Engineering Fundamentals

How to prepare

  • Answer aloud and timed: Write a complex SQL query to extract and aggregate operational telemetry data across relational tables.
  • Answer aloud and timed: Explain the key differences between synchronous and asynchronous execution in cloud services.

Behavioral Interviews

Interviews that evaluate past experiences and cultural fit within the team.

What to demonstrate

  • Interviews that evaluate past experiences and cultural fit within the team
  • Depth in Software Engineering Fundamentals

How to prepare

  • Prepare three examples from your own work, each with a decision you made and an outcome you can quantify.
  • Re-read the description of the behavioral interviews above and write down what you would ask to confirm before it.

Stakeholder Engagement

Engagement with multiple stakeholders, including hiring managers and team members.

What to demonstrate

  • Engagement with multiple stakeholders
  • Including hiring managers and team members

How to prepare

  • Answer aloud and timed: How would you design a software feedback loop to regulate temperature and airflow in a commercial unit?
  • Answer aloud and timed: What factors count toward calculating heat load and deciding unit positioning for optimal climate control?

Where candidates lose points

Prepare for Cognitive & Aptitude Assessments

Be ready for timed numerical, logical, and verbal reasoning tests. Practice basic mental math and logic puzzles under time pressure before taking the assessment.

Emphasize Practical Application

When describing past projects, highlight real-world constraints—such as execution time, memory usage, network reliability, or hardware safety—rather than purely theoretical concepts.

Demonstrate Respect for Manufacturing Operations

Highlight experience where you successfully collaborated with non-software teams, such as production crews, technicians, or quality control managers.

Questions & practice

How do you handle memory management and pointers in C/C++ when developing resource-constrained software?

Medium · Technical & Software Fundamentals

Approach

  1. Say what the runtime actually does before reasoning about the code.
  2. Name what is shared across threads and what owns each piece of state.
  3. Identify the window where an invariant is briefly untrue.
  4. Distinguish a value from a reference to it, and say which one you handed out.

Follow-up

  • What happens if two callers reach this at the same time?
  • Where could this allocate more than you expect?

Explain the key differences between synchronous and asynchronous execution in cloud services.

Medium · Technical & Software Fundamentals

Approach

  1. Say what the runtime actually does before reasoning about the code.
  2. Name what is shared across threads and what owns each piece of state.
  3. Identify the window where an invariant is briefly untrue.
  4. Distinguish a value from a reference to it, and say which one you handed out.

Follow-up

  • What happens if two callers reach this at the same time?
  • Where could this allocate more than you expect?

Identify the heaviest tenants in a five-minute window under memory pressure

Medium · top-k · heavy hitters · streaming

The edge service handles about 3,000 requests per second across roughly 50,000 tenants, peaking near 9,000. Expose the 50 heaviest tenants by request count over the trailing five minutes so limits can be tightened before one tenant's backfill starves the fleet. You may not retain five minutes of raw records. Give the exact solution and its memory, then the bounded-memory approximation with its error stated as a formula, and say which you would ship and at what tenant cardinality that choice changes.

Approach

  1. Do the exact version first, because it is affordable at this cardinality: a ring of 300 one-second counters per tenant, advanced lazily, is 1,200 bytes of counters per tenant and roughly 60 to 90 MB for 50,000 tenants with overhead. Carry a running total and subtract the bucket you overwrite so a window read is O(1) rather than 300 adds.
  2. Extract the top 50 with a size-k min-heap over the tenant sums: O(d log k) for d tenants, against O(d log d) to sort them all. Maintaining the heap continuously instead of on query requires a tenant-to-heap-index map, because incrementing a count already inside the heap means sifting from a known position, and without that map you rebuild the heap on every request.
  3. State the approximation precisely rather than gesturing at sketches. Misra-Gries with m counters retains every item whose true count exceeds N/(m+1), and each retained count underestimates the truth by at most N/(m+1). With m = 1,000 and N = 900,000 requests in the window the error is roughly 900 requests, which is fine for spotting a tenant sending 50,000 and useless for ranking two tenants 200 apart.
  4. Say what breaks when the window slides: Misra-Gries and Space-Saving are insert-only and cannot be decremented as records age out. The workable construction is one summary per sub-window, say ten seconds, with 30 summaries merged at query time, and the merged error is the sum of the per-summary errors, so the bound degrades linearly in the number of sub-windows.

Follow-up

  • The heaviest tenant is heavy because of one export job rather than user traffic. Should the limiter treat those as the same tenant?
  • Two tenants sit tied at the boundary of the top 50. Does your answer flap, and does the flapping matter?

Write a complex SQL query to extract and aggregate operational telemetry data across relational tables.

Medium · Technical & Software Fundamentals

Approach

  1. Name the grain you start from and join outward from it.
  2. Check whether any join is one-to-many before aggregating, or the sums inflate.
  3. Say which index the query would use, and what makes it unusable.
  4. Handle the rows that do not match: that is usually the actual question.

Follow-up

  • How does the query change if that join becomes one-to-many?
  • What happens to this when the table is ten times larger?

Keep soft-deleted accounts from blocking re-registration

Easy · soft delete · unique constraints · engine differences

app_user holds user_id, tenant_id, email CITEXT, password_hash (NULL for SSO principals), email_verified_at, auth_version, status ('invited','active','suspended','deactivated'), created_at, updated_at, deleted_at. Two live accounts for one address inside a tenant must be impossible, but an address freed by a soft delete must be reusable, and the same tenant may delete and re-register it repeatedly. Write the uniqueness DDL for PostgreSQL 16, then the equivalent for MySQL 8 where partial indexes do not exist, and say what each permits once three deleted rows already hold that address.

Approach

  1. Start from what is actually unique: not (tenant_id, email), but (tenant_id, email) among live rows. PostgreSQL says that directly — CREATE UNIQUE INDEX app_user_live_email ON app_user (tenant_id, email) WHERE deleted_at IS NULL. A full constraint over the same two columns burns the address permanently the first time someone deletes an account.
  2. Keep case-insensitivity in the type or the index, never in the application: CITEXT as given, or UNIQUE (tenant_id, lower(email)) as an expression index where the extension is unavailable. A case-sensitive unique column is exactly how two accounts for one human appear.
  3. For MySQL 8 the predicate has to move inside the key: add a discriminator column that is a constant 0 while the row is live and is set to user_id on delete, with UNIQUE (tenant_id, email, deleted_marker). Live rows share the constant and still collide; deleted rows differ from each other and stop colliding.
  4. State the NULL variant and its dependency: leaving the marker NULL for deleted rows also works, because a unique index treats NULLs as distinct — true in MySQL, and true in PostgreSQL only under the default NULLS DISTINCT, which PostgreSQL 15 lets you reverse. Check the polarity against the three existing deleted rows: constant-on-live is what preserves the collision you want, and reversing it silently admits duplicate live accounts.

Follow-up

  • A deleted account re-registers with the same address the next day. Do the old resource rows follow the new user_id, and how does the API keep the two principals apart?
  • How do you honour an erasure request while resource_revision.actor_user_id still references this table?

Explain Object-Oriented Programming (OOP) concepts based on a provided UML class diagram.

Medium · Technical & Software Fundamentals

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. Work from the requirement backwards to the design.

Follow-up

  • What assumption would you test first?
  • How would you know your answer was wrong?

How do you design software to maintain system stability during sensor signal dropouts or hardware faults?

Medium · Technical & Software Fundamentals

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. Work from the requirement backwards to the design.

Follow-up

  • What assumption would you test first?
  • How would you know your answer was wrong?

Describe the basic refrigeration cycle and explain how software controls expansion valves and compressors.

Medium · HVAC & Domain Integration

Approach

  1. Say who the caller is and what they do when the call fails halfway.
  2. Define the identity of a request so a retry cannot double-apply it.
  3. Separate accepted, pending, failed and confirmed; they are different facts.
  4. Design the error taxonomy before the success shape; callers branch on it.

Follow-up

  • What happens if the caller retries after a timeout?
  • How does a client discover it is on an old version of this contract?

How would you design a software feedback loop to regulate temperature and airflow in a commercial unit?

Medium · HVAC & Domain Integration

Approach

  1. Fix the scope first: who calls this, how often, and what they do when it fails.
  2. Name the read and write paths separately; they rarely have the same bottleneck.
  3. Choose a partition key and say what query it makes expensive.
  4. State the consistency you need, and where you are willing to be stale.

Follow-up

  • What breaks first when traffic grows ten times?
  • How does this behave when that dependency is down for an hour?

What factors count toward calculating heat load and deciding unit positioning for optimal climate control?

Medium · HVAC & Domain Integration

Approach

  1. Say who the caller is and what they do when the call fails halfway.
  2. Define the identity of a request so a retry cannot double-apply it.
  3. Separate accepted, pending, failed and confirmed; they are different facts.
  4. Design the error taxonomy before the success shape; callers branch on it.

Follow-up

  • What happens if the caller retries after a timeout?
  • How does a client discover it is on an old version of this contract?

How do microcontrollers read data from digital and analog sensors like relays and thermistors?

Medium · HVAC & Domain Integration

Approach

  1. Say who the caller is and what they do when the call fails halfway.
  2. Define the identity of a request so a retry cannot double-apply it.
  3. Separate accepted, pending, failed and confirmed; they are different facts.
  4. Design the error taxonomy before the success shape; callers branch on it.

Follow-up

  • What happens if the caller retries after a timeout?
  • How does a client discover it is on an old version of this contract?

Walk us through how you would architect a control application for a screw compressor or chiller unit.

Medium · HVAC & Domain Integration

Approach

  1. Fix the scope first: who calls this, how often, and what they do when it fails.
  2. Name the read and write paths separately; they rarely have the same bottleneck.
  3. Choose a partition key and say what query it makes expensive.
  4. State the consistency you need, and where you are willing to be stale.

Follow-up

  • What breaks first when traffic grows ten times?
  • How does this behave when that dependency is down for an hour?

How would you design an end-to-end telemetry system that streams diagnostic data from thousands of connected H

Medium · Problem-Solving & System Design

How would you design an end-to-end telemetry system that streams diagnostic data from thousands of connected HVAC units to the cloud?

Approach

  1. Fix the scope first: who calls this, how often, and what they do when it fails.
  2. Name the read and write paths separately; they rarely have the same bottleneck.
  3. Choose a partition key and say what query it makes expensive.
  4. State the consistency you need, and where you are willing to be stale.

Follow-up

  • What breaks first when traffic grows ten times?
  • How does this behave when that dependency is down for an hour?

How do you optimize database queries when processing large volumes of marketing or performance analytics?

Medium · Problem-Solving & System Design

Approach

  1. Fix the scope first: who calls this, how often, and what they do when it fails.
  2. Name the read and write paths separately; they rarely have the same bottleneck.
  3. Choose a partition key and say what query it makes expensive.
  4. State the consistency you need, and where you are willing to be stale.

Follow-up

  • What breaks first when traffic grows ten times?
  • How does this behave when that dependency is down for an hour?

How do you approach designing system interfaces when working with incomplete software requirements?

Medium · Problem-Solving & System Design

Approach

  1. Fix the scope first: who calls this, how often, and what they do when it fails.
  2. Name the read and write paths separately; they rarely have the same bottleneck.
  3. Choose a partition key and say what query it makes expensive.
  4. State the consistency you need, and where you are willing to be stale.

Follow-up

  • What breaks first when traffic grows ten times?
  • How does this behave when that dependency is down for an hour?

Describe how you perform component selection and system balancing for an integrated hardware-software platform

Medium · Problem-Solving & System Design

Describe how you perform component selection and system balancing for an integrated hardware-software platform.

Approach

  1. Say who the caller is and what they do when the call fails halfway.
  2. Define the identity of a request so a retry cannot double-apply it.
  3. Separate accepted, pending, failed and confirmed; they are different facts.
  4. Design the error taxonomy before the success shape; callers branch on it.

Follow-up

  • What happens if the caller retries after a timeout?
  • How does a client discover it is on an old version of this contract?

Walk through your step-by-step process for debugging a critical intermittent issue in a production control sys

Medium · Problem-Solving & System Design

Walk through your step-by-step process for debugging a critical intermittent issue in a production control system.

Approach

  1. Establish what changed and when, before forming any theory.
  2. Pick a bisection that eliminates candidates whichever way it turns out.
  3. Check the instrumentation before believing the symptom.
  4. Separate the trigger from the cause; the deploy is rarely the bug.

Follow-up

  • What would you look at first, and what would it rule out?
  • How would you tell a cause from a coincidence here?

Suggested practice checklist

Built from the rounds and topics Daikin candidates report.

Day 1 — Map the Daikin loop

  • Write out the reported sequence: Phone Screening, Technical Interviews, Behavioral Interviews, Stakeholder Engagement.
  • For each round, write one sentence on what it is judging, from the description above, and mark the one you are least ready for.

Deliverable: A one-page map of the 4 reported rounds, with the weakest marked.

Day 2 — Work Software Engineering Fundamentals

  • Spend the session on Software Engineering Fundamentals, which Daikin candidates report being tested on.
  • Write one worked example in Software Engineering Fundamentals and time yourself on it.

Deliverable: One timed worked example in Software Engineering Fundamentals.

Day 3 — Work Technical Interview Preparation

  • Spend the session on Technical Interview Preparation, which Daikin candidates report being tested on.
  • Write one worked example in Technical Interview Preparation and time yourself on it.

Deliverable: One timed worked example in Technical Interview Preparation.

Day 4 — Work Manufacturing Process Knowledge (Domain)

  • Spend the session on Manufacturing Process Knowledge (Domain), which Daikin candidates report being tested on.
  • Write one worked example in Manufacturing Process Knowledge (Domain) and time yourself on it.

Deliverable: One timed worked example in Manufacturing Process Knowledge (Domain).

Day 5 — Answer out loud: Technical & Software Fundamentals

  • Answer aloud, timed: Explain Object-Oriented Programming (OOP) concepts based on a provided UML class diagram.
  • Answer aloud, timed: How do you handle memory management and pointers in C/C++ when developing resource-constrained software?

Deliverable: Spoken answers to 2 reported Technical & Software Fundamentals question(s), under time.

Day 6 — Answer out loud: HVAC & Domain Integration

  • Answer aloud, timed: Describe the basic refrigeration cycle and explain how software controls expansion valves and compressors.
  • Answer aloud, timed: How would you design a software feedback loop to regulate temperature and airflow in a commercial unit?

Deliverable: Spoken answers to 2 reported HVAC & Domain Integration question(s), under time.

Day 7 — Answer out loud: Problem-Solving & System Design

  • Answer aloud, timed: How would you design an end-to-end telemetry system that streams diagnostic data from thousands of connected HVAC units to the cloud?
  • Answer aloud, timed: Walk through your step-by-step process for debugging a critical intermittent issue in a production control system.

Deliverable: Spoken answers to 2 reported Problem-Solving & System Design question(s), under time.

Behavioural preparation

Behavioural rounds judge the decision you made and what it cost.

Describe a situation where you had to work directly with a manufacturing or production crew to resolve an issu

Medium · Behavioral & Team Collaboration

Describe a situation where you had to work directly with a manufacturing or production crew to resolve an issue.

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

How do you respond when a project timeline is compressed or critical deadlines are running late?

Medium · Behavioral & Team Collaboration

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

Give an example of a time you had to explain a complex technical concept to a non-technical stakeholder.

Medium · Behavioral & Team Collaboration

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

How do you handle disagreements with team members or senior leadership regarding system architecture?

Medium · Behavioral & Team Collaboration

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

Describe yourself in three words and explain why you chose to apply to Daikin.

Medium · Behavioral & Team Collaboration

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?