This collection of HVAC technician interview questions and answers is built from real written-test papers used for commercial HVAC roles in the UAE — the kind of buildings where you’ll find chillers, AHUs, and cooling towers running: airports, metro stations, hospitals, and shopping malls. Every answer here is explained in plain English, not just the correct option, so you actually understand why it’s correct.
This is Part 1 of the series. Each part covers a fresh set of questions with full explanations, diagrams where they help, and links to free calculators on Learn HVAC Pro so you can practice the numbers yourself. If you’re getting ready for real HVAC technician interview questions in the Gulf, working through an actual written-test paper like this, question by question, is the fastest way to walk in prepared.
Table of Contents
Section A: DX (Direct Expansion) AC System
Q1. In a refrigeration system, the thermostatic expansion valve (TXV) is connected between the:
a. Compressor and Condenser
b. Condenser and Evaporator
c. Evaporator and Compressor
Correct answer: b — Condenser and Evaporator
Here’s the easy way to remember this. Refrigerant travels around a loop in one direction:
Compressor → Condenser → [Receiver] → TXV → Evaporator → back to Compressor
(high pressure) (low pressure)
The TXV’s whole job is to drop the pressure of the refrigerant right before it enters the evaporator. It sits in the liquid line, after the condenser (where the refrigerant has already turned into a high-pressure liquid) and just before the evaporator (where it needs to be a low-pressure liquid so it can boil off and absorb heat from the room).
If you moved the TXV anywhere else in the loop, the system physically wouldn’t work — this is why it’s always found in exactly this spot. This TXV-location question is one of the most frequently repeated HVAC technician interview questions on UAE written tests, so make sure you can explain the reasoning, not just recite the letter.
Once you know your system’s tonnage, you can size the rest of the components correctly using the AC Tonnage Calculator.
Q2. 10 Tons of refrigeration is equal to how many BTU/hr?
a. 12,000
b. 24,000
c. 61,000
d. None of these
Correct answer: d — None of these
This one catches people out because it looks like a simple conversion question, but none of the three numbers given are actually correct — so you have to know the real math to spot it.
The standard conversion is: 1 Ton of refrigeration = 12,000 BTU/hr
So for 10 Tons: 10 × 12,000 = 120,000 BTU/hr
None of options a, b, or c equal 120,000 — so the honest answer is (d). Trick questions like this show up often in HVAC technician interview questions because employers want to see whether you actually calculate, or just guess “the answer is usually b or c.”
You can check any BTU/Ton/kW conversion instantly with the HVAC Unit Converter — useful for double-checking yourself during an actual written test if you’re allowed a phone, and definitely useful on the job.
Q3. The condenser in the vapor-compression cycle contains:
a. Saturated High-Pressure Vapor
b. Saturated High-Pressure Liquid
c. A mixture of Liquid and Vapor
d. Saturated Low-Pressure Liquid
Correct answer: c — A mixture of Liquid and Vapor
Refrigerant doesn’t change from vapor to liquid instantly inside the condenser — it happens gradually as heat is rejected to the outside air (or condenser water). Here’s what actually happens as refrigerant passes through the coil:
Compressor discharge → [Superheated Vapor] → [Mixture of Liquid + Vapor] → [Saturated Liquid] → Liquid line
(condenser inlet) (most of the coil) (condenser outlet)
For most of the physical length of the condenser coil, the refrigerant is sitting at its saturation temperature and existing as a two-phase mixture — some of it still vapor, some already condensed to liquid. That’s why “a mixture of liquid and vapor” is the textbook-correct description of what’s inside the condenser overall, even though the very start and end points are different. Diagram-based questions like this are common in HVAC technician interview questions because they test whether you understand the cycle, not just memorized definitions.
Q4. Knocking, rattling, or heavy hissing in the compressor at start-up is an indication of:
a. Undercharge
b. Liquid Refrigerant in Compressor
c. Overcharge
d. High Superheat
Correct answer: b — Liquid Refrigerant in Compressor
This is a classic field problem called liquid slugging or liquid floodback. A compressor is built to compress gas, not liquid — liquid doesn’t compress.
If liquid refrigerant makes it back to the compressor (usually because of low superheat, a flooded evaporator, or refrigerant migrating back during the off-cycle), the compressor tries to squeeze it anyway. That’s what causes the loud knocking and rattling noise, and it can physically damage the valves and bearings inside very quickly.
This is exactly why superheat readings matter so much on the job — checking it properly tells you whether the evaporator is being fed correctly, and it’s a scenario examiners like to test in HVAC technician interview questions because it separates memorized theory from real fault-finding. You can practice reading and diagnosing real superheat values using the Superheat & Subcooling Calculator.
Q5. Which of the following refrigerants is ozone-friendly?
a. R-11
b. R-12
c. R-22
d. R-410A
Correct answer: d — R-410A
R-11, R-12, and R-22 all contain chlorine (they’re CFCs or HCFCs), and chlorine is what damages the ozone layer. R-410A is an HFC blend — it contains no chlorine, so its Ozone Depletion Potential (ODP) is zero.
This is also why R-22 has been phased out globally under the EPA’s ozone-depleting substance phaseout schedule, and R-410A became the standard replacement in most split and package AC units before newer low-GWP refrigerants like R-32 started replacing it too. Questions like this show up often in HVAC technician interview questions because refrigerant regulations keep changing, and employers want to know you’re up to date.
Q6. Unit Conversions
| Convert | Answer | How |
|---|---|---|
| 212°F to °C | 100°C | This is the boiling point of water at sea level |
| 32°F to °C | 0°C | This is the freezing point of water |
| 48,000 BTU/hr to TR | 4 TR | 48,000 ÷ 12,000 = 4 |
| 36 MBH to TR | 3 TR | MBH means “thousand BTU/hr,” so 36 MBH = 36,000 BTU/hr → 36,000 ÷ 12,000 = 3 |
| 60 MBH to BTU/hr | 60,000 BTU/hr | 60 MBH = 60 × 1,000 |
For any of these on a real test or on the job, the HVAC Unit Converter handles BTU, Ton, kW, °F, °C, PSI, Bar and CFM conversions instantly. Unit-conversion tables like this one appear in almost every set of HVAC technician interview questions, so it’s worth memorizing the core factors rather than converting from scratch each time.
Q7. What is the expansion of the abbreviations VRF and VRV? Explain the VRF system with a simple diagram.
VRF = Variable Refrigerant Flow
VRV = Variable Refrigerant Volume
These two terms mean the same thing in practice — VRV is actually a trademarked name owned by Daikin, while VRF is the generic industry term everyone else uses (Mitsubishi, LG, Gree, etc. all call their systems VRF). Don’t overthink the difference in an interview; just know they describe the same technology.
How it works: one outdoor unit supplies refrigerant to many indoor units at once, and each indoor unit can independently control how much refrigerant it needs using its own electronic expansion valve (EEV). This means one indoor unit can be cooling a room while another connected to the same outdoor unit is heating a different room — something a normal split system can’t do.
+------------+
| OUTDOOR |
| UNIT |
+-----+------+
| (refrigerant piping, branches out)
+-----------+-----------+
| | |
+-----+-----++----+------++----+------+
| Indoor 1 || Indoor 2 || Indoor 3 |
| (Room A) || (Room B) || (Room C) |
+-----------++-----------++-----------+
each has its own EEV - controls its own flow independently
This diagram is drawn this way because that’s exactly the physical layout of a VRF installation: one refrigerant source, many independent branches. VRF/VRV system diagrams like this are a favorite in HVAC technician interview questions because they separate candidates who understand the layout from those who’ve only memorized the acronym. That’s the entire point of the technology — flexibility to control temperature room-by-room, from a single outdoor condensing unit, which is why VRF systems are common in hotels, office towers, and mixed-use buildings across the UAE.
Section B: Air Handling & Fan Coil Systems
Q8. A typical fan coil unit valve package is a simplified way to control water flow through the coil while keeping total system flow constant. Explain how the supply valve, actuated valve, and bypass valve work together.
A fan coil unit (FCU) needs chilled water flowing through its coil to cool the air passing over it. But the amount of water it needs changes constantly as the room’s cooling demand changes. The problem is: if you simply throttle a valve to reduce flow into one FCU, it changes the water pressure for every other FCU on the same chilled water loop — which causes control problems across the whole building. This valve-package question is another one that shows up regularly in HVAC technician interview questions for building-services roles.
The fix is a valve package with a bypass line:
Supply Valve Coil Actuated Valve
Supply ------[ ]----------+---[COIL]---+------------[ ]----------To Coil
Line | |
| |
+----[ ]-----+
Bypass Valve
(opens when coil valve closes)
Here’s why it’s drawn like this: the actuated valve modulates how much water goes through the coil based on the room thermostat’s demand. As that valve closes (less cooling needed), the bypass valve opens automatically to let water skip the coil and flow straight back to the return line instead. This keeps the total flow rate through that branch nearly constant no matter what the coil valve is doing — which keeps pressure stable for every other FCU sharing the same pumped loop.
This bypass arrangement is very common on older constant-flow secondary chilled water systems, and it’s one of the first things a technician should check when a whole floor of FCUs starts acting up together — a bypass valve stuck open (or the actuated valve stuck closed) is a classic root cause.
Q9. Explain the relationship between speed and the diameter of pulleys.
This comes up constantly in real fan and motor troubleshooting, and the relationship is simple and fixed:
Motor RPM × Motor Pulley Diameter = Fan RPM × Fan Pulley Diameter
In other words, speed and diameter are inversely related on a belt-driven system — make one pulley bigger, and the shaft it’s on turns slower; make it smaller, and it turns faster. This is why changing a fan’s speed on site (to increase or reduce airflow) is often done simply by swapping the motor or fan pulley for a different diameter, rather than replacing the whole motor.
You can calculate exact pulley ratios, belt length, and resulting fan RPM using the Motor, Belt, Pulley & Bearing Calculator — the same formula tested against real job-site numbers, and this exact relationship shows up repeatedly across HVAC technician interview questions on motor and fan sections.
Q10. What is the difference between a bypass VAV and a pressure-dependent VAV? Illustrate with a diagram.
These two terms describe different ways a VAV (Variable Air Volume) box can be controlled, and they’re often confused — and questions comparing them are common in HVAC technician interview questions for commercial building roles:
Bypass VAV: The AHU fan keeps blowing a constant volume of air at all times. When a room needs less cooling, the VAV box doesn’t actually reduce how much air reaches that room — instead, it dumps the extra, unneeded air into the ceiling return plenum through a bypass damper. The AHU itself never sees a reduced load — it’s always working at full output. This wastes energy but is simple and cheap, so you’ll still find it in some older UAE buildings.
Pressure-dependent VAV: The damper inside the VAV box opens or closes purely based on the room thermostat signal — but it has no airflow sensor of its own. So if the duct static pressure elsewhere in the system changes (say, another VAV box on the same duct closes), the actual airflow through this box changes too, even though its damper position didn’t move.
This is different from a pressure-independent VAV box, which has a built-in flow sensor and a local controller that automatically corrects the damper position to hold a set CFM regardless of what else is happening in the ductwork — pressure-independent is the standard in modern commercial UAE buildings.
BYPASS VAV PRESSURE-DEPENDENT VAV
AHU --> Duct --+--> Room AHU --> Duct -->[Damper]--> Room
| (opens/closes only on
+--> Bypass --> Return thermostat signal -
(dumps excess air no airflow feedback)
back to return, AHU
output never changes)
The key thing to remember for an interview: bypass VAV never actually changes what the AHU is doing — it just reroutes air. Pressure-dependent VAV does respond to the room, but without checking what airflow it’s actually delivering — which is exactly the gap that pressure-independent VAV boxes were designed to close.
More HVAC Technician Interview Questions Coming in This Series
This series is being built up part by part, working through real HVAC technician interview questions from actual written-test papers, question by question, with every answer checked against real formulas and standards rather than guessed. Part 2 will move into chilled water systems, cooling towers, and AHU components in more depth — the kind of questions commonly asked for HVAC roles in large UAE facilities like airports, hospitals, and metro stations.
Bookmark this page if you’re actively preparing — new HVAC technician interview questions and answers get added to this series regularly, and every explanation here is written by a working HVAC supervisor, not copied from a generic study guide.
Want to know more about who’s behind these breakdowns? Read the About Learn HVAC Pro page — 10 years of real field experience in Dubai and Sharjah, not textbook theory.