I really appreciate how honest and efficient this company is. They identified the problem quickly and fixed it without unnecessary charges. I would definitely recommend them!
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Matthew Lim
Aircon Thermistor Repair in Singapore
Thermistors are temperature sensors that tell the PCB what the room, coil, and pipe temperatures are. When a sensor drifts, shorts, or fails, the unit misreads conditions and behaves erratically — overcooling, undercooling, freezing up, or refusing to start. We test each sensor to confirm which one has failed.
How we approach thermistor issues
Test before replacing
We measure sensor resistance and compare to the expected curve. A sensor is only replaced when the reading confirms it has failed or drifted out of range.
Check wiring too
A loose connector or damaged wire causes the same symptoms as a dead sensor. We check the full signal path before ordering a new part.
Correct rated replacement
Thermistors are rated to a specific resistance curve. We match the replacement to the unit model — a generic sensor with the wrong curve causes the same problems.
Signs of a thermistor problem
Sensor faults cause the unit to misread temperature. The symptoms vary depending on which sensor has failed and how it has failed.
- Unit cools the room well past the set temperature and does not stop
- Unit shuts off before the room reaches the set temperature
- Error code pointing to a sensor fault or temperature reading error
- Ice forming on the evaporator coil even after cleaning and gas check
- Room temperature display reads an obviously wrong number
- Unit starts and stops repeatedly in short cycles
How thermistor diagnosis works
Most units have two to four thermistors — room sensor, indoor coil sensor, outdoor coil sensor, and sometimes a pipe sensor. We test each one to find the faulty part.
1. Error code check
Many units flag a specific sensor fault code. We read the code first — it often points directly to the sensor that has failed.
2. Resistance measurement
We measure the resistance of each thermistor at the current temperature and compare it to the expected value. A drifted or open reading confirms the sensor is faulty.
3. Wiring and connector check
A loose connector or damaged wire can mimic a sensor fault. We check the wiring path and connector pins before replacing the sensor itself.
4. Sensor replacement
The faulty sensor is replaced with the correct rated thermistor for the unit model. We confirm the replacement reads correctly before reassembling.
5. Test run and confirmation
The unit is run through a cooling cycle to confirm the PCB reads the new sensor correctly and the system reaches and holds the set temperature normally.
Pricing
Thermistors are inexpensive parts. Most of the cost is in the diagnostic time to confirm which sensor has failed and sourcing the correct replacement.
- Diagnostic visit includes error code reading and sensor testing
- Sensor replacement is usually low-cost compared to other component repairs
- Some units use brand-specific sensors that may need ordering
- No work starts until you agree to the quote
Booking and visit timing
Diagnosis and replacement are usually done in a single visit. Brand-specific sensors may need ordering.
- Diagnostic and replacement typically completed in one visit
- Common thermistor types are carried in stock
- Brand-specific or less common sensors may need a follow-up for sourcing
- We confirm timing once we identify the sensor model needed
Sensors we check
Each thermistor tells the PCB a different temperature reading. The number and type of sensors depends on the unit model.
- Room air sensor — measures return air temperature for set-point control
- Indoor coil sensor — monitors evaporator temperature to prevent freezing
- Outdoor coil sensor — monitors condenser temperature for defrost and protection
- Pipe sensor — measures refrigerant pipe temperature on some models
- Discharge sensor — monitors compressor discharge temperature on inverter units
Common thermistor faults
These are the sensor-related faults we see most often in residential split systems.
- Drifted resistance — sensor reads high or low, causing the unit to overcool or undercool
- Open circuit — sensor wire broken internally, PCB reads no signal and throws an error
- Short circuit — sensor resistance drops to near zero, PCB misreads temperature
- Loose connector — intermittent contact causes erratic temperature readings
- Corrosion on sensor tip — moisture damage on the coil sensor over time
- Wrong replacement — previous repair used the wrong rated sensor for the unit
When the problem is not the sensor
Sensor-like symptoms can also come from other faults. We check the sensor first, but if it tests normal, the issue is elsewhere.
- PCB fault — the board misreads a healthy sensor signal
- Wiring damage — broken wire between the sensor and the PCB
- Expansion valve fault — coil temperature issues caused by metering, not sensing
- Low gas — coil icing caused by refrigerant undercharge, not a sensor misread
What customers say
Highly professional and efficient service! The technicians arrived on time, performed a thorough cleaning, and fixed my aircon issue. Honest pricing, no hidden charges.
I
Irwan Abu Samah
Initially engaged another company to look into the issue with our aircon but was quoted a much higher price. Snowflake clearly explained the issue and what needs to be done, and recommended possible solutions based on their expertise.
R
Rafidah B
Snowflake clearly explained the cause of the issue and what needs to be done, recommended possible solutions based on what is best for the customer.
S
SaifudinDxdin
Thermistor repair FAQ
Related reading
Unit behaving erratically or showing a sensor error?
Share the error code and symptoms. We will confirm whether a sensor check is the right next step.
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