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Audi S4 A/C Evaporator Temperature Sensors

Audi S4 A/c evaporator temperature sensors

Starting at $36.95, AutoBuffy stocks 2 A/C evaporator temperature sensors from URO and Standard Ignition. This sensor monitors evaporator core temperature and signals the A/C control module to cycle the compressor off before ice forms. When it fails, the evaporator can freeze solid or the compressor may run erratically, leaving your Audi S4 blowing warm or barely cool air.

Signs your Audi S4 needs a new A/C evaporator temperature sensor

  • A/C blows warm air after running normally for a few minutes, then partially recovers once ice melts
  • Reduced or no airflow from vents caused by a frozen evaporator core blocking the air path
  • Compressor clutch cycles on and off rapidly or stays off entirely even with A/C set to max
  • Frost or condensation visible on the evaporator housing or A/C drain tube under the dashboard
  • A/C-related fault codes stored in the HVAC or PCM module, such as an evaporator sensor circuit error
  • Musty or moldy odor from vents caused by standing water from repeated freeze-thaw cycles on the core

Which A/C evaporator temperature sensor should you buy for your Audi S4?

The main decision is whether to match OE sensor resistance and connector type or accept an aftermarket unit that approximates them. Fit and calibration matter here — a sensor with a slightly different thermistor curve will cause the same freeze-up or short-cycling problems you are trying to fix. Confirm the connector style and resistance specification before buying.

OE Replacement (aftermarket)
Best for
Daily drivers needing a reliable, cost-effective fix
What you get
Matched thermistor curve and connector; tested to OE resistance specs at a lower price than dealer parts
OEM / Dealer-Sourced Sensor
Best for
Vehicles under warranty or owners who want exact factory spec
What you get
Guaranteed connector fit, OE calibration, and manufacturer backing; highest upfront cost
Economy / Value Line
Best for
Older vehicles or short-term repairs where cost is the priority
What you get
Basic thermistor function at the lowest price; connector fit may require adapting; lifespan varies
Sensor + Pigtail Connector Kit
Best for
Vehicles with corroded or damaged connector housings
What you get
New sensor pre-wired to a fresh connector; eliminates a common failure point and ensures a clean electrical connection

A/c evaporator temperature sensors brands we stock for your Audi S4

URO
1 option · from $36.95
Standard Ignition
1 option · from $80.95

Replacing the A/C evaporator temperature sensor on a Audi S4

Easy⏱ 30–60 minutesOBD-II or HVAC-capable scan toolMultimeterTrim panel removal toolsFlathead screwdriver or small pickNeedle-nose pliers

On most vehicles the evaporator temperature sensor clips directly into the evaporator core fins through an access point behind the glove box or lower dash panel — refrigerant does not need to be discharged. Remove the trim panel, unplug the connector, pull the sensor free, seat the new one until it clicks, and reconnect the harness. Clear any stored fault codes with a scan tool and run the A/C through a full cycle to confirm the compressor cycles correctly and no freeze-up recurs.

Frequently asked questions

How much does it cost to replace A/C evaporator temperature sensors on a Audi S4?
The part itself starts at $36.95 at AutoBuffy. Total cost depends on whether a shop or dealership does the work — labor is usually minimal since the sensor clips into the evaporator housing without discharging the refrigerant system. Most independent shops charge under an hour of labor for sensor-only replacement.
Can a bad evaporator temperature sensor cause the A/C to stop working completely on a Audi S4?
Yes. If the sensor sends an out-of-range signal, the HVAC control module will shut the compressor down as a protection measure. The system reads the signal as a potential freeze or overload condition. Clearing the fault and installing a correctly calibrated sensor typically restores normal compressor operation.
Will a faulty evaporator temperature sensor throw a check engine or HVAC fault code on a Audi S4?
It often does. The HVAC or powertrain control module monitors the sensor's resistance signal and will log a circuit-range or rationality fault if the reading falls outside expected values. Scanning with an OBD-II or manufacturer-specific scan tool before replacing parts confirms whether the sensor or its wiring is the root cause.
Is it safe to drive or use the A/C on a Audi S4 with a bad evaporator temperature sensor?
Driving is safe, but continued A/C use risks freezing the evaporator core solid. A frozen core blocks airflow entirely and can force water past the drain tube onto the cabin floor. If the system keeps short-cycling or blowing warm, turning the A/C off until the sensor is replaced prevents secondary damage.
How do I know if it's the evaporator temperature sensor or something else causing freeze-up on my Audi S4?
Check for fault codes first. If the evaporator sensor circuit is flagged, measure the sensor's resistance with a multimeter and compare it to the specification for your system. A sensor reading open, shorted, or out of spec at ambient temperature confirms failure. Also inspect the cabin air filter and blower — low airflow from other causes can mimic a sensor problem.
How long does an A/C evaporator temperature sensor typically last on a Audi S4?
Most sensors last many years under normal use, but corrosion at the connector, exposure to moisture inside the evaporator housing, and heat cycling can shorten service life. Vehicles in high-humidity climates or those that use the A/C heavily year-round tend to see sensor issues sooner than those in drier conditions.

Shop a/c evaporator temperature sensors by year for the Audi S4

20082007200620052004200220012000

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A/c evaporator temperature sensors for other Audi models

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