PACCAR MX 13 Sensor Locations Diagram: 2026 HVAC Guide
The PACCAR MX-13 HVAC sensor network includes the high-side refrigerant pressure sensor located on the liquid line near the condenser, the evaporator freeze sensor mounted inside the HVAC unit housing near the blower motor, and the ambient air sensor behind the front grille. Sensors feed 5V reference signals directly to the CECU.
📌 Key Takeaways
- High-pressure refrigerant sensor operates on a 5V DC reference signal, outputting 0.5V to 4.5V based on pressure.
- Evaporator temperature sensor mounts directly inside the HVAC box next to the blower motor to prevent coil icing.
- A/C pressure sensor connector pinout: Pin A (5V Ref), Pin B (Ground), Pin C (Signal output to CECU).
- Corroded wiring at the front bumper ambient air sensor frequently prevents A/C compressor clutch engagement.
- Use PACCAR DAVIE 4 diagnostic software to re-calibrate pressure sensor fault thresholds after replacing components.
Navigating the complete diagram Paccar MX 13 sensor locations is essential for diagnosing engine performance faults and climate control malfunctions on Kenworth and Peterbilt heavy-duty trucks. The Paccar MX-13 engine utilizes a sophisticated network of electronic sensors to manage fuel injection, exhaust emissions, and engine cooling, while simultaneously interfacing with the vehicle heating, ventilation, and air conditioning (HVAC) system. Whether you are pinpointing a faulty refrigerant pressure sensor near the condenser or replacing an intake manifold temperature sensor behind the fuel module, understanding exact spatial coordinates, wiring pinouts, and physical reference landmarks will significantly reduce diagnostic downtime on EPA10, EPA13, and GH17/GH21 engine platforms.
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Diagram Paccar Mx 13 Sensor Locations and HVAC Component Layout
As shown in the diagram above, locating sensors on the Paccar MX-13 requires identifying major engine casting features and HVAC housing assemblies. Sensor placement is engineered around the left-side fuel module, the right-side turbocharging system, and the cab-mounted air handler unit.
The Crankshaft Position (CKP) sensor is mounted on the lower left-rear section of the engine flywheel housing, positioned directly above the starter motor frame. It aligns with the internal flywheel target ring to record engine RPM and timing reference. Directly above it, near the top rear face of the cylinder head on the driver side, sits the Camshaft Position (CMP) sensor. It is secured into the aluminum rear housing behind the upper valve cover seam.
For climate control integration, the Engine Coolant Temperature (ECT) sensor is installed into the front left-hand side of the cylinder head casting, situated immediately behind the primary thermostat housing assembly. This sensor monitors engine coolant thermal output as it circulates through the primary heat exchanger system and cab heater core. Faulty ECT signals disrupt both engine fan engagement and cab air handler thermal control.
The high-pressure refrigerant pressure sensor is located externally on the high-pressure liquid line between the condenser outlet and the receiver-drier assembly along the right frame rail. This sensor monitors system operating pressure, sending analog voltage signals to the engine ECU to command the AC compressor clutch on or off. Inside the cab enclosure, the evaporator temperature sensor is inserted directly between the cooling fins of the evaporator core inside the HVAC air handler plenum on the passenger floorboard. Adjacent to this core, inside the main return duct housing, you will find the blower motor control resistor and return duct air temperature probe, which together control cabin climate conditioning and core freeze prevention.
Paccar MX-13 Engine and Climate Control Sensor Specifications
Refer to the technical data table below for precise placement landmarks, wire color identifications, and factory torque specifications when servicing components identified in the diagram Paccar MX 13 sensor locations layout.
| Sensor / Component Name | Physical Location & Landmarks | Wire Colors & Pinout Specs | Factory Torque Spec |
|---|---|---|---|
| Crankshaft Position (CKP) | Left-rear flywheel housing, 3 inches above starter flange | Pin 1: Yellow, Pin 2: Green (Shielded twisted pair) | 8 Nm (71 in-lbs) |
| Camshaft Position (CMP) | Upper driver-side rear cylinder head, behind valve cover end panel | Pin 1: White, Pin 2: Brown (5V pulse reference) | 8 Nm (71 in-lbs) |
| Engine Coolant Temp (ECT) | Front left cylinder head, rearward of thermostat housing | Pin A: Blue/Red, Pin B: Black/Ground | 22 Nm (16 ft-lbs) |
| Refrigerant High-Pressure Sensor | High-pressure liquid line near right-side condenser bracket | Pin A: 5V Red, Pin B: Signal Blue, Pin C: Ground Black | 11 Nm (97 in-lbs) |
| Evaporator Core Temp Sensor | Inside passenger HVAC air handler, inserted into evaporator fin center | 2-Wire harness: Green/Yellow & Black (NTC thermistor) | Hand-tight clip retainer |
| Manifold Absolute Pressure (MAP/IAT) | Center intake manifold log, driver side above fuel module | 4-Pin connector: 5V Ref, Signal, Temp, Return Ground | 10 Nm (88 in-lbs) |
How to Locate and Service Paccar Mx 13 Sensors Step-by-Step
When executing maintenance or sensor replacements based on the diagram Paccar MX 13 sensor locations, follow a systematic process to avoid harness damage, improper readings, or thread damage in aluminum engine castings.
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Always verify system voltage using a digital multimeter before replacing any sensor. Sensor 5.0V reference lines must remain within 4.85V to 5.15V DC with key switch ON. Sensor mounting bolts require low-profile metric sockets to prevent rounding head fasteners in tight engine bays.
Step 1: Isolate and Access the Target Location
Position the vehicle on level ground, set the parking brakes, and disconnect the main chassis battery disconnect switch. For engine-mounted sensors such as the MAP or ECT sensors on the driver side, tilt the hood fully forward and remove the driver-side lower inner fender splash shield. For HVAC air handler components, remove the lower passenger dash panel cover to access the blower motor and evaporator housing ductwork.
Step 2: Inspect Wiring Harness Integrity
Before unbolting the sensor, inspect the electrical connector for lock tab damage, green corrosion, or oil intrusion. Unclip the locking tab and pull the harness straight off. Use back-probe pins to measure signal voltages and reference grounds. Consult our Kenworth cab climate control module wiring documentation for detailed pinout schematic paths.
Step 3: Remove Component and Clean Mounting Surface
Use a deep-well socket or line wrench to unscrew the target sensor. For sensors sealed with O-rings (such as the MAP sensor or high-pressure refrigerant switch), carefully discard the old seal. Thoroughly clean the mounting bore or threaded port with a lint-free cloth and electrical contact cleaner to prevent debris from entering the intake tract, coolant gallery, or refrigerant lines.
Step 4: Install New Sensor to Torque Specification
Apply thread sealant only if specified by OEM manuals (e.g., NPT coolant sensors). Thread the replacement sensor by hand to avoid cross-threading into engine aluminum ports. Torque the sensor to manufacturer specifications using a calibrated torque wrench. Reattach the electrical connector until the locking clip snaps firmly into position.
After replacing engine management or emissions-related sensors on EPA13 and GH17 Paccar MX-13 engines, clear inactive fault codes and perform a sensor calibration reset using DAVIE4 diagnostic software to allow the Engine Electronic Control Unit (P300 or PCI module) to re-learn baseline resistance values.
Diagnostic Procedures for Paccar Mx 13 Climate and Sensor Faults
Diagnosing sensor faults on a Paccar MX-13 requires separating true sensor electrical failure from harness chaffing, low refrigerant charge, or mechanical cooling problems. Fault codes related to the high-pressure switch or evaporator temperature probe directly impact AC compressor clutch operation.
If the AC compressor clutch fails to engage, start by checking the refrigerant pressure sensor signal line voltage on the right frame rail. The ECU monitors line pressure to ensure system safety. If pressure drops below 30 PSI or exceeds 425 PSI, the ECM locks out the AC compressor relay. Measure the signal wire voltage: at static room temperature (70°F / 21°C) with a fully charged system, the sensor should output approximately 1.2V to 1.5V DC. If signal voltage reads 0.0V or 5.0V continuously, check for harness chafing against the front engine crossmember or front cab mounts.
Similarly, an erratic reading from the evaporator temperature sensor will cause the HVAC air handler to misread core temperatures. If the sensor fails shorted, the system falsely reports an iced evaporator core, disabling the compressor clutch indefinitely. If it fails open, the compressor runs continuously, causing the evaporator core to freeze solid and blocking cabin airflow through the return duct. Check our comprehensive heavy-duty AC compressor troubleshooting guide for systematic pressure diagnosis steps.
Never attempt to service or remove the high-pressure refrigerant sensor without verifying if the mounting fitting contains an internal Schrader valve stem. Unthreading a non-Schrader pressure port on an active R134a or R1234yf system will result in explosive refrigerant discharge and severe personal injury.
Engine-side sensor faults often manifest as derate conditions. A skewed Engine Coolant Temperature (ECT) sensor reading can cause the ECU to command maximum fan clutch engagement while simultaneously limiting engine torque. Cross-reference live ECT data against actual engine housing thermal images using an infrared thermometer. If live data shows 220°F (104°C) but the thermostat housing measures 180°F (82°C), inspect the ECT harness plug for water ingress or replace the sensor unit. Additional fault code resolution details are accessible in our Paccar MX-13 fault code diagnostic library.
Diagram Paccar Mx 13 Sensor Locations Frequently Asked Questions
Where is the high-pressure refrigerant sensor located on a Paccar MX-13 chassis?
The high-pressure refrigerant sensor is located on the liquid refrigerant line along the front right-hand (passenger side) frame rail, between the condenser outlet fitting and the receiver-drier assembly. It is positioned near the front engine radiator support framework for easy accessibility during AC system service.
How do you access the evaporator temperature sensor inside the cab air handler?
Accessing the evaporator temperature sensor requires removing the lower passenger-side dash trim panel and glovebox assembly. The sensor is mounted directly into the side plenum of the main plastic HVAC air handler housing. It features a two-wire probe inserted straight into the aluminum fins of the evaporator core.
What are the primary symptoms of a failing Paccar MX-13 coolant temperature sensor?
A failing ECT sensor on a Paccar MX-13 engine typically triggers engine fault codes P0115, P0117, or P0118. Symptoms include the cooling fan running continuously at high RPM, inaccurate dashboard temperature gauge readings, erratic cab heater output from the HVAC heat exchanger, and potential engine power derate forced by the engine protection system.
Why does the A/C compressor fail to engage even when refrigerant pressure is correct?
If static refrigerant pressure is normal but the AC compressor clutch will not energize, the Paccar PCI engine ECU may be receiving an out-of-range signal from either the ambient air temperature sensor, the evaporator thermistor (indicating a false frozen core condition), or the high-pressure cutout switch. Additionally, engine sensor faults like an overheating ECT signal will cause the ECU to disengage the AC compressor clutch to reduce engine thermal load.
How do sensor locations differ between EPA13 and GH17 or GH21 Paccar MX-13 models?
While basic core engine sensor positions (CKP, CMP, ECT) remain in similar locations across generations, GH17 and GH21 emissions-compliant engines feature restructured intake manifold assemblies and updated exhaust aftertreatment architecture. The intake manifold air temperature and pressure sensors (MAP/IAT) were moved slightly higher on the intake plenum log to accommodate updated EGR mixing pipe geometry. Always cross-reference your specific engine serial number (ESN) with official factory schematics prior to servicing.
