Owner's Problem Description
The owner reports that the A/C unit in their Nissan Pickup truck receives no power. When the A/C is activated, there is no power supplied to the compressor. The owner has not performed any previous repairs on the A/C system. Currently, the truck does not have A/C functionality, which is affecting comfort during warm weather.
Professional Technical Analysis
For this Nissan Pickup, the lack of power to the A/C compressor can stem from several potential issues. The A/C system likely contains a refrigerant pressure switch that disables the compressor when the refrigerant levels are outside acceptable ranges. Given the reported low side pressure of 120 psi, it is essential to confirm if this reading is accurate and what the high side pressure would be. Normally, with the compressor off, the low side pressure should be approximately 80-100 psi, indicating adequate refrigerant in the system. Additionally, the compressor may not engage if there is an electrical issue, such as a blown fuse or a faulty A/C relay. Inspect the A/C fuse (typically located in the fuse box) for continuity; if blown, replace it with OEM P/N 24380-0C200, which costs around $5. If the fuse is intact, check the A/C relay, which also could be malfunctioning. The relay can usually be found in the engine compartment fuse box. Testing the relay with a multimeter for continuity is recommended. Voltage to the compressor should be approximately 12V when activated; use a multimeter to check for voltage at the compressor connector when the A/C is on. If no voltage is present, further investigation into the wiring harness and A/C control switch may be necessary. This systematic approach will help narrow down the root cause of the issue and establish whether it's a refrigerant level problem or an electrical fault.
Possible Causes
Most common causes (ordered by frequency):
- Refrigerant Pressure Switch Inaction: The refrigerant pressure switch may disable the A/C compressor due to low refrigerant levels or high pressure, causing it not to engage. The typical low side pressure range should be between 80-100 psi with the compressor off, indicating proper refrigerant levels. A reading of 120 psi on the low side could suggest a potential blockage or overcharge, requiring further inspection of the refrigerant system. - No power to compressor, low side pressure reading of 120 psi during inspection.
- A/C Fuse Failure: A blown fuse can interrupt power supply to the A/C compressor, preventing it from activating. Inspect the A/C fuse located in the fuse box for continuity. If the fuse is blown, replace it with OEM P/N 24380-0C200, which typically costs around $5. - Visual inspection of the fuse shows no continuity.
- A/C Relay Malfunction: The A/C relay may be faulty, preventing power from reaching the compressor. This relay can be tested for continuity and should be replaced if found defective. The relay is usually located in the engine compartment fuse box. - No activation signal to the compressor when A/C is turned on, relay tests show no continuity.
- Electrical Connection Issues: Loose or corroded electrical connectors can hinder the power supply to the A/C compressor. Inspect the wiring harness and connectors for signs of damage or corrosion. Ensure all connections are secure and free from corrosion. - Visual inspection reveals corrosion on connector terminals.
Diagnostic Steps
Professional Diagnosis Process
Follow these systematic steps to accurately diagnose the issue. Each step builds on the previous one to ensure accurate diagnosis.
- STEP 1 - Initial Visual Inspection: Begin with a visual inspection of the A/C system components, including the compressor, wiring harness, and fuses. Check for any visible signs of damage or corrosion at connections. Ensure that the A/C fuse is intact by using a test light or multimeter to confirm continuity.
- STEP 2 - Check Refrigerant Pressures: Use a set of A/C manifold gauges to measure the high and low side pressures while the A/C system is running. Ensure that the pressures fall within normal operating ranges. A low side pressure reading of 120 psi suggests further investigation into the refrigerant levels and potential blockages.
- STEP 3 - Test A/C Relay: Locate the A/C relay in the engine compartment fuse box. Remove it and test for continuity using a multimeter. If the relay fails the continuity test, replace it with a new relay. Ensure that the new relay is compatible with the Nissan Pickup model.
- STEP 4 - Voltage Testing at Compressor: With the A/C system activated, use a multimeter to measure the voltage at the compressor connector. It should read approximately 12V. If no voltage is present, trace the wiring back to the A/C control switch and check for any breaks or shorts.
