ASE Certified Master Technician | CDL-A | PA Safety & Emissions Inspector
Justin Brojakowski is a seasoned automotive technician with over 24 years of hands-on experience diagnosing and repairing vehicles of all types. His career began in Chevrolet dealerships, where he spent nearly two decades mastering vehicle systems, leading teams, and tackling complex repairs. From engine diagnostics to emissions systems, Justin developed a reputation for precision and persistence, earning certifications in Pennsylvania safety inspections, emissions repairs, and A/C systems.... Read more
Customer Complaint
The customer brought the vehicle in, concerned that the air conditioning wasn’t cooling. We verified the concern and found the vent temperature reading 80⁰ with the AC on, set to vent position, and the fan on high.
Initial Inspection
We began by visually inspecting the AC clutch for operation and found the clutch would not engage even when the A/C was set on MAX at the lowest temperature setting and blower fan on high.
System Pressure Check
To determine whether the system was low on refrigerant, we checked the AC system’s static charge using the AC service machine and manifold gauge set. Always check both low and high side to get a good understanding of the charge of the A/C system. The static pressure was around 90 psi on both the high and low sides, with ambient air temperature at 82⁰—indicating the system was fully charged.
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Diagnostic Scan and Electrical Signal Check
Next, we grabbed our OBD-II scan tool and performed a code scan. No related codes were found in the A/C control unit. We then monitored the data parameter in the PCM for the AC request signal. We observed that the parameter changed from “yes” to “no” when pressing the AC button, confirming that the PCM received the request from the HVAC control unit.
Fuse and Relay Testing
Moving forward, we checked fuse F3 (AC clutch, 10 amp) in the underhood fuse block for power with the AC switched on. It tested okay at 12 volts. To further confirm circuit integrity, we inspected the AC clutch relay (K1) operation in the same fuse block.
With the AC switch on, we removed and reinstalled the relay while feeling for a click. The relay clicked on installation, indicating good power and ground to the relay’s coil side.
Clutch Connector and Power Verification
We then gained access to the AC compressor and inspected the clutch connection. It was plugged in and securely in place. After unplugging the connector at the AC compressor clutch, we examined the terminals for bent pins, corrosion, or damage—no issues were found.
To test the power and ground at the compressor clutch, we back-probed the connector and installed a test lamp. With the AC switch turned on, the test lamp lit up, confirming good power and ground at the clutch.
Turning the AC switch off extinguished the lamp, indicating the circuit from the HVAC control head to the PCM and then to the compressor was functioning correctly, with no short or open.
Final Electrical Test – Clutch Coil
For final verification, we used a DVOM across the terminals of the AC compressor clutch and checked for continuity across the clutch coil. A DVOM across test uses a Digital Volt-Ohm Meter (DVOM) to measure resistance (ohms) across the terminals. The DVOM showed an OL (out of limit) reading, indicating an open circuit inside the compressor clutch.
Diagnosis
At this point, the diagnosis was confirmed as a faulty A/C clutch. The continity test verified that the AC compressor clutch was inoperative due to an internal open circuit.
Repair Performed
We proceeded with replacing the AC compressor and clutch assembly, recharged the system to the proper level, and performed a final test. After the repair, the vent temperature dropped to 42⁰—confirming the AC system was now operating properly.
Verify Customer Concern
Confirmed AC not cooling properly.
Vent temperature measured at 80⁰F with AC set to vent…
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