Tech Tip: Knocking Noise Coming From Isuzu’s A/C System – UnderhoodService

Tech Tip: Knocking Noise Coming From Isuzu’s A/C System

A knocking noise coming from the A/C system of a 1992 Rodeo (UC) model (produced before 12/16/91, equipped with factory- or port-installed air conditioning), when the A/C is running may indicate that the A/C system is overcharged.

A knocking noise coming from the A/C system of a 1992 Rodeo (UC) model (produced before 12/16/91, equipped with factory- or port-installed air conditioning), when the A/C is running may indicate that the A/C system is overcharged. Follow the test below to determine a possible A/C overcharge condition.

Service Procedure:
1. Start the engine and set the A/C system as follows:
• A/C switch depressed (on);
• Blower fan lever to medium-high (#3) position;
• Mode lever to “vent” position; and
• Air intake lever to “recirc” position.
2. Open the vehicle doors.
3. Warm the engine to normal operating temperature and allow it to idle for five minutes.
4. Check the sight glass on the receiver/drier for a clear condition.
5. Disconnect the A/C compressor clutch lead wire.
6. Monitor the sightglass for a liquid level drop. The drop will appear as bubbles in the sightglass. Record the amount of time from compressor shutoff until the first sign of bubbles in the sightglass. This is the “drop time.”
7. Repeat the above test three more times, allowing the A/C system to run for about 30 seconds between each test.
8. If the average drop time of the four tests is above 50 seconds, or if drop times in all four tests are above 30 seconds, the A/C system is overcharged.If this is the case, the refrigerant should be recovered and the correct amount of refrigerant (2.2 lbs.) charged to the system.
9. Reconnect the A/C compressor clutch lead wire.

Courtesy of Mitchell 1.

For additional information, visit www.mitchell1.com.

You May Also Like

Jump Starting an EV

If an EV with a full battery won’t start, here’s how you can get it up and running.

Here’s a real-world scenario: A customer brings their EV into your shop for service, and it’s been there for quite a while because the parts are on backorder. After a few weeks, you get in the vehicle to move it out of your way, and the ignition won’t turn on. It’s acting like the battery is dead, so what do you do now?

Auxiliary Water Pump Diagnostics

A car or truck comes into your shop with a complaint of poor heater performance- the issue may be the auxiliary water pump.

Do You Know The Cause Of A No-Spark Condition?

A no-spark condition could be the result of communication errors or missing data from a dead module.

Belt-In-Oil Timing Systems

Oil contamination of the belt drive has been a death sentence, due to the rubber and fiber construction of the belt.

Building The Perfect Future By Mentoring

Share your stories of how you have helped others reach their goals.

Other Posts

Solving Intermittent Overheating

New cooling systems anticipate and influence changes in coolant temperature.

Spark Plug Fouling

Understanding why spark plugs get dirty.

PCV System DTC

PCV systems are far more complex now, but they are also much better at controlling crankcase pressure.

What Caused The Turbo To fail?

Up to 50% of turbocharger failures are due to oiling problems.