Diagnosing AC Pressures Using Auto Refrigerant Gauges
Refrigerant is a gas that changes states and temperature by increasing or decreasing pressure. The refrigerant will probably not get cold enough, or at all, if the pressure in any system component is not at the necessary PSI. You can better diagnose AC pressures and common problems by using auto refrigerant gauges.
Every automobile has an onboard air conditioner as standard equipment. Still, some people will notice that their car's air conditioner isn't as cool as it was when they originally got it. There's likely a problem with the air-conditioning pipeline's pressure in this scenario. We can utilize the automotive air-conditioning pressure gauge at this point to see if the refrigeration system is broken.
Reading AC Pressures Using Auto Refrigerant Gauges
Multiple reading units, such as MPA, bar, KPA, and PSI, are included on the air-conditioning pressure gauge. Everyone should be aware of the unit of measurement conversion:
1 MPA = 10 Bar = 1000 KPA = 145 PSI
The atmosphere, engine speed, condenser cooling conditions, and other elements all influence the pressure value of automotive air conditioners. High-pressure gauges and low-pressure gauges are the two automotive air-conditioning pressure gauges. The red gauge indicates high pressure, whereas the blue gauge indicates low pressure.
There's no such thing as a constant standard. For example, if the outside temperature is 20 degrees Celsius:
- High-pressure value: 1.3-2.0 MPA (188-290 PSI)
- Low-pressure value: 0.12-0.25 MPA (17-36 PSI)
While operating the automotive air conditioner with engine speed maintained at 1500-2000 RPM, normal values are typically High: 1300-1600 KPA and Low: 150-250 KPA.
Common Diagnosis of Car AC Problems
To begin, measure the pressures at idle and note the HIGH and LOW side pressure measurements. These pressures will vary based on ambient temperature, but you should aim for:
- Low Side Pressure: 30-40 PSI
- High Side Pressure: 150-175 PSI
If one or both of these parameters are not met, use the scenarios below to investigate your issue further.
1. Not Enough Refrigerant or Failing Compressor
Symptoms: Both the low-pressure and high-pressure gauges are lower than average.
This is a fairly regular occurrence. In some cars with long service life and a slow refrigerant leakage, injecting refrigerant might temporarily remedy the problem.
The Test: Rev the engine to 2000 RPM with the instruments connected and observe the pressures. Do they get closer together (high side drops, low side rises), or further apart?
- Move Apart: The system is working but likely undercharged. Start by evacuating and recharging the system to the correct weight.
- Move Together: You likely have a faulty compressor.
Important Note: Before reassembling a system after compressor failure, it is necessary to replace the compressor, expansion valve, and receiver/drier, and flush the evaporator, condenser, and lines. In some modern vehicles (like Fords and Chevys), the condenser cannot be flushed effectively and must be replaced.
2. Failing Expansion Valve
Scenario A: High/High Readings
Both the low-pressure and high-pressure gauges have higher readings than average. The cooling effect is poor because the expansion valve is stuck open, flooding the system.
Scenario B: Vacuum/Low Readings
The low-pressure gauge shows a vacuum, while the high-pressure gauge reads lower than average. The evaporator expansion valve is stuck closed, starving the evaporator. In both cases, replace the expansion valve.
3. Moisture in the System (Freezing)
Symptoms: Abnormal fluctuations or dropping into a vacuum.
If you find yourself in this circumstance, there is likely water in the system. When moisture freezes in the expansion valve or orifice tube, it blocks flow and creates a vacuum in the low-pressure line. Once the ice melts, pressure returns to normal. To fix this, you must evacuate the refrigerant, pull a deep vacuum to boil off moisture, and recharge.
4. Failing Air Conditioner Compressor
Symptoms: The low-pressure gauge reads higher than usual, whereas the high-pressure gauge reads lower than usual.
If this occurs, the compressor is not creating enough pressure differential. It is failing internally and must be replaced.
5. Under Charged or Leaking System
Visually inspect the system for any leaks. Examine the hose ferrules and fitting connectors at the condenser, compressor, evaporator, or expansion device for oil residue. If there's no evident leak, recover the refrigerant, repair the service ports or valves, then evacuate and recharge the system. Adding UV dye can help discover leaks in the future.
Get the Right Tools
These are just a few examples of what could go wrong. Keep in mind that each vehicle is unique, and there is a variety of controlling and monitoring devices that can cause your air conditioning to malfunction.
HVAC specialists and individuals in Australia can purchase professional auto refrigerant gauges from HVAC Shop. We also have other HVAC products that may be useful for your air conditioning business!