How to Repair Automotive A/C

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Step 1: Check the freon


To check the pressure of your freon, you will need a set of manifold gauges.

Here are some general recommendations for the pressures and temperatures of an air conditioning system dependent on the outside temperature. As a general rule, keep in mind that your real temperatures and pressures will fluctuate based on the air’s humidity level and the state of your system.

It is a good idea to keep a water hose close by and spray water on the air conditioner condenser when checking the freon level while the car is running at idle. In front of the radiator is where you’ll find the condenser. Read : Why is my ac not blowing air in my car

For vehicles currently running with freon R-134a only:

Outside Lowside Highside Center Vent Temp
90F 35-40 psi 190-225 psi 44-50 F
80F 30-40 psi 190-220 psi 43-48 F
70F 30-40 psi 190-220 psi 44-48 F
60F 28-38 psi 130-190 psi 44-46 F
120F 55-65 psi 320-350 psi 70-75 F
110F 50-60 psi 250-300 psi 68-74 F
100F 40-50 psi 200-250 psi 52-60 F


Run the fan on High, leave all windows open, and rev the engine to 1500 rpm when using R134a. The outside air temperature in degrees Fahrenheit should be between 2.2 and 2.5 times the high side pressure in PSI. For instance, if it’s 90 degrees Fahrenheit, the high side shouldn’t exceed 225 PSI.

Here is a helpful discussion for troubleshooting systems that use freon R-134a.

Problem: Compressor discharge pressure is low.


  1. System leak
  2. Faulty expansion valve
  3. The suction valve is shut
  4. Freon deficiency
  5. A receiver dryer with a plug
  6. Leaking compressor suction valve
  7. Defective compressor reed valves


  1. Fix system leak
  2. Replace valve
  3. Turn on valve
  4. Add freon
  5. Replace the dryer, and
  6. Replace the valve.
  7. Change the reed valves

Problem: Compressor Discharge Pressure at a High Level


  1. Air in the system
  2. a clogged condenser, and
  3. a blocked discharge valve
  4. Overcharged system
  5. Not enough condenser air
  6. A slack fan belt
  7. Condenser is too far from the radiator or not centered on the fan.


  1. Do system recharge
  2. Do condenser clean up
  3. Get the valve open
  4. Remove some of the refrigerant
  5. Install sizable fan
  6. Adjust the fan belt.
  7. Center and measure the distance.

Problem: Suction Pressure Is Low


  1. A lack of refrigerants
  2. A damaged compressor piston
  3. A leaky compressor head gasket
  4. Hose that is bent or flattened
  5. Leaking compressor suction valve
  6. Trash in the expansion valve or screen
  7. Moisture in the system


  1. Give additional refrigerant
  2. Replace the compressor
  3. Also replace the head gasket
  4. Change the hose.
  5. Alter the valve plate
  6. Replace the dryer
  7. Replace the dryer

Problem: Suction Pressure is High


  1. An inadequate expansion valve
  2. Overcharged system
  3. A jammed expansion valve
  4. Reed valves on compressors
  5. A compressor’s head gasket leak


  1. Get the valve tightened
  2. Remove some of the refrigerant
  3. Replace the expansion valve
  4. Change the reed valves.
  5. Change the head gasket

Problem: Compressor not functioning

  1. A faulty belt
  2. A damaged clutch wire or a lack of 12 volts
  3. Damaged piston in a compressor
  4. thermostat defect
  5. Defective clutch coil
  6. Low pressure switch has turned off clutch power due to low refrigerant.


  1. Change the belt
  2. Check for electricity or fix the wiring
  3. Change the compressor
  4. Change the thermostat
  5. Change the clutch coil
  6. give additional refrigerant

Problem: Evaporator Isn’t Cooling


  1. frozen coil; high switch setting
  2. slipping drive belt
  3. hot air leaks
  4. The receiver dryer is plugged
  5. Broken capillary tube
  6. Low refrigerant levels
  7. High head pressure
  8. Suction pressure is low
  9. Suction pressure is high
  10. A faulty expansion valve
  11. Freezing of the expansion valve


  1. Reverse the thermostat.
  2. Adjust the belt
  3. Look for vents or holes.
  4. Change the dryer
  5. Change the expansion valve
  6. Give additional refrigerant
  7. already explained above
  8. already explained above
  9. already explained above
  10. Change the expansion valve
  11. Remove and replace the dryer

Step 2: Flushing and Expantion Valve

You will need to remove the expansion valve, drier, and the compressor if you determine that the A/C system has to be cleansed to get rid of dirt and oils. PLEASE DO NOT FLUSH THROUGH THESE PARTS. Additionally, as oils often do not mix well, if you are retrofitting your system from R-12, you will need to drain off all the old mineral oil. Mixing oils or refrigerants will cause what mechanics refer to as “the black death.”


You can discover the evaporator to be exceedingly unclean once you’ve taken it out of the car. Remember to be extremely careful not to get water in the pipes that the freon runs through when cleaning your mines in the shower.

It wouldn’t be a terrible idea to repair the expansion valve and do your best to wrap it in some thermal insulation material if you had previously spent all that time pulling it out of the car. To keep it in place, I used tape and some packaging material. (On second thought, perhaps glue would have been a better choice.)

The process of flushing All you need to do is spray an AC cleansing substance into the freon pipes, which I won’t go into detail about. After waiting 20 minutes, blow shop air over it to clean it out. I had the good fortune to have access to my school’s shop compressor. You will probably have to wait for the tank to replenish if you use a potable one because it won’t be able to keep up with demand.

Step 3: Vacuuming

Every time the air conditioning system has been opened or pressure has dropped, it is crucial to replace the dryer. Due to the fact that the dryer absorbs any moisture that may have entered the system. Make careful to drain the oil from the old dryer before adding the equal quantity of new oil to the new dryer when installing a new one. Since the dryer loses its effectiveness after about two hours outside, do this shortly before cleaning.

It is now time to perform a vacuum. If you tend to use general purpose vacuum pump and it does not fit the manifold gauge hoses, then you might want to consider visiting your neighborhood a/c supply store where, more often than not, you may get the correct fitting at a reasonable price. If you already have an air compressor, you might want to consider an air-powered vacuum pump, which costs less than $50, as electric pumps can cost up to $200.

You must remove air and moisture from the system after the vacuum pump is attached. It is advised to carry out this action when the temperature is greater than 80 degrees. So, if at all possible, try to avoid doing it in the dead of winter. Allow a vacuum pump to operate for 20 minutes when it has achieved almost 30 in/Hg (inches of mercury), then turn it off.

Turn on the pump to remove the water if the vacuum begins to drop somewhat since this indicates that some water has evaporated. After that, let the vacuum sit for at least 45 minutes. If the pressure cannot be maintained, a leak somewhere in the system must exist. Before adding more fluid, make sure to fix it.