Tag: ac compressor protection

Does a car AC compressor have a pressure relief valve?

Yes, automotive ac compressors have a pressure relief valve installed on their body.

What does an ac compressor relief valve in a car do?

The AC pressure relief valve is a safety device that protects the compressor from operating above its designed Maximum operating/working pressure.

The high -pressure relief valve is used to keep the system pressures from reaching a point that may cause compressor lock-up or other component damage because of excessive high pressures. When ac system pressures in a vehicle exceed a predetermined point, the pressure relief valve opens, venting refrigerant and reducing the ac system pressure .

The ac pressure relief valve in a car can fail in 3 different positions.

  1. Pressure relief valve stuck fully open.
  2. Pressure relief valve partially open.
  3. Pressure relief valve stuck closed.

What happens if the pressure relief valve fails ?

Signs of the ac compressor pressure relief valve failure

  • Pressure relief valve stuck fully open.

In this condition, the ac compressor will not be able to pressurize the ac system. The ac system will not hold the refrigerant charge for a long enough period to allow the ac compressor to raise the refrigerant pressure to normal ac operating pressures.

  • Pressure relief valve partially open.

In this situation ,the ac compressor relief valve remains partially seated. This condition is the most difficult to diagnose. The a/c compressor will operate and pressurize the system up to normal operating pressures and the overall performance of the car a/c system will be excellent but will slowly decrease over time ,because of the refrigerant leaking out from the not fully closed relief valve.

  • Pressure relief valve stuck closed.

This could result in a dangerous condition. The ac compressor pressure relief valve is a safety device intended to keep the refrigerant pressure circulating inside the ac system by the compressor below a dangerous point. The relief valve is the last safety resource used by the car manufacturer to vent the refrigerant out into the atmosphere before an ac component exceeds its safe working pressure and explodes. The ac compressor pressure relief valve is usually activated after all the other safety devices in the car were unable to stop the ac compressor operation.

Why is my air compressor pressure relief valve leaking ?

The air compressor pressure relief valve is a spring self-resetting device. The intended operation of the valve is to open when the refrigerant pressure inside the ac system exceeds a maximum pressure point ,usually between 350 PSI to 600 PSI. The normal operation of the relief valve is to open and vent refrigerant out into the atmosphere when the pressure exceeds the maximum level. The relief valve should reset automatically to the fully closed position when the refrigerant pressure is less than the internally calibrated spring force. In many cases once the valve opens it will not return perfectly to the fully closed position creating a refrigerant leaking point in the virtually sealed ac system.

What does the ac compressor pressure relief valve tell me about the overall condition of the ac system ?

  • Engine cooling system affecting a/c performance
  • Inoperative radiator fans
  • Underperforming fan clutches
  • Freon overcharge
  • A/C system contamination
  • A/C system contaminated with non-condensable gases

An ac compressor pressure relief valve fault should be the beginning of a deeper vehicle ac system diagnostic. A leaking pressure relief valve is a warning about an excessive high pressure in the ac system. Overlooking the warning sign of the valve could lead to expensive repairs in the automotive a/c system.

What happens when the ac compressor pressure relief valve in a vehicle is venting freon ?
  • A/C internal compressor failure
  • High side components leaking
  • A/C poor performance
  • A/C system contaminated with debris from internal compressor components.

Internal a/c compressor failure and system contamination often follows a leaking valve or indications of refrigerant venting from the valve. The cause of the valve opening condition should be found and repaired.

How to set the pressure relief valve on a car air compressor ?

The ac compressor pressure relief valve is calibrated by the manufacturer and there is no need to calibrate or repair. If the valve is leaking or faulty ,it should be replaced.

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Auto A/C compressor, compression Test.

To check the auto a/c compressor compression ratio, note on paper the low and high side gauge readings and add atmospheric pressure to both readings. Divide the high side reading (with the atmospheric pressure added) by the low side reading (with the atmospheric pressure added).The result should be between 6.5:1 and 7.5:1. A compression ratio of 8:1 or higher may cause compressor failure. Learn More…

The A/C compressor is considered the heart of the refrigeration system. Compression ratio is the technical expression for pressure difference. Compression ratios are used to compare pumping conditions for a compressor and is an efficient way to evaluate the health of an air conditioning compressor.

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Cars compressor repairs near me.

How to find an auto ac compressor problem, before is too late?

Check for high compression ratios.  To check a/c compressor compression ratio, note on paper the low and high side gauge readings and add atmospheric pressure to both readings. Divide the high side reading (with the atmospheric pressure added) by the low side reading (with the atmospheric pressure added).The result should be between 6.5:1 and 7.5:1. A compression ratio of 8:1 or higher may cause compressor failure.

Learn More.


AC compressor repair near me.

How to add oil to air conditioning compressor ?

how much oil does my car ac system need ?

how much oil does my car ac system need ?

The amount of auto air conditioning system oil and the correct type for the vehicle is vital to the life of the a/c compressor. Proper lubrication is a must for ac compressor long life. When the a/c compressor is operated ,oil gradually leaves the compressor, and the oil is circulated through the entire ac system together  with the refrigerant. After the air conditioning system is operated for the first time an oil balanced condition is reached in which a certain amount of oil is retained in the compressor and a certain amount is re-circulated through the ac system components with different amounts of oil depositing in them . If a component of the system is replaced after the system has been operated, we need to compensate for this by adding oil to the new replacement ac part.


Too much oil in the a/c system could result in extremely high head pressures which will cause poor air conditioning performance and premature wear and failure of the hvac compressor. If there is a surplus of oil in the system, too much oil circulates with the refrigerant ,causing the cooling capacity of the system to be reduced and the compressor head pressure to increase. Too little oil results in poor lubrication of the compressor and an increase in the heat of compression which shorten the life of the ac compressor.


When there has been excessive leakage of refrigerant, or it is necessary to  replace a component of the refrigeration system oil balancing is necessary to assure that the total oil charge in the system is the correct one after the leak has been repaired or the new ac part is installed in the car.


The recommended procedure step by step

  1. Measure the oil recovered from the system while recovering the refrigerant prior to part replacement
  2. Drain and measure the oil left in the old part
  3. Drain the new part(if factory oil-prefilled)
  4. Refill the new part with the same amount of oil removed from the old part and the amount of oil recovered from the system


The refrigerant oil required by the automotive ac system depends on a number of factors ,but it is primarily dictated by the type of refrigerant used in the system.R-12 car systems used a mineral oil. Mineral oil mixes well with R-12  without breaking down and losing its lubrication characteristics. Mineral oil however cannot be used  to lubricate ac systems with R-134a refrigerant.R-134 systems require a different synthetic oil,polyalkylene glycol (PAG).There are different blends of PAG and POE oil; always use the recommended by the vehicle manufacturer or the replacement part manufacturer.

The lubricant oil used in automotive air-conditioning systems is a non-foaming, sulfur free grade specially formulated for use in cars a/c systems. New refrigerants like R-1234yf might use PAG 46 and are backwards compatible for use with R-134a systems, but the R-134a old PAG 46 oils are not forward compatible with R-1234yf systems.


Add the recommend refrigerant  oil in the amount listed if you replace any of the following parts:
A/C condenser(including receive Dryer.25 mL (5/6 fl oz)
Evaporator40 mL (1 1/3 fl oz)
Line or hose10 mL (1/3 fl oz)
Receiver/dryer10 mL (1/3 fl oz)
Leakage repair25 mL (5/6 fl oz)
A/C compressorFor A/C compressor replacement, subtract the volume of oil drained from the removed A/C compressor from 82 mL (2 3/4 fl oz), and drain the calculated volume of oil from the new A/C compressor: 82 mL (2 3/4 fl oz) - Volume of removed A/C compressor = Volume to drain from new A/C compressor.
NOTE: Even if no oil is drained from the removed A/C compressor, do not drain more than 50 mL (1 2/3 fl oz) from the new A/C compressor.


automotive refrigerant control devices.

What is compressor protection ?

Some compressor clutch circuits contain a thermal limiter switch that senses compressor surface temperature. Some A/C compressor clutch circuits also contain a low-pressure cutoff switch. These are auto ac protection devices and their goal is the auto ac compressor protection.

A/C safety switches .

A/C systems have load-sensitive electrical switches; such as the low-pressure switch, high-pressure switch, pressure cycling, and power steering. Not all the switches, however, are used in all vehicles. The pressure switches are used to prevent compressor or component damage in the event of extremely high or low-system pressures.

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Thermal switches are used on both the low and high side of AC systems. A Thermal switch may be connected in series with the compressor clutch.

A/C compressor cycling control .

A thermostatic switch de-energizes the clutch and stops the compressor to keep the evaporator from freezing up. When the temperature of the evaporator approaches the freezing point (or the low setting of the switch), the thermostatic switch opens the circuit and disengages the compressor clutch. The compressor remains inoperative until the evaporator temperature rises to the preset temperature, at which time the switch closes and compressor operation resumes.

A/C Compressor temperature control.

A thermal limit switch may be mounted on or near the compressor and is used to stop compressor operation before the temperature of the compressor reaches a point of damage.


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What can I use to flush an automotive AC system?

Most vehicle manufacturers recommend closed loop flushing with air conditioning refrigerant as a flushing agent.  A benefit of this type of flushing is there is no danger of flush contamination,  since the flush agent being used is the correct refrigerant for the automotive A/C system.

Non-Approved Automotive AC flushes

Non-Approved flushes : Over the years many different liquids have been used as a non-approved flushes for A/C systems. The more common items are:

  • Alcohol
  • Brake cleaner
  • Carburetor cleaner
  • Mineral spirits
  • Penetrating oil
  • R-11, R-22, R-113
  • Gasoline

Automotive AC system contamination with liquid flush agents

The use of unapproved chemical flushes can result in damage to rubber components in sealing washers , compressor shaft seals , O-rings and hoses.

Automotive A/C compressor internal damage

Unapproved chemical flushes when mixed with the auto ac compressor oil , it will alter the viscosity of the oil as well. Any material left behind in the a/c system after flushing will dilute the lubricant and cause performance issues , increased compressor noise and premature compressor failure. If compressor failure is caused by non-approved flushing agent being left behind in the a/c system it can void the compressor warranty.

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How can I protect my car AC compressor

How can I protect my car AC compressor?

How can I protect my car AC compressor?

  • keeping your car ac system properly refrigerant charged and with the right type of oil and  balanced.
  • Maintaining the A/C condenser free from debris
  • Replacing an A/C condenser with missing or bent fins.
  • Keeping the Cooling system performing at 100 % efficiency
  • Checking the Cooling system fan clutch or electric fans operating at 100 % efficiency
  • A/C refrigerant system free from air or other contaminations.

Protect Auto A/C compressor against lack of lubrication.

With a large refrigerant undercharge, oil is pumped out from the compressor and becomes trapped in the evaporator or other ac components of the system and is unable to properly return to the hvac compressor. The amount of oil in the compressor can get down to dangerously low levels creating excessive heat and, in most cases, leading to failure of the unit. Some Air conditioning tests has shown that with an undercharged ac system, the oil amount in the compressor was reduced by over 57%.

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