Tag: AC poor performance

Different types of oil

how much oil does my car ac system need ?

how much oil does my car ac system need ?

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)
Evaporator 40 mL (1 1/3 fl oz)
Line or hose 10 mL (1/3 fl oz)
Receiver/dryer 10 mL (1/3 fl oz)
Leakage repair 25 mL (5/6 fl oz)
A/C compressor For 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.


The AC compressor should last for the entire life of the car,usually 8-10 years.

System maintenance and compressor efficiency

The compressors efficiency can be improved by maintaining the correct working conditions. This involves keeping the suction pressure as high as practical and the head pressure as low as practical within the design parameters.
A dirty evaporator will cause the suction pressure to drop. When the suction pressure goes below normal, the vapor that compressor is pumping become less dense and gets thin (sometimes called rarified vapor).The compressor performance declines. Low suction pressures also cause the high-pressure gases caught in the clearance volume of the compressor to expand more during the pistons downstroke.This gives the compressor a lower volumetric efficiency. These gases have to expand to a pressure just below the suction pressure before the suction valve will open. Because more of the downward stroke is used for reexpansion, less of the stroke can be used for suction. Suction ends when the piston reaches bottom dead center. Low evaporator pressures cause high compression ratios.
Dirty condensers also cause compression ratios to rise, but they do not rise as fast as with dirty evaporator.A dirty condenser makes the head pressure to rise. This causes the amount of refrigerant in the clearance volume (at the top of the compressor cylinder) to be greater than the design conditions allow and the compressor efficiency to drop.
If there is a dirty condenser (high head pressure) and a dirty evaporator (low suction pressure), the compressor will run longer to keep the refrigerated space at the design temperature. The overall efficiency drops.
Evaporator core and condenser core maintenance will increase the life of the air conditioning compressor,improve the A/C efficiency and cooling capacity.With regular A/C maintenance we are saving money in the long run and getting the most out of the air conditioning system.

What are the symptoms of a bad fan clutch?

Slipping fan clutch.

A slipping fan clutch would not affect ram airflow. This problem will reduce airflow at low speeds causing reduced air conditioning performance at low speeds.

Proper condenser airflow.

Reduced airflow across the condenser would elevate both the high and low side pressures. Airflow across the condenser is created by vehicle movement. A fan clutch allows the fan to freewheel when ram airflow is greater than the fan induced airflow. A slipping clutch would not change ram airflow.

A locked up fan clutch.

It is also common for a fan clutch to lock-up which will cause problems for the water pump, the belt drive, and the engines horsepower output. A locked up fan clutch will not reduce A/C cooling efficiency. Reduced airflow across the condenser generally affects the ability of the condenser to cool the refrigerant, resulting in higher temperatures and pressures in both sides of the A/C system.

Belt troubleshooting

Why do belts slip?

A car is equipped with an A/C compressor driven by a V-type belt. As the compressor cycles, the belt squeals briefly. A check with a belt tension gauge indicates the belt is correctly adjusted.

Belt slippage

A V belt that is not wide enough will run on the bottom of the pulley providing very little belt friction regardless of the correct tension. V belts get their friction by wedging themselves into the V groove.

What belt squeals when I start my car up?

An overcharged AC system condition can cause the high-side pressure to be so high as to resist the start-up of the compressor.

In the long run, the clutch or belt will usually fail.

air conditioning service near me

The air-conditioning system cools satisfactorily during the early morning or late evening, but does not cool during the hot part of the day.

The problem is that the A/C system seems to work fine in the early morning and evenings, but does not during the heat of the day. During a performance test, the low-side gauge reads normal and then drops dramatically.

  • Ice could be forming on the expansion valve
  • The receiver drier could be saturated with moisture

Moisture in the system can be released from the desiccant in the receiver-drier by an increase in temperature on the high side. When the ambient temperature is lower the desiccant may be able to hold the moisture out of the refrigerant. Internal freezing of the expansion valve could produce external icing on the valve.