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  • Writer's pictureMarco Bonifaccino

Car Air-Conditioning: check and service.

Updated: Apr 26, 2022

Here you will find useful basic information and handy tips relating to air-conditioning systems in vehicles.

Important safety information

The following technical information and practical tips have been compiled by AC diagnosis, source HELLA, in order to provide professional support to vehicle workshops in their day-to-day work. The information provided on this blog is intended for use by suitably qualified personnel only.


The air-conditioning system used to be something reserved for luxury cars. Today it is standard equipment in all vehicle classes. But how does it achieve cooling and which components are actually involved? Here you will find not only find answers to these questions, but also tips on the maintenance, troubleshooting, and repair of air-conditioning systems.

In this article, we're going to talk about:

  1. Function: Air-Conditioning cirquit

  2. Useful information: Air-Conditioning service, recharge and check

  3. Troubleshooting: checking the Air-Conditioning system

  4. Workshop tips: car Air-Conditioning repair - removal and installation instructions



Refrigerant and the cooling circuit are required to control the climate inside the vehicle. A blend of cold and hot air makes it possible to create the desired climate conditions ─ irrespective of the conditions outside. This makes the air-conditioning system a key factor in improving safety and driving comfort.

The individual components of the refrigerant circuit are connected by hoses and/or aluminium pipes and thus form a closed system. Refrigerant and refrigerant oil circulate in the system, driven by the compressor.

How the air-conditioning system with expansion valve works

The circuit has two sides:

  • The section between the compressor and the expansion valve is the high-pressure side (yellow/red).

  • The section between the expansion valve and the compressor is the low-pressure side (blue).

The gaseous refrigerant is compressed by the compressor (thereby significantly increasing its temperature) and pressed under high pressure through the condenser. This removes heat from refrigerant - it condenses and changes its state from gas to liquid.

The filter dryer, the next unit, removes contaminants and air from the liquid refrigerant as well as humidity. This ensures system effectiveness and protects the components from damage caused by contaminants.



Alternating check and service

The air-conditioning system is a system requiring maintenance. It should therefore be inspected at regular intervals in order to prevent damage.

The air-conditioning check and air-conditioning service are comparable to a small and large inspection:

QUICK TIPS. Expert recommends: Perform the air-conditioning check every 12 months and the air-conditioning service every 2 years.



Testing the cooling capacity

In addition to test tools and special tools, every garage requires the relevant specialist knowledge, which can be acquired through training. This applies in particular to air-conditioning systems. Due to the different systems, these instructions can be used as guidelines only.

Correct evaluation of the pressure manometer display is particularly important.



1.Spare part inspection

Before removing or installing a spare part, check whether the connections, mountings, and other installation-relevant characteristics are identical.

2.Use new O-rings

When replacing components, always use new O-rings suitable for the refrigerant.

3.Keep the system closed

The compressor oil has a pronounced hygroscopic effect, which is why the system should remain closed as much as possible and the oil only added shortly before the refrigerant circuit is closed.

4.Grease the O-rings and seals

Prior to the installation, O-rings and seals are to be greased with refrigerant oil or special lubricants in order to facilitate installation. No other greases or silicone spray may be used as this results in immediate contamination of the new refrigerant.

5.Renew the dryer

Every time the refrigerant circuit is opened, the dryer must be replaced due to its pronounced hygroscopic effect. If the dryer or accumulator is not regularly replaced, the filter cushion may become separated and distribute silicate

particles throughout the entire system, which can cause severe damage.

6.Seal off connections

The connections of the system should never remain open for an extended period and instead be immediately closed, or sealed off, with caps or plugs. Not doing so will introduce the humidity of the air into the system.

7.Use two wrenches

In order to avoid damage to connection pipes and/or components, always use two wrenches when loosening and fastening the connections.

8.Watch out for damage due to vehicle edges

When routing hoses and cables, take steps to avoid causing damage by contacting vehicle edges and other moving components.

9.Ensure correct oil quantity

When replacing a component of the air-conditioning system, the correct oil quantity in the system is to be ensured. Oil must be refilled or drained as needed.

10.Before filling, check for leak-tightness and evacuate

Before refilling the system, the system must be checked to ensure that it is leak-tight. The system must then be sufficiently evacuated (approx. 30 minutes) to ensure that all humidity is removed.

11.Before filling, check for leak-tightness and observe the pressure values

After filling using the quantity of refrigerant specified by the vehicle manufacturer, check the system to ensure that it operates as intended and is leak-tight (electronic leak indicator). At the same time, the high-pressure and low-pressure values must be monitored using pressure manometers and compared against the prescribed values. Compare the outlet temperature at the centre nozzle with the values defined by the manufacturer.

12.Affixing the service label

After the service connections are fitted with protective caps, affix a service label sticker on the front crossrail to verify that the maintenance work has been carried out.

1 Comment

Feb 18, 2022

Whenever you want to repair or service your AC unit, always contact AC repair diamond bar experts because they have the knowledge to deal with all types of HVAC systems properly.

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