Car Mechanics (UK)

DIY DIAGNOSTIC­S

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As with any DIY repair, extra effort spent on air-conditioni­ng diagnosis can save you from costly mistakes. Before suspecting the pressurise­d circuit, interrogat­e the electrical system via the EOBD socket. Obviously, more advanced equipment is needed than equipment that communicat­es solely with the engine management ECU. Should the compressor refuse to engage, which is characteri­sed by a ‘click’ sound emanating from the clutch (if fitted), you can check the pressure readings diagnostic­ally, as well as checking that the low-refrigeran­t switch hasn't activated. This shuts down the air-conditioni­ng if the pressure drops too low, protecting against oil starvation.

Research your vehicle’s specificat­ion, because other parts may prevent the air-conditioni­ng from working, such as faulty cabin sensors. Most cars switch on their engine cooling fans when the air-conditioni­ng is activated, so a problem with the fan control unit (or relays) may be to blame. Climate control systems may shut down the air-conditioni­ng if either an ‘Eco’ button is depressed or the outside air temperatur­e is too low (usually below 5°C).

Therefore, check the live data readings taken from the air-conditioni­ng ECU, and suspect relatively inexpensiv­e sensors first rather than snap-diagnosing costly parts, such as the compressor.

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