Air Con: clutch not engaging

[KBB]

If you have climate control then the system is fitted with a pressure sensor and not a pressure switch. If this is the case then it is likely that the by passing has set an AC Excess High Pressure fault code (this will not trigger the MIL).

On these systems the Climate control module has no control over compressor clutch operation. The clutch operation is controlled by the Engine ECU based on a request for AC from the Climate module, the Engine ECU reads actual A/C system pressure via the pressure sensor (to check for too high/too low or within range pressure).

If the pressure is within range the Engine ECU will ground the control circuit of relay 2/10 fed via fuse A-30 and power the compressor clutch. It will also control relays 2/28 and 2/11 to control the 2 speeds of the condenser fan.

If I was looking at this I would be using a code reader that supports the climate system live data to see what pressure the sensor is seeing measured against my A/C manifold gauges looking at actual pressure. If you go to the connector at the compressor and jump a 12v supply to the violet wire and the compressor runs you will have at least eliminated the clutch from the diagnostic process and then focus on the control side of the system.

[elkopi]

thanks KBB,

firstly i do not know what do you mean by saying that the high pressure fault will not trigger MIL (what's MIL?)

secondly I did see the clutch engaging so I'm assuming it's fine. Also the mechanic did the proper refilling, so I'm also assuming the pressure is fine.

what i am actually bypassing is the connector (IMAG0739.jpg) at the top of the receiver/dryer (IMAG0738.jpg) which again I am assuming is a pressure switch.

how can i tell the difference between pressure switch and pressure sensor?

just to be clear:

1. when turning ac nothing happens.

2. then i disconnect the connector from the pressure switch/sensor. there are three prongs there (as in the image). when i connect two outside ones the idle goes up.

3. also when i start disconnecting the connector i get the fan working. first on speed 2 for a second and then it switches to speed 1 for another second or two. also with the fan going on i get the clutch engaging for a second.

it's just as if there was something wrong with the connector wiring. why would the fan and the clutch engage only for a second? and only when i play with the connector?

[960kg]

A MIL is a name for the fault light on the dash which lights when you have a fault with a system and A/C does not necessarily light this bulb they have there own system of Led sensors around the cabin and they will flash for 20 seconds if you have an A/C fault.

You have a Pressure Sensor as it is incorporated where the refrigerant is stored in the reservoir , the sensor as you know is on top where you plug the connector, it can be unscrewed and change BUT you have just had the system charged and it will have to be done again to change the sensor IF faulty.

A Pressure Switch is usually in the line of the pipes on it`s own.

I cannot help with anymore as you would need to read the error codes so it`s complicated.

When you visit an A/C specialist it`s alway`s best to say i have a fault and they will fix it and you should only get charged for one re-fill of gas.
But if you tell them what to do it can become expensive

....this concerns any garage with any problem.

Good Luck

[KBB]

A pressure switch can have either 2 or 3 connector pins as will a pressure sensor. The difference is a pressure switch is usually fitted to manual A/C and is in series with the A/C compressor clutch circuit.

With Climate control the actual pressure is monitored by a sensor. To confirm this if you leave it connected and with a DVM back probe each wire at the connector making sure one of your meter leads are connected to battery neg. If it is a sensor one wire will read 5v (this is the sensor reference voltage), one will read about 0.1-0.3v this would be sensor ground the third will have a varying signal voltage and any where between 0.5-4.5v system pressure dependent. As system pressure increases so will signal voltage.

When by passing if you have jumped the 5v reference voltage to the signal wire you are sending an artificial high pressure sensor signal and the Engine ECU will not engage the compressor clutch control circuit but may switch on the condenser fans as high pressure refrigerant is hot and needs to be cooled.

To be honest to get any where quick with climate control you need a scan tool that supports that climate control system with live data and bi-directional control. Live data is critical as the are many reasons why the ECU may not allow the compressor to run such as evaporator sensor reading too cold, out side ambient temp sensor reading too cold, too low or high system pressure. We use bi-directional control to override the ECU and force the compressor to run proving circuit control integrity, leaving us to investigate all the input signals via live data to diagnose the fault.

You can try the pot luck approach and change sensors and parts but I would not recommend it, very expensive and time consuming. I do not at the moment have access to VIDA but the may be some tech info explaining signal voltage reading against pressure to see if the sensor is reporting correctly.

[Dog_Book]

On my car the switch has 4. Find my thread if you want more detail.

[elkopi]

thanks guys,

I guess I will just try to find a garage that would diagnose the problem for me fairly cheap. If not I'll just leave it as I live in Scotland, so don't really need it.

The reason why I wanted to fix it is because I'm going on a road trip to Italy with my family and as you know it may get quite warm over there in summer.

Anyway, thanks you all