Air con faulty, but not faulty (apparently)

[JoolsPB]

Hi All,

I have a 2012 C3 Picasso 120 VTR+ which is currently blasting air out of the internal vents at what feels like somewhere around the temperature of molten lava while the air con is on and set to low. The first thought was possible low gas pressure so I bought a pressure gauge (low pressure only) and checked the pressure in the pipe, which came out as 150 psi, suggesting that it's both gassed, and b, that the compressor isn't having any effect as the low pressure side doesn't drop to around 30psi when it's turned on. However, when you switch on the aircon, you can hear the compressor engage and run, suggesting that the clutch is good.

I have a lexia 3, so plugged that in to check the sensors and switches and it registers the climate control buttons being pushed, and comes up with no faults when you run the troubleshooting option. Both internal sensors register 6500 degrees C which is apparently indicative of there being no cabin temperature sensors fitted. The other sensors tested at the same tine seem to pass, thought there's no visible test on the outside sensor in the mirror.

Basically, does anyone have any suggestions as it seems that all that should be happening is happening? I've fitted a new cabin filter and am hunting for any more sensors although I'd have thought that a faulty sensor would show up in the Lexia.

Thanks,

Jools

[Sloppysod]

Are your heater flaps working as they should?
In other words, if you turn your heater up do you get hot air or is it the same?

[JoolsPB]

Thanks for replying.

One of the odd things with it is that if the temperature is set to "Lo", it comes out insanely hot, but if you set it to somewhere nearer the air temperature, the temperature of the air from the blower seems to go down, or at least it feels closer to the ambient air temperature.

Now I've said that, it sounds ridiculous so I'm going to take it out for a spin and measure the air temperature from the blower at varying output settings.

[JoolsPB]

I think the temperature difference was my imagination. Anything below 28 C on the dials and it blows at 34 C. Over that, 50C.

[JoolsPB]

OK, I think we have a clue. About a week ago, the dog stopped recognising the car when it pulled up outside the house and it's just dawned on me that in the past, the thing that stood out the most is the roar of the fan behind the radiator which would cut out shortly after the ignition is turned off. So, last night, took it for a spin including sitting in traffic for some time and I don't remember hearing the fan so I suspect the ECU know the fan isn't turning and is disabling the air con.

So, does anyone know where the fuse for the fan is. I've checked the one in the glove box and the 40 Amper in the engine compartment but I then stumbled across mention of a "Maxi fuse" which is apparently a dealer job. Does anyone know where such a fuse may be hiding? Tonight I'm going to town with contact clreaner on all the fan related connections but, just in case, I'll check the "Maxi fuse" as well, if such a thing is fitted.

Cheers,

Jools

[ozvtr]

I bought a pressure gauge (low pressure only) and checked the pressure in the pipe, which came out as 150 psi, suggesting that it's both gassed, and b, that the compressor isn't having any effect as the low pressure side doesn't drop to around 30psi when it's turned on.

What pressure does it drop to? 150psi is only fair for the high side. If it's a hot day that's a bit low but you should be getting some sort of a result from the air con. When static, the pressure in the whole system is about 100psi. The low pressure should drop by as much as the high pressure rises. So my guess is the low side is about 50psi? Not great but I don't know what the ambient temperature is there. Again the aircon should be at least "cool".

However, when you switch on the aircon, you can hear the compressor engage and run, suggesting that the clutch is good.

In that case I would say your fan is running but it's easy to check...just look. If the engine ECU detects a fault in the fan controller it wont engage the compressor.

If the compressor is running feel the high and low pressure lines. The high pressure (small diameter pipe) will get hot and the low pressure (big diameter) will get cold. If the lines just get tepid then you have a problem in the gas side of things. If they are getting hot and cold respectively then your problem is in the air distribution box in the cabin. Possibly the mixer flap actuator is not working.
If you have a LEXIA you can cycle the mixer flap. LEXIA will give you a pass or fail on the actuator.

In 'Lo' even if the air con is not working, the air vent outlet temperature should be the same as the out side air. So my bet is a problem with the mixer flap or actuator. Unless the outside temperature is "as hot as lava".

[JoolsPB]

Thanks for the reply.

Last night I hooked the lexia 3 up and ran the tests on the air con control panel and the flaps. The software was reporting the flap positions changing but it's hard to know whether the software's measuring actual positions of just motor rotation. I'll be checking that tonight.

I'll be going over the rest of the system this weekend otherwise. I'm suspicious of the possible (lack of) fan noise so that's the starting point. I've found the location of the maxi fuses so that's the first check as well as separating all the connectors and giving them a squirt of contact cleaner. if that all checks out, it's off with the underside panels and arch liner and check the clutch and the power to it. If the power's there, it may be the actuator coil on the compressor.

Will let you know how it goes.

[ozvtr]

The software was reporting the flap positions changing but it's hard to know whether the software's measuring actual positions of just motor rotation.

The software reports the position of the output shaft of the servo. The flap "motor" is actually a servomotor. Usually if there is a problem with them, it's the gears inside the servo itself and it doesn't drive the output shaft. On some occasions the adapter between the servo and the flap would brake, meaning the servo would work correctly but the flap wouldn't move.

I'm suspicious of the possible (lack of) fan noise so that's the starting point.

The fan runs proportional to the pressure in the 'high side' of the aircon gas system. 'Lo' pressure, fan runs slow, high pressure fan runs fast. If the pressure is low (low gas volume, a leak) or it's not a very hot day, the fan might not even come on. However the fan also cools the radiator. When the engine is warmed up (aircon off) and at idle, the thermo fan should cut in and out every few minutes. But not as often as you might think.

check the clutch and the power to it.

You said you could hear the clutch engage. If you wind down the drivers window and raise the bonnet, you should definitely hear the clutch kick in when to turn on the air conditioning. The high side pressure is not going to go up to 150psi if the compressor is not running.

What is the pressure on the low side and are the vapor (low) and liquid (high) lines getting cold and hot respectively?