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Technical  Air Conditioning Sensor

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Technical  Air Conditioning Sensor

Shadeyman

Shadeyman

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Before I attempt a DIY refill of the air con, I decided to plug FiatECUScan in to check the presure.

0.00mb :eek:

But I also got "Air Conditioning Sensor Signal" fault.

So I used the presure gauge that came with the AC refill kit to double check the pressure manually. It was low but not Zero. So can anyone tell me where this sensor is and how to check it because I suspect the sensor is sending false info to the ECU.
 
linear press sw.JPG
On a 1.6 the linear pressure switch is at the front driver's side and it should be the same for most Stilos

linear press sw graph.JPG
It detects too low or too high pressure and won't let the compressor start up unless it's happy with it in the mid band. It doesn't sound as if there's anything wrong with it from what you've said so far. It's telling you that you have insufficient pressure and you have! You can override the switch if you are careful and know what you're doing with a variable resistance potentiometer but it's a safety device so you need to be careful what you're doing and why

It might be a bad time at the moment weather wise to try to refill the system as aircon will switch off below around 3C to prevent damage to the system through freezing up

Aircon isn't too difficult to understand but there are whole forums just on car air con so it's a mystical science lesson and very difficult to generalise and advise. If you know the pressure is low but you don't have a leak then I would put some mix in until the compressor starts up.

Most of them gradually lose pressure over a long time, very few are perfectly sealed
 
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I thought the Sensor / switch was on the drivers side UK
where the pipes feed in to the condensor. Would suspect
the sensor is ok you just have a leak probably on the pipe
bends near the switch.

John
 
I don't know what fault code you have but the air con sensor (linear pressure switch) warning should disappear when there is sufficient pressure in the system

Once the compressor starts up then let it run and settle down for a while so the gas gets evenly distributed throughout the system and then see where you are but with a temp of minus 3 out there at the moment the compressor may not even be allowed to start

linear press sw 2.JPG
You could check whether the LP switch is saying ok/not ok by return signal voltage as %age of 5v from the above chart. Certainly around 3v would be an "Ok for go on compressor " and, that's how you can induce it to start by simulating an ok voltage. Supply voltage on pin 2 will be around 5v, signal on pin 3 somewhere between 1-4v
 
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Also aircon is usually restricted switching on or below
a temperature of 3 degrees.
If all pressure has been lost suspect the alloy pipes
or schrieder valves. The pipes line fracture around the
pipe bends you can't tell unless the systems pressure
tested I've taken mine off and alloy welded mine
but my schrieder valves seap and loose pressure now.

Fault code will clear with FES or by disconecting
the battery, when the system holds pressure.
It will return if the system looses pressure and
the air con is then turned on with low pressure.

John
 
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Topped up the system a little, used the kit gauge to bring it up into normal operating pressure, marked on the gauge.(2 bar)

Soaked an old towel in warm water and wrapped it around the driver side mirror, External temp 16.5C. (y)

Started the car. Plugged in FiatECUScan and cleared the low pressure fault.

Fault reappeared 4 seconds later. Did this 5 times, same result.

Found the Air Conditioner Pressure Switch and unplugged it.

Checked for faults again, same problem.

So with the system at normal operating pressure I still got the same error code with or without the Low Pressure Switch connected. :(

Any suggestions?
 
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I'd remove the LPS connector and check for near 5v arriving at the LP switch on pin 2 and earth on pin 1

pot 3.JPG
Then, with a variable resistor, with one end connected to the 5v supply and the other to the signal return on pin 3 I'd adjust the resistance until it gave around 3v output. You've now simulated the sensor beiing happy with the pressure so it will allow compressor start up. A 10k ohms pot would be fine

Now with engine running and aircon switched on you should be able to turn on and off the compressor simply by turning the resistor up and down a little. Only do it just to test it and watch yourself though with those belt and puleys suddenly starting up, use around a metre length wires
 
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Before I start messin with multimeters and variable resistors I thought I'd wrap a hot towel around the drivers mirror of mt own car and tried the same thing to see if the clutch on the Air Con Pump would engage.

It didn't. :confused:

So could the air temp monitored by a different sensor, perhaps one on the heater intake and not the one in the drivers mirror?

Edit.
"A 10k ohms pot would be fine". Will this do?
http://www.maplin.co.uk/Module.aspx?ModuleNo=2205&OrderCode=FW02C
 
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Yes that 10k pot will do fine and the linear scale movement one you've selected is better for control than the logarithmic one

Have a look here at a guide i did for the eng temp sensor as that's the same idea
https://www.fiatforum.com/stilo-guides/104106-testing-radiator-fan-engine-temp-sensor-circuits.html

Then you can test the compressor, the clutch and have the air con system power up without having to mess about with warm towels and stuff. Do it just to test though and turn it off again

Some Stilo aircon systems measure the actual air con gas temp in the cabin for freezing, others go by the outside temp sensor

If the A/C powers up then I'd switch off and reattach the LPS connector and back probe the connector on pin 3 to see what output signal it's actually giving. Below 1v or above 4.2v and that will show it's not happy

So test for 5v there and earth and see what signal voltage it's putting out
 
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If I rig up the 10k pot, will the fact that the air temp is below 3C stop the air con firing up?
Yes it's a safety feature to prevent freezing up ut if it works on the outside temp sensor bulb then just having it in the sunshine will be enough to raise the temp enough

The 10k pot should solve the P0530 error I guess?
Well it will over ride it but not cure it.

If it does, is the Pressure Sensor is pooped?
Not necessarily, it needs 5v and earth at the sensor and the wiring between the sensor and the ecu could be suspect. Have to check it out
 
Deckchair5 said:
If I rig up the 10k pot, will the fact that the air temp is below 3C stop the air con firing up?
Yes it's a safety feature to prevent freezing up ut if it works on the outside temp sensor bulb then just having it in the sunshine will be enough to raise the temp enough

The 10k pot should solve the P0530 error I guess?
Well it will over ride it but not cure it.

If it does, is the Pressure Sensor is pooped?
Not necessarily, it needs 5v and earth at the sensor and the wiring between the sensor and the ecu could be suspect. Have to check it out
Click to expand...

So if there's 5v at the sensor and the 10k pot allows me to clear the P0530 error is the sensor pooped then?
How do I tell if the sensor is pooped?

Is it possible to run a supply directly to the + of the clutch on the compressor and fire it up that way?
 
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