A/C diagnostics help

[jjrodger]

My air con ceases to function after about 20mins driving; the air supply just stops, although everything else keeps going. This does not happen in EC mode.

I have run the diagnostics. My evaporator temperature sensor reports 39 to 42 deg C at all times (I assume 42 deg C in the display means just that and does not mean 4.2 deg C), even when the car has been standing all night, and has not been switched on. I think the evap temp sensor must be faulty. Correct? I assume this would cause evaporator icing. How do I change the evap temp sensor? I know replacing the evaporator itself is a nightmare but I have heard the sensor can be changed more easily.

Also when I pull the error codes I get intermittent fault 419. I understand this is the electromagnetic clutch. What kind of fault could there be with the electromagnetic clutch? Could this be related to the evap temp sensor? The a/c works fine, nice and cold, for the first 20mins.

What is the spec pressure level for the refrigerant in the compressor? I am seeing less than 4bar quite regularly.

Thatnks in advance for nay help.

[LeaUK]

JJ

There is a TSB about this exact problem and it reads something like this:

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Occasional Air Conditioning Failure:

Condensation water enters at evaporator temperature sensor, the temperature of the condensation water is higher than the working temperature of the evaporator.

The HHT or DAS will not show a fault due to the evaporator sensor being damaged (ohmic values) by the condensation of water. The working temperature of the evaporator is between +2C and approx +12C

The A/C system will run for approx 10 minutes then the A/C compressor will switch off and will then run again for 10 minutes after the ignition is switch on.

Remedy:

Remove, install evaporator temp. sensor
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Looks very similar to me. Not sure about the clutch though. I guess the system looks to see if the clutch has engaged mechanically using a switch/sensor when it should and perhaps yours isn't going the full distance on occasion.

I'll have a look to see what I can find ;-)

Lea

[LeaUK]

JJ

Temp. sensor:

On a LHD '93 car the sensor is located beneath the instrument panel, behind the cover where your right knee is placed. However, I'm not sure how things are changed during manufacture from LHD to a RHD, but the drawing (for a LHD) shows it next to the cassette; on the left.

Fitting instructions are very straight forward, with the sensor having a simple two pin connector and so I guess the most difficult task is to find it!

[jjrodger]

Learoy, you must have the same Alldata subscription that I've just bought! I found the TSB you quote and I agree, I think this is my problem. If I get the time during the week I'm going to have a go myself. I don't suppose the design of the evaporator is any different for RHD, so I will start by grubbing around in my passenger side footwell. Do you know how to get in there?

Thanks for your help.

[LeaUK]

Just so happens I've had the passenger footwell out too, when I was searching for the ECU - LOL!!

Well, it wasn't actually me but I know it wasn't too difficult. The carpet was removed and the panel behind, this exposed the inners - took about 10-15 minutes for someone who hadn't seen how these come apart before - but he is in the trade.

AllDataDIY is a great tool and well worth the money but it will probably take you a few days to navigate around as it's huge. I'm still finding pages I didn't even know existed and I've had my subscription for over 3 months now.

Let us all know how you get on.

Cheers

[spomerle]

I have the same problem with my 99 SL500 as you described. Did replacing the evaporator temp sensor fix your problem?

[jjrodger]

Yes, fixed my problem. Cheap fix, too, the part was only GBP40. Other posters have suggested it is an easy DIY fix, although I got the dealer to do it.