AC low pressure fault stops compressor starting when recharge

[KiwiPete]

Hi, hope someone can help.
I have a 2007 C200 Diesel W204. The AC stopped working with an error code of 'Refrigerant pressure is too low'.

I bought a recharge kit but when I attach the gauge to the low side valve, it indicates the pressure is high in the warning zone over 100 PSI.
This is with the engine off or with the engine running. I think this might be normal when the compressor is not running.
The instructions in the recharge kit say run the AC for 3 mins before taking a reading. Problem is that the compressor won't start whilst there is an error code!
If I try to engage the AC by pushing the button the light flashes 3 times (also indicating the error).

I have cleared low pressure error code code several times (successfully according to the reader screen) but the code always returns the instant I start the engine.

Is there something I am missing - or does this indicate some other fault?
Is there anyway to force start the compressor - and will this reduce the low side pressure to enable a recharge?
Thanks in advance,

 

[MJJ]

The low and high side pressure will equalise 30 minutes after the compressor has run, so given your compressor is not running, I would consider the two sides equalised.

The resting pressure on a full, healthy system should be around 60 psi with the sort of temperatures we have currently. So, 100psi would either indicate there is too much gas in the system, or the recharge kit gauge is faulty. If the aircon worked before, then stopped and flagged low pressure, I would suggest the gauge is faulty.

On my S211, completely empty after fixing a leak, I cleared the low pressure fault code and started filling the refrigerant with the engine off. Then, once the first can was empty, started the engine and turned the A/C on. Worked perfectly for me.

If you want a second pressure opinion, I live not far from you (near Malmesbury) and have high and low side pressure gauges. I am no expert, but learned a lot - and bought the diagnosis kit - whilst fixing my car. I found this guys videos from the US very useful for understanding more about the aircon systems -

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If I were in your position, I would be clearing the fault code, emptying the can in (engine off), then running the compressor before disconnecting the can to get the last bit out.

Martin.

 

[alabbasi]

Did you check of your compressor is running? High pressure would be normal if the compressor is off. Get a proper set of gauges, that color coded crap is pretty useless.

 

[Doodle]

Surely the first thing to be checking here is that the low pressure fault is actually genuine and not just a failed pressure switch? The behaviour of the recharge kit would suggest it's not empty.

 

[KiwiPete]

Hi Guys, thanks for your replies - checked the pressure again this morning. It has dropped a bit to the yellow Alert from Warning. I understand this is normal if the compressor if not turning and this does suggest there is gas in the system.

Also checked the gauge on another car, when engine off got same high ready but when AC running got a green 'filled' reading so suspect gauge is prob good.

Re the pressure switch, how would I go about testing this. Do I just disconnect the terminal and see if the AC starts or do I need to short the terminals in the connector or something else. Not sure if material, the other AC error code is that the 'electric heater booster has a malfunction'. Thought could ignore this.

Thanks for your offer MJJ, might need to take you up on the offer.

 

[OneForTheRoad]

You need icarsoft to reset the ac after a regas. That's got to be done.

 

[zipdip]

Well I am not a great fan of these air con refill kits,I see your car is 13 years old,has the aircon ever been serviced or parts replaced,I use a specialist car air con company,called Into Cool they are about 20 miles from me,but they can save you a fortune because they understand the systems,unlike many garages that do refils and then change compressors and all sorts of things until they get it working,I see there is a mobile service based in Swindon called Auto Climate Control,of course it is up to you,but there are so many garages and people out their who mess air con systems up,I just like to go with companies that only tackle air con for a living.

 

[Petrol Pete]

ATS have a deal on at the moment, they are not AC experts by any stretch of the imagination but they are local and have better kit that most home mechanics .

In this heat it will be £50 well spent. Or for a professional more thorough job (bit more expensive) call Declan McCormack 07786 130525. He is local to you.

 

[Doodle]

Re the pressure switch, how would I go about testing this. Do I just disconnect the terminal and see if the AC starts or do I need to short the terminals in the connector or something else. Not sure if material, the other AC error code is that the 'electric heater booster has a malfunction'. Thought could ignore this.

Usually either check the output value on the switch with a meter or if the system expects it, short the connection and see if the compressor fires up