ac compressor is turning on and off at idle any idea why?

[kninio]

HI to all ,

I lately recharged the gaz of the ac , and i notice that i have issue in the traffic when the car is idling the ac compressor play on and off and the rpm raise up and fall down unstable... , any idea why this compressor is kicking off from itself ?

any help will be appreciated

[Graham]

Either there is too much or too little gas.
The way it works is that there is 2 pressure switches on the condenser (infront of main Rad) One switch is High pressure the other is low pressure. When the compressor runs it has either got too much refrigerant and the head pressure goes too high which causes the HP switch to switch off the compressor till the pressure comes within range again, or when the compressor runs, it runs out of refrigerant, causing the head pressure to drop to the LP switch setting which again causes the compressor to cut out. The range is quite small aswell so you have to be accurate in the filling of the system. In normal operation the compressor should never switch off/cut out, unless the outside air temp is really high (40 dec.c plus) and your sat in traffic which has the effect of the head pressure going to high.

[johne]

Just to add a bit more information. There are actually 3 pressure switches in the system. The low pressure switch is inside the car on the back of the evaporator. The feed to the compressor clutch runs through it and it's function is to protect the compressor if you've run out of gas or the evaporator freezes up or you've got water in with the refrigerant. Given that you've just filled the system this is unlikely to be the problem.

The two pressure switches on the radiator in the engine compartment are both high pressure switches but set to different pressures. The lower high pressure switch brings in the radiator fan on stage 2 or 3 depending on fitment. The higher high pressure switch cuts the feed to the A/C compressor to protect the system from really high pipe bursting pressures.

When stationary, the system will heat up and the first pressure switch should come in pretty quickly to bring the radiator fan on. Is your radiator fan coming on? If it isn't the second stage switch will cut in and switch the compressor off causing the cycling you describe.

For reference, the low pressure switch will read short-circuit as long as there's gas in the system with the compressor running or not running.
The first stage high pressure switch is normally open circuit until it's pressure setting is reached and it closes.
The second stage high pressure switch is normally short-circuit until it's pressure setting is reached and it opens.

[kninio]

I have climatronic , any way to check the system with vagcom , i had no error codes last time any idea how to inspect it manualy?

thanks for the info mates i really appreciate that cos its bothering me the way its turning on and off..

[newsh]

Alternator belt slipping? If the voltage is dropping at idle the AC will drop out.