Thanks for the help.. can you indicate where is the RCV in the Golf Mk4 please? Is it found in the compressor itself? Or is it the expansion valve?As he said, it does NOT cycle off and on. It's always on, but the compressor uses a RCV - refrigerant control valve, to regulate the compressor in producing the correct freon flow;. I am pretty sure the RCV uses the fan setting to modulate this.
Thanks for the reply.. my evaporator is getting below 0 degrees and freezing up.. What can possibly do this? All equipment is OE and I am suspecting the expansion valve to fail! Any advice is welcomed.. Thanks a lotUnder normal operation these are considered 'non-cycling' compressors. They are variable displacement. The only time the clutch will disengage is if the system is too low on charge or in rare cases the engine controller requests full power and it disengages but on the diesels that hardly ever happens.
This being said.. I am thinking more and more about the evaporator expansion valve failing then! Am I right?The A4 Golf has a purely mechanical control valve inside the compressor, under the head. The A5 and newer cars use an electronic RCV, and those compressors have no clutch.
I am a complete noob at this.. any idea of the value that mist be charged in the unit?If the evap is freezing the most-likely causes are the expansion valve OR it is low on charge. If you KNOW you have the correct charge in the unit (because you put it in there) then its probably the TXV.
Thanks again for the useful information.. one last thing.. the evaporator is supposed to cool down at which temperarure? The expansion valve regulates the evaporator at 6-7 degrees? Right?Yep and the only way to properly charge automotive systems is by weight. They will run ok down to about half charge, but start to get squirrelly.
One thing to remember is that the refrigerant is the coolant for the compressor, and when you compress a gas it gets VERY HOT. Anything that impedes proper circulation of the refrigerant risks the compressor overheating, the oil will coke inside and once that occurs the damage is progressive and usually terminal. This is also why the fans are critical on these cars; unlike a gas car that will overheat almost immediately without the fans working properly these engines rarely overheat with one or even none of them running. However the A/C compressor will overheat and there is no sensor for that and thus no warning when it does before it is damaged or destroyed.
If you ever completely discharge an auto A/C system (e.g. due to a leak -- its illegal to intentionally vent refrigerant to the atmosphere) you must change the dryer and then immediately pull a hard vacuum before charging it. The chemical in it is one-way, it has little capacity, and any amount of water vapor in the system will react with the refrigerant under heat and pressure to produce an acid which then proceeds to eat everything made out of aluminum (that's most of it, including the evaporator) from the inside out.
True, it's not a totally on system and I wasn't clear, but i meant when the system is turned on by the fan switch there isn't supposed to be a cycling off and on by the compressor.The system absolutely will cycle the compressor, weather for low evap temp or not I don't know. It does kick the compressor off for low and high system pressure to protect the compressor.