OK I have been doing some reading so I can talk "A/C" to my NB's and it is a complicated language; not to mention the various dialects for certain model years. The reason I have done this is the wife's A/C has started shutting itself off, translated, melting the battery fuse block casing around the 30 amp fuse, and this occurs in stop and go, city traffic where the speed is 40 mph or less. I put a 15 amp fuse in it which blows without melting the plastic; a 20 amp fuse will still melt plastic. I used a rat tail file to reshape (fix) the fuse block.
One thing odd I did notice was that as long as the car is doing 40 mph or faster without any stops the A/C system works as advertised, even with a 15 amp fuse. So what A/C component is upping the power to which component?
Here is a list of the Sensors, Switches and Valves for the A/C system.
1) A/C Refrigerant High Pressure Switch F23 - Switches the coolant fan to next higher speed upon an increase of the refrigerant pressure to 16 bar.
2) A/C Refrigerant High Pressure Switch F118 - Switches off the A/C compressor when the refrigerant pressure reaches 32 bar.
3) A/C Refrigerant Low Pressure Switch F73 - Switches off the A/C compressor when refrigerant pressure drops to 2 bar.
4) A/C Pressure Switch F129 (Valve) - Does three things...
A) Switches the coolant fan to next higher speed upon refrigerant pressure to 16 bar.
B) Switches off A/C system if refrigerant pressure reaches 32 bar.
C) Switches off A/C system if refrigerant pressure drops to 2 bar.
5) A/C High Pressure Sensor G65 - Sends refrigerant data to the following Contol Modules and which control the cooling fans, A/C Clutch and/or A/C Compressor regulator Valve N280
A) Fan Control Module
B) Engine Control Module
c) Climatronic Control Module or A/C Control Head E87
6) A/C Pressure Temperature Sensor G395 - sends refrigerant data to the Climatronic Control Module J255, which in turn controls the coolant fans and the A/C Compressor Regulator Valve
7) A/C Refrigerant Shut Off Valve N43 - Switches refrigerant flow through the evaporator on or off.
8) A/C Compressor Regulator Valve N280 (internal component of the compressor) - Regulates the low pressure side of the refrigerant. If this valve is your problem you will need a new compressor.
Now depending on your the model year (dialect) of your NB, you will have one of the following A/C sensor system component setups...
1) F23, F73 and F118
2) F129 replaces F23, F73 and F118
3) G65 Replaces F129
4) G395 replaces G65 or F129
I have not read enough to determine which A/C system component setups comprise which model years. As soon as I determine this info I'll update this post.