72 220d ac problems

[stands22]

I have been searching on here for a few hours now and just cant find my specific problem.
I recently replaced everything in the ac system just short of the evap and condenser.
It worked fine for a few weeks and the other day the interior fan quit and the compressor clutch wont disengage.
Where is my starting point for trouble shooting? I have a mess of money into this system and im just hoping someone will tell me its the switch but im at a loss of ideas at the moment.
The temp control that is supposed to engage the compressor shuts off the indicator light but the clutch dont shut off and the fan inside doesnt work at all.
i hope someone can give me some help

[alabbasi]

Have you put gauges on it to see if there is something going on with the pressures. The pressures can tell you a lot.

[stands22]

i charged the system to spec and everything worked fine.
the pressures arent going to tell me anything if the interior fan wont come on.
right now if i run the ac system the evap freezes up because there is no air flow
my question isnt about the refridgerant system its about the electrical system
i appreciate your help though

[alabbasi]

Right, fan aside, I'm not sure if these cars have a temp switch or a pressure switch which cycles the compressor. If it's pressure based, then a stuck expansion valve will give you low readings on the low side or high side (depending on which way it's stuck) which could keep the compressor from cycling. You can diagnose by reading the pressure.

Good luck with your electrical problem.

[79Mercy]

I think the problem your having is a very common issue on these cars. A problem with the fan switch with turns on the compressor and the blower.

W115's do not have any pressure switches. The climate control unit however should detect evap temp and regulate the compressor accordingly.

[Mike D]

The W115's have a separate compressor switch and a fan switch.

The compressor switch is a rotating knob. It engages the vacuum change over system. It re-directs the internal flaps to seal off incoming air, redirects the flow to the dash front vents, turns on the compressor and activates the fan switch (the microswitch mounted just above the acc. pedal).

The fan speeds are controlled by the same switch as for the heater.

It's not unusual to find a separate switch someone has wired in to manually work the compressor.

[stands22]

everything was working properly before the fan switch quit.
i still havent had time to investigate this problem further but i have 3 parts cars and a 45 year collection of odd ball parts and im curtain i will get it figured out after some of your ideas.
this car actually belongs to my grandpa and hes 82 now and cant to the actual work anymore but wants the car perfect and it looks the part.
i just wanted an idea of where to start and thanks again.
ill post the results

[Pooka]

If the compressor clutch will not disengage then it could be stuck. Find the wire that brings power to the clutch and unplug it. If the clutch does not release then it is frozen in place and needs to be replaced.

Since the clutch is pulled in by a large electromagnet your battery should run down since it powers the clutch magnet. You might also just disconnect your negative side of the battery and see if it releases. If not, it is stuck.

Is this a York type, a sort of big square thing, compressor?

[Mark DiSilvestro]

On these old Yorks, the compressor pulley & bearing is mounted to the clutch drive-plate. So if it stays engaged with the compressor-wire disconnected, the bearing has seized. The bearing used to be availible separately, but you'll need a press to separate and install a new one once you get the pulley/clutch assy off the compressor.

The AC-blower is separate from the heater blower. There is a vacuum-operated change-over switch above the accelertor pedal. Work the AC temp-control while observing if the change-over is happening. Also check the AC fuses - sometimes located in a separate small fusebox on the right firewall.
Any deeper into the AC-electrical may require wiring diagrams & 12V test-probe.

Happy Motoring, Mark