The OP asked how to wire up the relay which we posted. He was not asking how to re-design the A/C system or replace the switch. Some MBZ switches at the rec/drier work on temp, some work on pressure. Some need to discharge the freon, some doesn't. I do not know what he has. He just wants a simple hack or instructions. Why make life complicated for OP?

The hack is simple and does the job. Keep It Simple Stupid.

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Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.