Hmmm. Few takers. My feet are getting cold.

I've ruled out the fan itself. The thing operates when cold with 12v on it, so it's something in the Climate Controls.

It will not run when cold. Not even the defrost. The colder it is, the longer it takes to start operating. It's not the engine temp that predicts operation. It seems to be the cabin temp, or some other factor.

Once something reaches a certain temperature, the climate control starts to kick in. It starts/stops/start/stops, then eventually stays on for the remainder of the trip. During the 'trying to start' period, there is a clicking noise each time it kicks in, and the light on the recirc button flashes with each click.

What in the system could be temperature dependent to this extent?
Is there a vacuum component to this? The vac pump seems to be working. The door locks work when cold, for example.

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1986 300E 5-Speed 240k mi.