124 climate control issue

[McLoffs]

I have a '93 300E and have recently been having issues with the climate control. Before this, it's always worked perfectly (as far as I could tell, anyway).

A couple of days ago we got into the car after some shopping and the climate control would do nothing but blow cold air, no matter what settings were tried. We turned it off for about 15 minutes and when it was turned back on it was fine. Over the past couple of days it's hasn't done anything that bad, but there have been times where it feels like it's malfunctioning before quickly starting to work again.

Any ideas how I'd go about diagnosing this? A search of the forum find that there are a lot of vacuum problems with these systems and I'm thinking it might be something along those lines but I'm not sure.

Thanks,
Mike