Sampler motor is to the right and below the glove box, check this first. The pull the trim off the climate control pushbutton unit (two screws underneath on the earlier cars, not sure about later ones) and squirt some contact cleaner in the rheostat for the temp wheel.

Last, and this will be a pain if they are bad, check the vac servos for leaks. You need to remove the glove box (push rivets -- pull the center "plug" out and the rivet should lift out and two screws for the latch loop. Pull the top down to release the hook and pull out, disconnect the lamp wires). Attach a Mitivac each of the vac lines on the vertical switchover valve and see if they hold. If not, you have air direction problems, too, and the dash has to come out to replace them.

I expect either the aspirator or the temp wheel to be the problem. My TE, prior to the recent evaporator/vac servo replacements would do just what yours is -- get cold, then blow hot, then get cold, with the fan randomly running at full speed, then slowing way down. Works perfectly now.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!