you may also want to check the condition of the ACC monovalve diaphragm. My 83 300D cycled like that and it was mainly due to the monovalve. that being said... the cabin temperature sensor tube was disintegrated too but the main reason was the monovalve.

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1983 M-B 300D, 148K, daughter's ride
1983 M-B 300TD, 120K, my ride
1985 M-B 300SD, 102K, wife's ride
1969 HD FLH, 45K, restored/hobby
1996 Chev Suburban, family taxi/tow vehicle
1990 John Deere Model 240
1942 John Deere Model LA
1985 16' 4Winns ski boat