Since both my '84 300D & '85 300TD have trouble maintaining heat as
chosen via the thumbwheel on the left of the PBU and I've been
through (including resoldering) the troubleshooting guide numerous
times for both units and not found a definitive problem. To explain
about the problem of not maintaining heat, what actually happens for
example when a temperature is chosen via the thumbwheel on the PBU
say just below the MAX (note: click stop setting), the heat will
gradually disappear within a couple minutes and I have to keep
switching to MAX, etc. Since I've inspected the neoprene seals of
the mono valve inserts in both cars using a 10X loop and haven't
been able to locate any very small holes, I recently purchased new
mono valve inserts and installed a new one in the 300D and drove it
this evening and had no heat no matter what . . . go figure. Like I
believe many others on this list, I wish these cars had the old
mechanical heating/cooling control system and not the dreaded
electronic fancilessness.
G. M. Brown
Brevard, NC
That is a bummer. I hope someone here can help you. Monovalve or
PBU are most of the problems, other than the pods and vacuum solenoid
switches. Seems like you have covered those.
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