At 12:47 PM 5/19/2013, george jannini wrote:
>   Should I put mr. resistor on my list of "spare crap I always need to
>carry with?    :-)

The fan in an A/C 2.1l Vanagon has three speeds:

a) Low speed from the rad thermoswitch (paralleled by the A/C relay)
through both parts of the resistor to the fan.

b) Middle speed from the A/C high-pressure switch through the A/C fan
relay and one part of the resistor.

c) High speed from the rad thermoswitch through the rad fan relay
straight to the fan.

As long as the thermoswitch AND (either both sides of the fan
resistor OR the relay) are working you've got a radiator fan.  If the
thermoswitch dies you can fake it by turning on the A/C with temp set
to maximum.

Normal A/C operation sequence:

a) Radiator fan runs at low speed whenever system is on, A/C ups it
to second speed if the high-side pressure rises too far.

b) Compressor clutch will engage if ambient temp >/= 5C/41F AND rad
thermoswitch first speed not active (indicating that the first-speed
fan can't keep up with the load and the system is heading toward
high-speed operation).

There's a good deal of redundancy.  I don't think you'd need to carry
a spare normally.  But the backstop spare would be the radiator fan
relay for the high speed, if you were going to carry one thing.

Note: this doesn't take the A/C system itself into
consideration.  There's no high-pressure shutoff on the compressor,
only the mid-speed fan.  Perhaps the answer is inspect the resistor
and replace if it's deteriorating.

Yours,
David