The radiator should only go into high speed when low speed no longer does
the job. For AC it is common for the fan to switch from low to high speed
during extended idling or accelerating after an idling period. If the
refrigerant high pressure switch is putting the fan in high speed too often
it is a sign of an overcharged system or something else wrong such as a bad
expansion valve, clogged receiver dryer, bad-dirty condenser or contaminated
to much oil in the refrigerant. 

Dennis

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
David M
Sent: Friday, June 24, 2011 7:33 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Vibration when radiator fan on high speed

Just paid $1200 to have my van worked on (a/c fixed, fuel tank resealed,�
gearshift linkage, oil change, emissions). Mechanic said fan should be on
high-speed whenever a/c is on, is this true? 
Now I notice a really bad vibration (can feel it thru pedals) when a/c fan
is on high. 
Could this vibration have to do with fuel tank being dropped and
re-installed?
I dont know if fan was ever on high before but I never noticed this
vibration back when the a/c worked before (10 years ago).
Also van now has no pick-up whatsoever, I press the gas pedal and it takes
forever for me to take off.
Regarding a/c all mechanic did was fill it with freon R12 (3 1/2 pounds cost
$262.50).
It was $400 in labor to do the gas tank with me supplying the kit of parts.
The oil change cost me $106.50 because the drain plug stripped and labor to
install a helicoil was $80.
I have to take van back on Tuesday for them to check if any of the valuable
freon has leaked out.
Its so frustrating that whenever I take my van in to be worked on., it
always comes back with the original problem fixed but with a new set of
problems appearing!

-David (1987 Wolfsburg)