Testing the Fan Clutch

dave lowry

New member
Jul 7, 1998
615
0
0
On our recent trip to Ukiah and back for the GMCWS rally (which was
terrific, by the way), we noticed the same "woo woo" sound as was noted in
an earlier post. I don't recall if a source of the noise was determined in
that thread, but I believe what I heard was the intermittent engaging of
our fan clutch. My hired "hands" and I tried to test it today, but couldn't
get conclusive results. It is a Hayden 2747 which was installed last August
and only has less than 7,000 miles on it. I'm not sure it ever worked
because we never did notice any noise upon cold start and didn't notice it
kick in even clearing the three 10,000+ ft. passes from Ouray to Durango or
on the desert highways heading west from Albuquerque. We have only had an
overheating experience once, and that was at well over 11,000 feet heading
east toward Denver, but I would still like to be certain it will work when
that time comes that we definitely need it.

We couldn't get conclusive results because we couldn't complete the test as
outlined in the manual. Let me describe what we did so that somebody who
has experience can hopefully tell me what to do next. I realize that the
quick solution would be to just have a new 2797 put in, and that may well
be what I end up doing, but that type of answer has been a little too
common lately causing us to stockpile of good used parts and deplete of our
RVing budget.

1st, I had him turn the fan by hand. It had a slight drag on it at the very
beginning, but after 3 or 4 turns the drag became less. The manual says
this is not good, but that a replacement decision shouldn't be based solely
on this test, so we proceeded.

Next, we covered about 75% of the radiator with cardboard, installed a
thermometer between the radiator and the fan and started it up to get
things warm enough for the fan to kick in. 20 minutes later, engine temp.
was holding at only 180 with no fan engaged. To get things a bit warmer, we
covered the remaining 25% of the radiator and turned on the dash A/C. After
another 10 minutes it was still 180 according to the oem gauge and the
Digi-panel, and still no fan engagement. Now I can hear y'all saying "I
should be so lucky", and the test we did might satisfy you, but I'm not
satisfied. The fan clutch is there for a reason and I want to know it will
come on when needed.

So, is there anything else I can do to find out conclusively if the clutch
is working? And if it has to be replaced, are there anything I need to pass
on to the installer to help insure the next one works?

Dave (advisor/navigator) & Dege (ALL else), '76 Royale, Santa Barbara, CA
 
>
> .... Let me describe what we did
>
> To get things a bit warmer, we covered the remaining 25% of the radiator and
> turned on the dash A/C. ....... Now I can hear y'all saying "I should be so
> lucky",
>

Dave,
Stop while your are ahead.
You are right, I wish I had been so lucky last summer when I performed the
clutch test exactly the way you and the shop manual describe it. In my case
when I covered the radiator with the cardboard (which also blocks air flow
through the condenser), a fitting on the high pressure hose on the air
conditioner compressor blew letting all my freon out of the system and about
$500 escape my wallet to get the thing repaired. The A/C shop repair man told
me that its very risky to perform this clutch test because of the high
pressures that develop in the A/C system. His advice and mine too is to
replace the clutch if you don't hear it roar when it is supposed to. Its a lot
cheaper than risking the freon blow out like I had. None the less I'm glad for
you good luck.
Phil Stewart
'76 Transmode, TN