Automotive Air Conditioning Information Forum (Archives)

Provided by

We've updated our forums!
Click here to visit the new forum

Archive Home

Search Auto AC Forum Archives

How do you test the fan clutch?

BG1 on Fri July 23, 2010 12:31 PM User is offline

Year: 1990
Make: Chevy
Model: 1/2 ton pick-up
Engine Size: 5.7
Refrigerant Type: r134a

How do you test the fan clutch? I had the AC manifold gauges on the AC system and tried water across the condenser and it really dropped the pressures. I thought the fan clutch was bad because it was real tight to turn by hand and replaced with a new one but it was as tight when taken out of the box, so I do not know if this is a good one or if its bad.

SeppW on Fri July 23, 2010 1:40 PM User is offline

The following is procedure I've read in several places and likewise, I've read to replace them at each water pump change. I recently changed the original one on my '95 Suburban. It wasn't leaking and passed the spin test, but it didn't seem to engage when it was supposed to and it had a lot of lateral slop when rocking the blades back and forth. So I just replaced it.

I read in one article to roll up newspaper and stick into the blades at idle. I would not recommend such a move. Seems idiotic at best.

Of course, the part is fairly inexpensive and easy to get to. Just make sure the replacement is the correct one.

Not sure about the temps in the procedure, if they're vehicle specific or general to viscous clutch fans.


If the fan assembly free-wheels without drag (the fan blades will revolve more than five turns when spun by hand), replace the fan drive. This spin test must be performed when the engine cool. For the following test, the cooling system must be in good condition. It also will ensure against excessively high coolant temperature.

WARNING: Be Sure That There Is Adequate Fan Blade Clearance Before Drilling.

1. Drill a 3.18 mm (1/8 - inch) diameter hole in the top center of the fan shroud.
2. Obtain a dial thermometer with an 8 inch stem (or equivalent). It should have a range of 18° to 105°C (0° to 220°F). Insert thermometer through the hole in the shroud. Be sure that there is adequate clearance from the fan blades.
3. Connect a tachometer and an engine ignition timing light (timing light is to be used as a strobe light).
4. Block the air flow through the radiator. Secure a sheet of plastic in front of the radiator (or air conditioner condenser). Use tape at the top to secure the plastic and be sure that the air flow is blocked.
5. Be sure that the air conditioner (if equipped) is turned off. WARNING: Use Extreme Caution When The Engine Is Operating. Do Not Stand In A Direct Line With The Fan. Do Not Put Your Hands Near The Pulleys, Belts Or Fan. Do Not Wear Loose Clothing.
6. Start the engine and operate at 2400 rpm. Within ten minutes the air temperature (indicated on the dial thermometer) should be up to 88° C (190° F). Fan drive engagement should have started to occur at between 74° to 82° C (165° to 180° F). Engagement is distinguishable by a definite increase in fan flow noise (roaring). The timing light also will indicate an increase in the speed of the fan.
7. When the air temperature reaches 88° C (190° F), remove the plastic sheet. Fan drive disengagement should have started to occur at between 57° to 79° C (135° to 175° F). A definite decrease of fan flow noise (roaring) should be noticed. If not, replace the defective viscous fan drive unit.

Then again, I'll defer to the practitioners here.

bohica2xo on Fri July 23, 2010 2:13 PM User is offline

Testing fan clutches


"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

Back to Automotive Air Conditioning Forum

We've updated our forums!
Click here to visit the new forum

Archive Home

Copyright © 2016 Arizona Mobile Air Inc.