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Warning about testing the Cooling fans...
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Jack Lowry
Be Very Very Very Careful when trying to test a fan by wiring 12 volts directly
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from the battery. The fans draw a lot of current (thats why the fuses are 50 amps for each fan) If yor use a wire heavy enough to power a fan and get it wrong by connecting to ground lead of a fan, the wire will probaly weld itself at both ends, get really hot and if you are lucky the wire will brun through. If you are not lucky the wire will continue to pass a lot of current, causing the battery to generate a lot of hydrogen. One little spark possibly form the wire finally burning through, or you cutting the wire, and you'll have a problem that's rivaled only by fuel leaking over the distributor. I'd suggest that you follow the troubleshooting guide that I've put togather. Provide my guide will help you test the fans, medium speed relays, high speed relays, resistors and fuses. The only part that can't be easily verified (ask me I've been there) is the low speed relay, this relay has two sets of contacts one for each fan. There is two of everything else fans, fuses, medium speed relays, high speed relays, and resistors. -----Original Message-----
From: Michael G. McCarthy [mailto:mgmccarthy@...] Sent: Sunday, May 21, 2000 8:40 PM To: ev_update@...; ev_update@... Subject: Re: [ev_update] Cooling fans... You can test the fan motor by wiring 12 volts to it from the battery. Use a heavy wire, and you should be able to tell which terminal is plus and which is minus (although I don't think it matters; if you get it backwards the fan will just spin backwards). The big resistors contol fan speed. If they are crumbling I wouldn't trust they are passing electrons properly, although they might. Thermo-switches are BLUE, and make sure the connectors are cleaning and actually making connections before ruling them out. There are two on cooling hose coming off the front of the engine between number 1 and 2 cylinders. ---------- From: "John F. Gladu" <grungy@...> To: ev_update@... Subject: [ev_update] Cooling fans... Date: Sun, May 21, 2000, 8:25 PM Where were we? Driver's side fan runs (both speeds). Passenger side fan does not run. The fuses are good. My VW guru suggested checking the resistors behind the panel under the left headlight. I did - both are crumbling, but still passing electrons. I'm going to check on replacing this assembly. I may have to bite the bullet and buy a Bentley manual - I can only guess at the wiring without one. I still haven't figured out where the actual thermoswitch is that regulates fan operation. The louvers are opening properly on the back of the fan housing. How can I test just the fan motor? Can I just connect the two terminals on the fan to a battery? What do the big resistors do? bcnu - Grungy '93 Eudoravan MV ------------------------------------------------------------------------ Did you know you're using eGroups now? Start a free email group today at ------------------------------------------------------------------------ ------------------------------------------------------------------------ Avoid the lines and visit avis.com for quick and easy online reservations. Enjoy a compact car nationwide for only $29 a day! Click here for more details. ------------------------------------------------------------------------ |
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Michael G. McCarthy
The point was to test if the fan was defective, that's all. ?Take a heavy wire and connect the ground side with some sort of solid connection between the fan and the battery. ?Take another heavy wire, connect it solidly to the positive side of the battery. ?Then, take the remaining end and momentarily touch it to the remaining connection on the fan. ?If the fan fires up or remains dead, your diagnosis is complete. ?You don't have to run the fan for a long period of time and risk taxing the current carrying capacity of your temporary set up. ?A few seconds is all it takes to determine if the fan spins or not.
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50 amps at 12volts is 600watts. ?That's about the current draw of a large screen TV. ?That's a lot compared to most current draws in a car, but it's hardly "unsafe" if you use heavy wires. ?The point is just to test the fan, nothing more. Don't make it more complicated than it has to be. ?KISS. Mike ---------- From: Jack Lowry To: "'ev_update@...'" Subject: [ev_update] Warning about testing the Cooling fans... Date: Sun, May 21, 2000, 10:23 PM Be Very Very Very Careful when trying to test a fan by wiring 12 volts directly |
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In a message dated 05/21/2000 10:57:32 PM Eastern Daylight Time,
mgmccarthy@... writes: 50 amps at 12volts is 600watts. That's about the current draw of a largeMike - I believe you mean that is the POWER draw of a large screen TV. Regardless, 50 amps is nothing to play around with. I agree with Jack: Such testing deserves a lot of respect, and connecting a questionable motor, which may draw 50 amps when operating normally, to a battery which can deliver 100's of amps, and doing so without proper fusing, is not showing a lot of respect. A person performing such tests should have knowledge of the consequences that Jack is referring to. Pity the poor uninformed home mechanic who gets his wedding ring welded to the contacts of this high amperage source: he not only has lost a sentimental item, he may well lose the finger that once displayed that item! Bill Armstrong, EVC Speculator Endwell, NY '71 Econoline (home brew camper (54K Mi)) |
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Michael G. McCarthy
Correct, I should have said "power draw", not "current draw" -- my mistake. ?Amps are a measure of current, volts are a measure of what is roughly comparable to pressure, and watts are a measure of power. ?Amps x volts equals power.
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And also correct, be careful. And also correct, show respect for the hardware. Now, please, before you test your fans, please observe the following: ! -- Do remove your wedding ring. 2 -- Also be sure you aren't standing barefoot in a puddle of water. 3 -- Also make sure you use INSULATED wire (please! -- don't try this with a coat hanger). 4 -- Also, if the wire you choose is just a TINY bit too short, DO NOT ?-- I repeat DO NOT -- try to span the gap with your tongue! ?Just get a longer wire, or see your qualified service technician. 5 -- Don't forget to prop up the hood either (how many times have you seen it happen? ?-- someone lifts the hood, leans in to inspect the engine bay, forgets to prop the hood open, and then lets go -- OUCH!. ?Make sure the hood is secure before you let go!). 6 -- Remember that when you are looking at something with your own two eyes, objects are NOT "closer than they appear". Finally, the point is just to check if you've got a dead fan or not. ?This process involves safely getting some juice (current or power -- NOT orange or grapefruit) directly to the fan for a second or two. Mike ---------- From: WSArmstron@... To: ev_update@... Subject: [ev_update] Re: Warning about testing the Cooling fans... Date: Thu, May 25, 2000, 2:47 PM In a message dated 05/21/2000 10:57:32 PM Eastern Daylight Time, |
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