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Old 08-01-2002, 07:09 PM
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Post hypothetical electrical question

My '40 Buick has what I assume to be about an 85 amp altenator charging system it. It has two, 1250cfm electric fans on the radiator, and a three speed electric blower on the the Air-Tique A/C unit. Whenever I turn the blower on, especially on "high" on the a/c unit,the gauge on Voltmeter drops to about 12V or sometimes slightly below if I am at a low engine rpm. The electric fans are on a relay, but the a/c blower is running thru the fuse block and is not on a relay. It has never caused any fuse blowing problems, but has got to be maxing out the system with both of these sets of fans running at one time pulling several amps. My question is: would it do any good to put a relay in the line to the A/C switch to help with the load that the fan motor pulls? Would this help the charging problem, or am I doomed to replace the altenator with a 125amp or better unit? Any help would be great, looking for the best way, not always the cheapest. Done been there and done that....PACO

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Old 08-01-2002, 07:57 PM
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Just my opinion but a relay is basically just an electrical on/off switch. If you were blowing fuses you could use a relay to limit the current through the circuit but the fans are still going to draw X amount of current. A relay will just redirect that current. At idle your alternator probably just can't keep up with the system demand. You're probably going to have to upgrade the alternator/voltage regulator. Do you have a solenoid to raise the idle when the A/C is on, picking up the rpm's may help. Even good systems sometime have trouble handling heavy loads at low rpm's. Sometimes you just need to find a way of getting that idle up a bit when loads are on. Newer cars use Idle Air Control valves to do this. I say this because even if you switch to a 125 amp alternator she's not producing that at idle. What was the original question? <img src="graemlins/spank.gif" border="0" alt="[spank]" />
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Old 08-01-2002, 08:05 PM
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If you have an 85 amp alternator, that should be sufficient to power the 2 cooling fans and the heater fan. No alternator will provide enough amperage to power all of that at idle. The addition of a relay for the heater fan will not make any difference in how much power it uses. Relays are used to keep switches from handling high current. I would have the alternator tested for rated output before I bought a bigger one.
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Old 08-02-2002, 06:11 PM
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I do not have a solenoid on the throttle to boost the idle when the a/c is switched on, but it would be a fairly easy thing to incorporate, and I'm sure some outfit sells a pretty billet aluminum one for just the right bucks. My alternator is a used one I had kept as a spare for several years until the older style alternators would not fit on the newer GM cars and trucks. A friend gave me a PowerMaster chrome plated alternator that would not work, so I swapped all the innards of the chrome one with my old stock one. That is why I assume it to be an 85 amp or so, because I don't have a clue what it really came off of, just that it was several years old. I kinda figured along the same lines yu guys did about the low idle/low output of the alternator, but it never hurts to pose the question. Some one out there has been there and done that, and can usually point me in the right direction. Thanks, guys, for all the info...PACO
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Old 08-03-2002, 08:00 AM
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I sorry, but I don't know how to speak hypathetical.


I know, smart ars answers are for general discussion. Had to do it! <img src="graemlins/spank.gif" border="0" alt="[spank]" />
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Old 08-03-2002, 07:07 PM
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just posting to say that the info above sounds good to me definetly check alt output and install a/c idle solenoid.. good luck oh and just want to say again i love that buick!!!!!!!!!!!!
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