Think about it a second, ... "Fan speed changes with engine speed". Not to be sarcastic, but there's no throttle cable hooked to the fan motor. You can't be mad at me for questioning your competence because 99 percent of the people using this forum are do-it-yourselfers who will cause more damage and who will come up with a wildly incorrect diagnosis unless we set them straight. We have to start with the basics and most of the time that's the charging system that causes some of what you described. I would be lacking severely if I didn't pursue that line of reasoning long enough to verify to MY satisfaction it is not the cause of the problem. You would not believe how many people keep details secret and can't understand how to check for related observations, then we come to find out we could have solved the problem days earlier had we only known those details.
I still don't know what you're doing discharging a battery to do a test but I'm not going to insist you do something differently if you've been having success with your methods. The same goes for the 11.8 volts. That is indicative of a totally dead battery and that has no use in any type of test.
There's only two ways you can get 80 amps from an AC generator. Either it is an 80 amp unit that is good or it's a 240 amp unit with one defective diode. I've never seen a 240 amp generator on a car so it's pretty safe to say you have a good 80 amp one.
The next thing I have to ask, because I've seen people smarter than me do this, is where is the inductive probe connected? When I worked in a battery shop, the first thing we did was connect the load tester to the battery, then put the amp probe around one of the tester's cables to monitor how much current we were drawing. Next came the charging system test which required the amp probe to be moved to the generator's output wire. We got in the habit after that test "passed" to stop the engine, then draw a quick load again. If we got any current flow at all it was because we forgot to move the probe to the output wire and the current we were drawing was coming from the battery, not the generator. Probably once a month one of us caught ourselves making that mistake. In your case, since you obviously have a lot of time in it already, you would have noticed that, corrected it, and moved on, ... But I have to ask rather than overlook something stupid.
To get back to the fan motor problem, the next question is, was there anything actually wrong with the resistor? Since you said it acts differently now that you replaced it, either there was something wrong with the old one or you have the wrong new one. One of the old resistors could have corroded apart at its connection but more commonly the thermal cutout burns open. Many will still let the fan operate on the fastest speed when that happens. Tight bearings in the motor will slow it down leading to increased current flow. Over time that cause the thermal cutout to open. Now, with the new resistor assembly, if the motor is indeed tight, small changes in voltage can result in large changes in motor speed.
Some other clues to a tight motor are you may not feel any air movement on the lowest speed, and the motor will stop very quickly when you turn it off. The next place I'd go is monitoring the voltage right at the motor. Your symptoms do not suggest a corroded ground wire, but nevertheless, I would not use the body as a ground for the voltmeter. Use the motor's ground wire just to be safe. See what happens to the voltage when you change engine speed. If the motor speeds up more than the increase in voltage suggests it should, you have something limiting current flow.
I have to ask, so I know how to proceed, do you understand "back EMF" in a motor circuit and do you know the difference between voltage AT a point in the circuit vs. A voltage drop? Back EMF makes testing in motor circuits counter-intuitive to Ohm's Law and messes up a lot of really good technicians. If you know how to test for voltage drops, consider doing that in the fan circuit. In particular, measure across the switch contacts. Also look for blackened terminals on the switch assembly and on the resistor connector.
Check the battery voltage at idle too under varying loads. If it can't keep up with demand, do the voltage drop test between the generator's output terminal and the battery positive post. Whatever you find at the battery, you should find the same voltage feeding the heater switch when the motor is running. If it's substantially lower, look for a voltage drop across the ignition switch and any related fuses. A lot of manufacturers have been having trouble with ignition switch contacts that aren't heavy enough. A clue that I'm all too familiar with is a cassette player that sounds like it's changing direction when you roll two power windows down and they bottom out at the same time. That's an ignition switch problem. If you look for it, you'll also see the speed of the power windows is slower when the heater fan is on "high".
You have to use your judgement on whether the speed variation on the motor is really a problem or is normal. It IS common for a fan motor to slow down at idle speeds on many car models because generators are very inefficient at low speeds, but then you also should not have 14.2 volts. I'd expect to see the voltage drop a good half a volt at idle.
Getting back to "When I switch to recirculate I get no fan at all", if there's no computer involved, there has to be a problem with the switch assembly, in which case my entire story is irrelevant. If you can't see any blackened or overheated terminals in the connector, use voltage readings to verify a bad contact. If you have the wiring diagram, you can use a stretched-out cotter pin or piece of wire to jump the two wires together to verify the switch is bad.
Wednesday, June 20th, 2012 AT 1:40 AM