Mechanics

MY AC BLOWER MOTOR QUIT WORKING. REPLACED RESISTOR. NOW WORKS POORLY AND FAN SPEED IS REFLECTIVE OF ENGINE RPMS. IDEAS??

2004 Suzuki Aerio • 100,000 miles

Unit blows good cold air, just no pressure. I can't find the fan intake but with the glove box removed I can hear the speed change with RPMs.
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Acerockshard
June 19, 2012.



Before you go any further, the changing speed with engine speed might be a clue to have the charging system tested. Start with the battery voltage with the engine idling. You can measure that yourself with an inexpensive digital voltmeter. Next, have the generator professionally load-tested on the vehicle. Typically it should be able to produce somewhere in the area of 90 amps. If all you can get is one third of that, there is a defective diode inside the generator. The charging voltage may be okay at higher engine speeds but it will drop off a lot at idle.

Caradiodoc
Jun 19, 2012.
Sorry left that out. My amp clamp shows 80 amps after load testing the battery to 11.8 volts. Battery voltage 14.2 at idle.

Tiny
Acerockshard
Jun 19, 2012.
At 3000 rpm's fan runs 1/3 speed as normal high. When I switch to recirculate I get no fan at all.

Tiny
Acerockshard
Jun 19, 2012.
That sounds more like a switch problem.

As for the load test, it was loaded too much if the system voltage dropped to 11.8 volts. It has to be maintained at no lower than 13.75 volts and to be valid the engine speed must be at least 2,000 rpm. 80 amps is fine but only if it can be developed at 13.75 volts.

Caradiodoc
Jun 19, 2012.
I used the load tester to discharge the battery to sub 12 volts with the engine off. Then started the car to test charge and voltage rates. I am a John Deere master mechanic. I definitely know how to test a charging system. Why would the fan care if I recirculate. Why would the switch care about RPMs.

Tiny
Acerockshard
Jun 19, 2012.
I must say I laughed at the inexpensive multi meter suggestions. My Fluke amp clamp was not cheap. LOL

Tiny
Acerockshard
Jun 19, 2012.
I'm a master mechanic too, and I taught Automotive Electrical for 9 years at a community college. That doesn't prove I always know what I'm doing. The reason I specify a "cheap" meter is because I got yelled at once by someone who said they came to this web site because they were broke, couldn't afford a mechanic, and how in the heck did I expect them to buy a hundred dollar meter to use once. The Harbor Freight Tools meters that go on sale for $2.99 work fine.

I've been in tv / vcr repair for over 35 years and my most expensive digital meter cost 40 bucks on sale. Got twelve of 'em so I can find at least one when I need it! Don't have enough time left in my life to waste on auto-ranging meters that have to bounce around deciding which range it wants. I'm smart enough to know which range to select.

I'm not sure what you're referring to about discharging the battery unless you do that to give a place for current to go during the load test. That isn't part of any normal charging system test. In fact, no charging system test is accurate unless the battery is fully charged. Professional load testers use a carbon pile variable resistor to provide the current path up to well over 400 amps. A battery can't sustain a charge rate of much more than 20 amps without overheating. Regardless of your methods, any charging system test is not valid if the voltage is below 13.75 volts. You could compare that to a hydraulic pump. It must be good if it can deliver 10 gallons per minute, but what good is that if it can't build more than 20 pounds of pressure? Your generator might be able to deliver 80 amps but that is worthless if it can't get higher than battery voltage to charge the battery. If you're using a manually-adjusted load tester, you have to watch that system voltage never drops below 13.75 volts. If you can't get it higher than 11.8 volts, you're running off the battery, not the generator. Maybe tractors are different but if they're running a 12 volt lead-acid battery, the charging system will have the same requirements as on a car.

As for the switch assembly, the older mechanically ones that were perfectly reliable had a combination of vacuum and electrical switches. Each push button opened a set of vacuum ports to run the mode doors, and an electrical switch to turn on the fan motor. The electrical part could fail in any push button without affecting the others. Some used a series of plastic slides behind the switches that opened various ports and turned on the switches. On some, using the recirculate mode bypassed one fan resistor in the assembly to increase speed when you were running already-cooled air through again. In normal mode the condenser had a bigger heat load with the humid, hotter air coming in and they slowed the fan down to give it time to condense that humidity.

When we started going to computer controls we ran into all kinds of unusual problems. You can look as far back as the early '80s Cadillacs and Corvettes to see all the problems computers caused. It isn't always obvious either if the car uses an HVAC computer. Look at the miserable '96 Caravan with a pair of simple turn-knobs. There's a whole computer module behind them. You haven't experienced frustration until you tried to recalibrate one of those after disconnecting the battery. The same two knobs are used on the older Dodge trucks but instead of a computer they use a simple cable and electrical switches. Those never cause a problem.

Caradiodoc
Jun 19, 2012.
I already said, battery voltage at idle is 14.3.
80 amps. I have a knob and no computer. FYI, a 2012 Deere has the same charging system as my car. I do not have a charging problem.

Tiny
Acerockshard
Jun 20, 2012.
So in summary, you know nothing specific to my model and know little if anymore than I do?

Tiny
Acerockshard
Jun 20, 2012.
Put me back in the question pool please.

Tiny
Acerockshard
Jun 20, 2012.
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