Based on the archives here, I already know that my power transistor is dead. Only the highest speed has worked since last October (probably longer than that, I had no a/c last summer and didn't notice the dead 1-3 until I had the condenser replaced). Now the highest fan speed doesn't work and I'd rather troubleshoot this new problem and have my dad or step dad do the fix.I can find my way around my car with direction-can someone would be so kind as to tell me what things to check to locate the problem before throwing parts at it? I have access to a voltmeter.

I couldn't quite find direction in the archives--keep in mind, I need simple directions (I know more about cars than a regular schmo, but not that much).

Also, is an a/c recharge a simple DIY job? I seem to remember something about an"explosion" if you do it wrong, so I'll take it into Midas or somewhere if it means keepingour limbs intact.

 

If you have a '95, there's no power transistor. There's a fuse, the switch, a resistor pack, and the motor. Start by putting a voltmeter on the motor terminals and turn the key on and switch on high. If you have 12 volts but the motor doesn't turn, then the motor is bad. Working on high but not the other speeds is usually the resistor.

Your A/C should not need recharging unless there's a leak, which should be found and repaired first. But obviously you'll never get any cool air without the interior blower working, so the rest of the system may be fine. Don't try recharging the system with the little Wal-Mart hose. If you're willing to spend about $300 on some special tools and learn how to do it, you can do it yourself.

 

You don't really need $300 worth of the tools. You just need a manifold gauge set($50-$100) for automobiles. Hook up the gauges and run the A/C for a bit. Check the pressure on the high side and the low side. Should be ~100-200PSI for the high side and ~30PSI for the low side. The only time when it gets expensive is if you get a vacuum pump. They are very helpful for fiding leaks. Put the A/C under vacuum for an hour or so to get everything out. Turn the vacuum pump off. Come back later and check the pressure. The system should still be under vacuum. If its doesn't hold a vacuum, then you have a leak. As my autoshop teacher always told me, the best tool for diagnosing A/C is your hand. Check the high side and low side A/C refrigerant lines while the A/C is running. The high side should be hot (be careful, you can burn yourself) and the low side should be cold. If it isn't, then you have a problem. Your blower might not be working, but checking the A/C lines should tell you if your A/C is working. Make sure the A/C light turns on and then check the lines. Also, you can check to see if the blower motor itself is working by checking the resistance of the coil. It should have some resistance. You can also wire the motor to a battery and see if it turns on.

 

I had my dad play around with the fan tonight and the fuses and relay are ok (but who's to say they won't poop out on me tomorrow). He gave the motor a nice thwack with the butt end of a screwdriver and the fan came right on. It worked for the rest of the night, but it does have a bit of a gravelly sound to it (which I've heard before). Question is, what could the gravelly sound be? Worn bushings? Debris? It's about to die? If it's any of this, is it user-replaceable or would I be better off buying a new motor? Installation looked very simple, so that's not a concern. Anyone have a estimate on the cost of a new motor before I go calling around once it dies again?

Also, my dad wanted to know how the fan speeds are regulated if I don't have a power transistor.

 

It seems it's about to die because the brushes are worn down so they don't make contact any more. The motor is not intended to come apart and I doubt you'll ever find a way to buy parts for the inside. So replace the motor as a unit.

The resistor system simply passes the motor current thru a coil of resistance wire to reduce the voltage reaching the motor on speeds lower than high. More and more resistance is switched in for the lower speeds. The resistor gets hot so it is mounted in the air duct to keep it cool. Until fairly recently, every car used that system because it is cheap.

 

Some systems use a 3 resistors wired in series. Resistor1-Resistor2-Resistor3-Motor. When you choose speed 1, you wire power through resistor1 and this gives you a really low speed since current needs to pass through all 3 resistors. Speed 2 is a bit faster since current only has to pass through 2 resistors. Speed three is even faster since current needs to pass through only 1 resistor. Speed 4 is the fastest because it does not have to pass through any resistors.