Your problem is a fried resistor block

Editor’s note: Bob Sikorsky has retired from writing the Drive It Forever column. The new Drive It Forever columnist is Mike Allen, and this is his first. We hope you enjoy!

Dear Mike: The fan for the heater and a/c in my Dakota pickup works, but only on “high.” Any other setting, and there’s no air moving. This is true for both heating and air conditioning.

My mechanic can’t find the problem. He says that the fan motor is fine.

— A.G., Lutz, Fla.

A: Your mechanic is right about one thing: There’s nothing wrong with the fan motor. But he’s looking in the wrong place. The problem is a fried resistor block.

This is probably the most common failure mode of HVAC fans since heaters became standard equipment. This package of resistors simply goes in series with the motor to provide a range of lower speeds. When it fails, only the “High” switch position still works.

If you want to trying fixing it yourself, the part will cost about 10 bucks. In your Dakota it installs under the dash, near the glove box, and it’s held in a hole in the HVAC plenum with two small bolts. There’s a small tab on the connector between the harness and the resistor block that has to be depressed to pull them apart.

What’s a plenum? That’s the big plastic box surrounding the a/c evaporator, heater core and fan.

Why is this component placed inside the plenum, instead of someplace more accessible? It’s because this resistor gets hot, and whenever the fan is running there’s a breeze inside the plenum to cool it. It sort of defines the concept of air cooling, eh?

If you get to poking around underneath the dash with a voltmeter, don’t confuse yourself — this resistor is tied into the ground side of the fan motor. If you’re metering the positive side of the fan, you’ll always see 12 volts on the meter at any switch position, even if the fan is off. If you check continuity in the old block, you should see some resistance between all the pins and the common pin. An open circuit means a bad part.

On your Dakota, the common pin happens to be pin No. 2. Other vehicles may use different pin numbering, so check the schematic diagram.

Dodge obviously discovered a problem. The replacement resistor block now available at the dealership uses a wire-wound resistor on a ceramic insulator instead of resistance material silk-screened onto a plate. Upgraded parts such as this one are common after a year or two.

Dear Mike: I recently put about a gallon of water into my gas tank by accident.

As a fix, my stepfather put in about three gallons of premium gas and two bottles of fuel conditioner. He then replaced the spark plugs and cranked the engine over until he could smell gas.

Since putting in the new plugs, he’s used starting fluid to try to get the engine started, but no luck.

Is there any way to fix this, now that water is in the fuel lines?

— R.O., via e-mail.

A: By accident, you say? Gee, I would have guessed that you didn’t do it deliberately.

At any rate, premium gas won’t help at all. The plugs probably didn’t need to be replaced. And two 8-ounce cans of fuel conditioner aren’t nearly enough to soak up the water.

The pickup in the tank is probably immersed in the pure water/conditioner mix. Water is cosolvent with alcohol, the main component of these additives, but it’s not cosolvent with gasoline. Alcohol is cosolvent with both and, if you add enough alcohol, the water will mix with the gas.

However, if your tank is one-fourth water, you’d need to add way too much alcohol to accomplish anything that way. The maximum permissible alcohol content for conditioners is 3 percent to 10 percent, depending on the type of alcohol used, so your tank isn’t big enough to hold enough alcohol to get the job done.

If you have a fuel filter that’s accessible, go buy a new one. Get several gallons of denatured alcohol, at least 90-percent concentration. Break open a fuel line somewhere and run a hose to a collection vessel. Pour a couple of gallons of alcohol into the tank, and put a jumper on the fuel pump to get it to run.

Run the tank dry, pour out the goop you’ve collected — setting it aside for later disposal in an environmentally responsible way — and repeat. Replace the fuel filter and fill the tank with fuel. Now the car should start in a minute or so.

If your car has an in-tank fuel filter, it’s not that easy. You’ll need to remove the tank from the vehicle, drain it, dry it and then reinstall it with a new filter. Don’t forget to flush the fuel lines while it’s out.

And do all this today, before your fuel injectors corrode.

Dear Mike: It says in my owner’s manual to use only Honda ATF-Z1 fluid in the transmission of my Odyssey.

In an emergency, it says, I can use Dextron III, but then the Dextron must be flushed out as soon as possible and replaced with the Honda product.

I thought transmission fluid was universal.

— J.S., Spotsylvania, Va.

A: Used to be there were GM and Ford transmission fluids, and one or the other would work in anything. There were even some ATFs on the market that claimed that they would work under both specifications. No more.

Will your Dextron-adulterated Honda coast to a halt next week with its transmission a smoking ruin? Probably not. But will Honda deny a warranty claim if it can prove that you violated its recommendations? You bet.

Car manufacturers specify fluids based on criteria that include viscosity, friction characteristics, heat resistance and about 100 other things. If you replace the fluid around which they’ve engineered the tranny with something different, you may well feel a difference in shift quality and experience slightly reduced transmission life expectancy.

So I’d look for a transmission fluid that lists the Honda specification on the side of the bottle. And no, you won’t necessarily have to buy it at a Honda dealer.