Car Help: When AC Belt Drives Power Steering

My wife’s car is acting up. It appears to be the clutch of the AC compressor. I’m out of town, but apparently the AC belt started burning. An auto friend of ours looked at it and it sounds like the root cause is the AC compressor clutch. But, I am hearing this second hand. Anyway, our mechanic friend says the AC belt on this car also drives the power steering. My question is:

How does the same belt drive the power steering with the AC off? Does the clutch act as an idler gear allowing the belt to slip over it? And, if this is correct AND the clutch is bad…can the car be driven without worry of the belt breaking? And, if the belt breaks, is the car still ok to drive - like a car without power steering? Or, does the car become impossible to control once this belt breaks?

Yes, if the same belt drives both the AC and power steering, the AC pulley acts as an idler. When the AC compresser needs to be driven the clutch engages and provides rotation to the compressor.

If the belt is slipping over a non rotating pulley the belt will either burn or break. Sometimes both.

Once the belt breaks it will be difficult, but not impossible to steer the car. I’d advise against it myself. The belt might also drive the alternator.

If you can post the year, make and model we might be able to determine what belt drives which accessories.

Thanks for the advice! BTW, it’s a 2002 Mazda Protégé LX.

Well, here’s a link to a diagram of the 2002 Protégé belts, but I find it confusing because it seems to indicate that sometimes the same belt drives the AC, power steering, and alternator. Other times it seems to not be the case.

I’m hoping someone else comes along soon.

Thanks for the advice. (We’ll have to figure out what to do. My friend, the mechanic, works long hours. I hate to bother him, and he often does not have the time. My regular mechanic is 30 minutes away because I’m not thrilled with any local mechanics.)

the A/C compressor clutch disengages when the A/C is off, and the compressor pulley free-wheels.

also, on pretty much every car since the '90s, there’s ONE belt which drives all the engine-mounted accessories.

Have you tried just unplugging the compressor?

If the fault is that the clutch isn’t disengaging properly that won’t help, but if the problems are caused when the compressor kicks in, then disconnecting the power should solve the problem. She’ll have no A/C until it’s fixed properly, but that’s a better option than no power steering.

It should, in theory, be a fairly simple plug to pull so it’ll be quick and easy to find out.

Just to clarify … The belt is always under tension and (absent malfunction) all pulleys always turn. Nothing should ever slip. This is not /U] like a belt on a lawnmower where you engage the drive by pulling things taught and the belt stops slipping & starts pulling.

The A/C clutch is more like the clutch in a manual transmission. The pulley side is always turning and when the clutch engages the motion is transmitted through the clutch to start turning the other side where the A/C compressor is attached. And when the A/C is off or the compressor is not needed, the clutch freewheels while the compressor sits stationary.

This may sound like pedantic nitpicking, but IME this stuff is hard enough to picture over the phone without starting with a defective mental model of what the other guy is describing.

If the malfunction is the that A/C compressor is seized or nearly so, or the clutch is seized or nearly so, that will cause belt slippage which will fail the belt in very few miles; at most dozens - definitely not hundreds.

That has the look of being gleaned from a Chilton’s manual that’s probably “Mazda compact cars 1978-2009” or something so it has belt routings for a bazillion different cars and engines.

I’m 99% sure on this car the main belt runs the AC, PS, and alternator*. So if it does completely snap, you should be able to drive it a short distance before it runs out of electricity. It should be controllable without PS. However, when the belt snaps it’ll whip around the engine compartment and possibly break some other stuff, so if you do have to drive it a short distance it may be preferable to just take the belt off.

If you were wanting to cheap out, you can often buy a belt for a non-AC version of the car and simply bypass the AC compressor. That might be a better proposition in October than June though

*The only rub is that on some cars it might also run the water pump, which you shouldn’t drive more than a few hundred feet without. On most Japanese cars of this vintage it’s run by the timing belt instead of the accessory drive belt, though.

Assuming it has the 2.0 liter engine, it has two drive belts: one for the water pump and alternator, and one for the power steering pump and air conditioning compressor.

If the belt only screeches/burns when the A/C is engaged, the compressor is seized but its clutch is okay. The symptom can be avoided by making sure the A/C is not turned on.

If it screeches burns with the A/C off, the clutch is faulty, and the compressor may be seized as well. If it’s not fixed it will fix itself by shredding the belt. This will disable the power steering.

Power steering doesn’t make much difference at road speeds. Lane changes and curves shouldn’t be a problem. At slow speeds, it makes a significant difference. Parking lot maneuvers can be a challenge. City street turns will require extra effort but should be manageable for most people.