Serpentine belt thrown twice on a 1988 C1500 5.7 350 Silverado

[Schurkey]

when "Defrost" setting is selected the compressor still turns on to keep things lubricated in the off season.

A/C runs in "Defrost" to chill the air, which dehumidifies it. Then it's re-warmed. Makes it more efficient at clearing the windshield.

Has NOTHING to do with "lubrication".

And of course, the A/C won't run if the temperature is so low that the refrigerant charge pressure is below the low-pressure switch cutout, to prevent compressor damage. But by then, it's so cold out that the air doesn't carry much humidity anyway.

 

[Jeff Janssen]

A/C runs in "Defrost" to chill the air, which dehumidifies it. Then it's re-warmed. Makes it more efficient at clearing the windshield.

Has NOTHING to do with "lubrication".

And of course, the A/C won't run if the temperature is so low that the refrigerant charge pressure is below the low-pressure switch cutout, to prevent compressor damage. But by then, it's so cold out that the air doesn't carry much humidity anyway.

Makes sense... much more sense than my reason for running the A/C in DEF during the off season....

 

[Slade88]

I replaced the tensioner and idler pulley and belt. I started it up and it’s still walking off. It walks off one rib on the crank pulley on the left side, the AC was off when this happened. What on earth could it be? Is there any way I can definitely tell instead of firing off the parts cannon? Thank you!

 

[Schurkey]

Grab a straightedge--or a reasonable facsimile such as a carpenter's level.

Verify pulley alignment. The crank pulley is the "master". Check from the crank pulley to every other pulley especially the ones the ribbed side of the belt rides on--A/C compressor, Alternator, PS. The non-ribbed side seems to be less important, within reason. If the crank pulley is where you first see the belt going off the edge, I'd be looking hard at the previous pulley which may be the non-ribbed water pump.

Then check from the A/C, alternator, PS back to the crankshaft pulley. Pulleys can be out of spec in three dimensions (or in combinations of the three dimensions) so you have to check both ways to catch some problems.

Verifying pulley alignment the right way is NO FUN. It's an outright PITA, but it seems your vehicle is a problem-child. You may need to pull the fan shroud and fan for access to the pulleys.

 

[454cid]

I replaced the tensioner and idler pulley and belt. I started it up and it’s still walking off. It walks off one rib on the crank pulley on the left side, the AC was off when this happened. What on earth could it be? Is there any way I can definitely tell instead of firing off the parts cannon? Thank you!

Is the crank pulley wobbling?

What is on that side?

Do you have the large steel bracket with smaller braces bolted here and there? They can crack. If that's the case, it seems reasonable to me that thing may not line up.

 

[Slade88]

Is the crank pulley wobbling?

What is on that side?

Do you have the large steel bracket with smaller braces bolted here and there? They can crack. If that's the case, it seems reasonable to me that thing may not line up.

I’ll have to check for those brackets today

 

[Slade88]

Grab a straightedge--or a reasonable facsimile such as a carpenter's level.

Verify pulley alignment. The crank pulley is the "master". Check from the crank pulley to every other pulley especially the ones the ribbed side of the belt rides on--A/C compressor, Alternator, PS. The non-ribbed side seems to be less important, within reason. If the crank pulley is where you first see the belt going off the edge, I'd be looking hard at the previous pulley which may be the non-ribbed water pump.

Then check from the A/C, alternator, PS back to the crankshaft pulley. Pulleys can be out of spec in three dimensions (or in combinations of the three dimensions) so you have to check both ways to catch some problems.

Verifying pulley alignment the right way is NO FUN. It's an outright PITA, but it seems your vehicle is a problem-child. You may need to pull the fan shroud and fan for access to the pulleys.

The two pulleys that connect the belt to the crank pulley would be the ac pulley and the water pump. Should I replace those or just unbolt them and bolt them back on tight? I’ve removed pulleys before and they seem to just bolt on one way with not much room for changing the angle

 

[454cid]

I’ll have to check for those brackets today

Then I don't think you're understanding what I'm saying. Everything on the front of the engine except for the water pump is held on with a system of brackets. It'll either be a large steel bracket that pretty much covers the whole front of the engine with a couple small supporting brackets, or a couple of cast aluminum brackets, with possibly a few small steel brackets helping to support indiviual items like the alternator.

 

[Erik the Awful]

Grab a straightedge--or a reasonable facsimile such as a carpenter's level.

Yup. We went through this at the race track during a race with our BMW. A guest mechanic had done some work and "aligned" our power steering pump on an aftermarket bracket. I had to realign everything with a ruler and a handful of washers.

With the engine running, look at the pulleys and ensure nothing has a wobble. If it's all good, work from the crank pulley outward to the furthest pulleys. Use the ruler to ensure the pulleys are flat with each other. Keep an eye on the thickness of the outside edge of the pulleys in case one has a thicker lip. If they're the same thickness, the ruler should lay flat across both pulleys.

 

[Slade88]

Took it to my buddy’s shop, my power steering pump was missing a bunch of its bolts that connect it to the brace causing it to move around and the belt to come off.

All the other bolts to the accessory bracket were way loose, so we covered them in lock tight and added some lock nuts as well. We think this happened because the alternator supporting bracket was missing, and a couple other brackets appear to be missing as well. Only about 1 or 2, that I left in the tool box during a cam swap.