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A.c. / Alternator Problem 02 Silverado 5.3

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gmchevroletruck Enthusiast

gmchevroletruck

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Have done plenty of work on cars, but not a mechanic by trade...looking for some advice as to diagnosis and repair of the following problem: Truck has 130k, replaced battery in February, haven't driven more than maybe 2k since then. Alternator went out the other day - started truck and battery light was on, and voltage was down, then it just went back to normal for a short bit but it didn't stay long. Steadily went down over the course of the day while driving and ended up with me coasting into the driveway with a completely dead truck from lack of electrical power. Had the alternator tested at auto parts store, it was bad of course, replaced it today, also swapped the already new battery for another new one (just to be sure-it was under 2yr free replacement, so why not?). Started truck, it ran a bit weird at first but i think maybe because i was wetting the plugs pretty bad from the last drive, where i had very little power to even spark it. Ran the truck for a bit, tested with all accessories on to be sure the charging system was ok now, and found this: it will run everything at once, and i mean everything (brights, fan on high, radio, wipers on high, high beams, rear defrost, interior lights), but as soon as I hit the "a.c." switch, the voltage drops significantly and so do the rpms - one time it even killed the engine. Tested several times, same result. A.c. had been working fine. I cut the belt to the a.c. compressor and re-tested, no voltage drop. Am I correct in assuming that the a.c. problem is what killed my alternator to begin with, and more importantly, what is the a.c. problem likely to be? A bad clutch? Keep in mind it doesn't do it now if I press the a.c. button but I'm guessing all that button does is try to activate the clutch which isn't spinning anyway...and if I grab the a.c. compressor pulley I can spin it with my hand very very easily, no noises noticed that I can remember. If it's the clutch, or bearings, etc, can I fix this without spending $360 plus on a new compressor, or what would you recommend? Not wanting to spend money I don't have to, but don't want to do it twice either....

bill190 Enthusiast

bill190

Posted
Posted

When you say you cut the belt to the A/C, what does that mean?

 

Did you take a knife and cut the fan belt off?

 

Did you cut the electrical wire going to the A/C compressor?

 

Or just disconnect the A/C compressor wire at the connector?

 

If you just electrically disconnected the wire going to the A/C compressor and the problem went away, then there could be a short to ground in the A/C compressor clutch. Or the wiring on the compressor/clutch.

 

In some cases you can replace just the electric clutch portion rather than the entire compressor.

gmchevroletruck Enthusiast

gmchevroletruck

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When you say you cut the belt to the A/C, what does that mean?

 

Did you take a knife and cut the fan belt off?

 

Did you cut the electrical wire going to the A/C compressor?

 

Or just disconnect the A/C compressor wire at the connector?

 

If you just electrically disconnected the wire going to the A/C compressor and the problem went away, then there could be a short to ground in the A/C compressor clutch. Or the wiring on the compressor/clutch.

 

In some cases you can replace just the electric clutch portion rather than the entire compressor.

 

Thanks for the response, much appreciated.

 

I literally cut the a.c. belt off the pulley (used hose cutters).

 

Left the wire hooked up to the compressor.

 

So, with the belt off and the switch on, no excessive current draw or load, but I suppose that is to be expected because without the pulley spinning, I would think the switch does nothing anyway? (doesn't it need the inertia of the spinning pulley to help pull the clutch in, or...?) What I'm also not sure of is, if it is mechanical load (i.e., compressor locking up) that was pulling the rpms and voltage down, or if it was an electrical draw that was pulling the voltage down (and even killed the engine once). I could describe it like this: turn a.c. on, immediate noticable voltage drop at idle (down from about 14.5 to maybe 11-ish), and slight idle speed reduction...turned off a.c. and repeated process a few times, one time it killed the engine. But, as I turned the a.c. pulley by hand (with the belt off and the a.c. switched off ) it was very easy to turn.

 

With the belt off, can I tell if it's the compressor locking up, by: turning the a.c. switch on, and attempting to turn the pulley with the clutch "engaged"? Or, will the clutch not engage unless it's spinning anyway?

bill190 Enthusiast

bill190

Posted
Posted

Basically the A/C compressor electric clutch is either on or off. I can't see where the compressor operating would make it draw more electricity.

 

It is possible that it has a short and the short only happens when the compressor is spinning or spinning fast.

 

If there is a short in the A/C compressor (and it is drawing too much electricity), a fuse should blow or a fusible link should blow. Be sure there is a fuse for the A/C compressor and that it is the correct amperage for the circuit and not more amperage than should be there or bypassed.

 

Then to test this, you could connect an amp meter in series with the A/C compressor and see how much amperage it is drawing - with belt and without belt.

 

So far as the A/C compressor locking up and slowing down the engine, probably the best way to test this would be with A/C gauges on the high and low pressure side, and amp meter on the compressor clutch wire (to be sure that was not drawing to much amperage and was not the problem), and watching the gauges and the engine speed.

98 Z71 SLT Senior Enthusiast

98 Z71 SLT

Posted
Posted

First of all, you are over-loading the entire electrical sytem in that truck by running ALL options at once...give us a scenario where you actually have to run everything at once...not gonna happen.

 

Second, there is nothing wrong with your truck. You just got all paranoid when it stalled, and you made it stall out. Put a new A/C belt back on it.

 

Lastly, your THROTTLE BODY needs a cleaning. Why? When these TB's gum up with carbon, idle speed drops. Lower idle speed = lower alternator output = overloaded electrical system = scared owner = money wasted.

CapitalTruck Senior Enthusiast

CapitalTruck

Posted
Posted

A truck should be able to run all of it's accessories:

 

Dark rainy night where defrost and rear defogger is needed:

 

Headlights, Windshield wipers, blower (with compressor), rear defogger, putting on interior light to look for toll money, putting window down (power windows) to pay toll. This doesn't seem out of the realm of possibility. I'd raise holy heck if a mechanic told me I shouldn't be able to do all of this. My truck can do all of this with no problem. (I had a problem with it earlier, tightened battery terminal bolts and new we're cool in the gang). Don't be calling people paranoid when their truck stalls, drivers don't like it when that happens.

gmchevroletruck Enthusiast

gmchevroletruck

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First of all, you are over-loading the entire electrical sytem in that truck by running ALL options at once...give us a scenario where you actually have to run everything at once...not gonna happen.

 

Second, there is nothing wrong with your truck. You just got all paranoid when it stalled, and you made it stall out. Put a new A/C belt back on it.

 

Lastly, your THROTTLE BODY needs a cleaning. Why? When these TB's gum up with carbon, idle speed drops. Lower idle speed = lower alternator output = overloaded electrical system = scared owner = money wasted.

 

Ok, I do appreciate the input and the help, but I would almost bet there is something massively wrong with the a.c. system. This is not my first time working on vehicles, although as I said, I'm not a professional mechanic by trade, and don't claim to know everything by any means, but I do know enough to know there is a problem, I'm just on here to get help finding out what it is. Let me just clarify, in hopes of making it make more sense what I was doing, and what was happening. Agreed, there is almost never a scenario where you will need to run all the accessories at once on any vehicle, but as I stated, my reason for doing so, was to test to be certain that my charging system was up to par after I had just installed a new alternator and battery. I would never overload the vehicle and continue operating it in this fashion, it was a temporary test of the charging system's strength, and was just for a short (few second) period of time. I did discover that there is a major problem with the a.c. system, because, even with every other accessory off, when the a.c. is turned on, it bogs the car way down. I'm not describing the typical idle flucuation when the a.c. is turned on in a vehicle, i'm talking about: the idle speed went down so far that the engine almost stalled, and did in fact stall completely once. And when the a.c. was turned on, with every other accessory off, the voltage gauge went from about 14.5 down to...way lower, I'd have to look again to be sure but somewhere in the 10-11 range or so...it was way lower than I had ever seen it while running the vehicle - it usually barely budges at all no matter what is running, and even barely budged when I had the following running: brights, wipers, cd player, interior lights, and fan on high (no a.c. on at that time). It wasn't until I turned the a.c. on, even with all the other accessories turned off, that the voltage and idle dropped very significantly, and very abmormally.

 

Again, I want to clarify that I am by no means trying to argue with you, just trying to make it more clear what I was attempting and why, and clarify some of the details of what was happening. I appreciate the advice, and am not here to argue with anyone, just to help and be helped, and enjoy chat with fellow GM owners, etc.

 

Incidentally, I do have a new a.c. belt already, and if you think I should put it on after all of that being said, I will try that. I did notice that the truck seems to run a tad bit less smooth after the "running it with low voltage till it died to get home" incident when the alternator was dying, and when I took the intake hose off, did notice that the throttle body indeed had carbon in it...Thanks for the advice and I will clean that as well, and it probably needs plugs

gmchevroletruck Enthusiast

gmchevroletruck

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Basically the A/C compressor electric clutch is either on or off. I can't see where the compressor operating would make it draw more electricity.

 

It is possible that it has a short and the short only happens when the compressor is spinning or spinning fast.

 

If there is a short in the A/C compressor (and it is drawing too much electricity), a fuse should blow or a fusible link should blow. Be sure there is a fuse for the A/C compressor and that it is the correct amperage for the circuit and not more amperage than should be there or bypassed.

 

Then to test this, you could connect an amp meter in series with the A/C compressor and see how much amperage it is drawing - with belt and without belt.

 

So far as the A/C compressor locking up and slowing down the engine, probably the best way to test this would be with A/C gauges on the high and low pressure side, and amp meter on the compressor clutch wire (to be sure that was not drawing to much amperage and was not the problem), and watching the gauges and the engine speed.

 

Thanks for following the thread, Bill, the advice is appreciated.

 

I was wondering that too, as far as the compressor making it draw more electricity...mechanical drag on the pulley maybe, and I've seen that on my other truck when the compressor went bad a while back.

 

As for the spinning speed issue...it was at idle that it first did it, although if I remember correctly, even when it bogged down, and I tried to rev it to compensate, the voltage was still down way lower than normal, not even close to being normal. I'll have to put the new belt on (needed to be replaced anyway) and test again to be sure.

 

I'll have to put a belt back on and do the tests you suggested...I have the gauges for 134a, etc...and a meter, although it doesn't do d.c. amps, just ac amps (I do H.V.A.C. for a living, ironically, and am vaguely familiar with automotive a.c. but for some reason this just threw me for a loop and I was thinking of it more as an automotive electrical problem, which I am not as comfortable with, but it may not be)

 

Thanks for the advice, and I will put the belt on and test with the above...as soon as it stops raining here!! :lol:

gmchevroletruck Enthusiast

gmchevroletruck

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A truck should be able to run all of it's accessories:

 

Dark rainy night where defrost and rear defogger is needed:

 

Headlights, Windshield wipers, blower (with compressor), rear defogger, putting on interior light to look for toll money, putting window down (power windows) to pay toll. This doesn't seem out of the realm of possibility. I'd raise holy heck if a mechanic told me I shouldn't be able to do all of this. My truck can do all of this with no problem. (I had a problem with it earlier, tightened battery terminal bolts and new we're cool in the gang). Don't be calling people paranoid when their truck stalls, drivers don't like it when that happens.

 

Thanks for the post. Yes, I thought so as well, and seems I may have been driving in that exact scenario in the past, in this truck, and remember looking at the volt gauge (I'm a gauge person), and being pretty impressed with the truck's ability to run whatever I needed at the same time. My older (94)GMC 2500, on the other hand, has a whole other issue that I'm not ready to tackle till I get the good truck (the one I described on the thread) back to normal - it also has a new battery, new alternator, good clean cables, tight connections, and seems to be running everything ok, but the volt gauge starts at about 14 when you start the truck, and steadily declines till it reaches a point when you're driving at night with the headlights on, the gauge reads below normal, somewhere in the 10-ish range approximately - I'd have to go count the hash marks and drive it again, but it's seriously not looking right on the dash. And if I have the trailer hooked up and turn the flashers on, it blows a fuse. But, that's another issue for another day lol...always something, as they say.

gmchevroletruck Enthusiast

gmchevroletruck

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First of all, you are over-loading the entire electrical sytem in that truck by running ALL options at once...give us a scenario where you actually have to run everything at once...not gonna happen.

 

Second, there is nothing wrong with your truck. You just got all paranoid when it stalled, and you made it stall out. Put a new A/C belt back on it.

 

Lastly, your THROTTLE BODY needs a cleaning. Why? When these TB's gum up with carbon, idle speed drops. Lower idle speed = lower alternator output = overloaded electrical system = scared owner = money wasted.

 

Where are you from, in Wisconsin? I was born there, and still have family there...visit occasionally. Used to live in Madison, Milwaukee, Janesville, and West Bend, still have family in Janesville (shame what's happening there), and West Bend (just visited on Easter)...I live in Memphis now, though.

gmchevroletruck Enthusiast

gmchevroletruck

Posted
  • Author
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A truck should be able to run all of it's accessories:

 

Dark rainy night where defrost and rear defogger is needed:

 

Headlights, Windshield wipers, blower (with compressor), rear defogger, putting on interior light to look for toll money, putting window down (power windows) to pay toll. This doesn't seem out of the realm of possibility. I'd raise holy heck if a mechanic told me I shouldn't be able to do all of this. My truck can do all of this with no problem. (I had a problem with it earlier, tightened battery terminal bolts and new we're cool in the gang). Don't be calling people paranoid when their truck stalls, drivers don't like it when that happens.

 

You live in D.C? My wife just got back from taking her students there on a field trip (from Memphis)..."changing of the guard, eternal flame, capitol building, short white house tour, things I'm guessing you don't frequent when you live there, much like "Graceland" and the like, here lol.

bill190 Enthusiast

bill190

Posted
Posted
...I was wondering that too, as far as the compressor making it draw more electricity...mechanical drag on the pulley maybe, and I've seen that on my other truck when the compressor went bad a while back...

 

Hummm... That's a good possibility! Perhaps when the clutch is engaging, it is causing mechanical drag of some sort. I suppose it would make a bit of noise if this were the case.

 

Another thing I was thinking when reading your reply above, is if the engine is being slowed down by a mechanical load (like a locking up compressor), would that in itself cause the voltage to drop?

 

i.e. The question is: Would a very slow *running* engine for some reason cause the voltage to drop? If the alternator is operating very slowly, would this drag down the battery and become a huge load?

 

If this is the case, then maybe the problem is just a locking up compressor and the electrical problems were a result of the engine running very slowly? (I don't know???)

gmchevroletruck Enthusiast

gmchevroletruck

Posted
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...I was wondering that too, as far as the compressor making it draw more electricity...mechanical drag on the pulley maybe, and I've seen that on my other truck when the compressor went bad a while back...

 

Hummm... That's a good possibility! Perhaps when the clutch is engaging, it is causing mechanical drag of some sort. I suppose it would make a bit of noise if this were the case.

 

Another thing I was thinking when reading your reply above, is if the engine is being slowed down by a mechanical load (like a locking up compressor), would that in itself cause the voltage to drop?

 

i.e. The question is: Would a very slow *running* engine for some reason cause the voltage to drop? If the alternator is operating very slowly, would this drag down the battery and become a huge load?

 

If this is the case, then maybe the problem is just a locking up compressor and the electrical problems were a result of the engine running very slowly? (I don't know???)

 

 

That is a good point, although I seem to remember that when it was trying to stall out, even when I increased the rpms by throttle, the voltage stayed down when the rpms were up. But again, I will have to put a belt back on and repeat the process to be sure of that...the next step will be doing that, and the tests you recommended earlier (and cleaning the throttle body, replacing the plugs). Once I do those tests with amp draw while watching the refrigerant gauges, it should tell more of the story (good idea, thanks)...now I just have to find the time to do it very soon

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