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As of today i am new to the forum (lots of great information on here) I bought my first jeep just over a year ago and have loved every minute of it. Its a 2000 XJ with 120,000. I am now having a problem when i have the heat on, when the heat is on it discharges to around 12-13, but when i turn it to either of the defrost settings it discharges nearly all the way and says check gauges, my headlights dim, and the stock stereo turns off display and all. It will do this off and on. The only way to get it to quit is to turn the heater all the way off. Its been doing this about a month and has killed my battery. My only suspect is maybe the blower motor is bad and is drawing too much power? When a bought it i replaced the serpentine belt with a Gatorback and it is on there very tight so i don't think its slipping. Any help would be much appreciated.
 

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Discussion Starter #4
when the problem first started it would chirp, sounded like it was on the drivers side. it has progressively gotten worse (the draw) and lost most to all of the sound.
 

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1) Check the tension on your belt - it may be loose. Buying a Krikit II belt tension gage from NAPA is a good idea.

2) I'm assuming this happens at idle - if you turn your heater on and you note the voltage drop, try just running your crankshaft speed up to 1100-1200rpm or so. That should bring it up - indicating that you're either having a much heavier draw from your blower fan, or that your alternator output is dropping for some reason (indicating replacement.) The blower fan is a fairly high-draw item, especially at higher speeds.
 

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Discussion Starter #7
1) Check the tension on your belt - it may be loose. Buying a Krikit II belt tension gage from NAPA is a good idea.

2) I'm assuming this happens at idle - if you turn your heater on and you note the voltage drop, try just running your crankshaft speed up to 1100-1200rpm or so. That should bring it up - indicating that you're either having a much heavier draw from your blower fan, or that your alternator output is dropping for some reason (indicating replacement.) The blower fan is a fairly high-draw item, especially at higher speeds.

It actually seems to do it more under normal driving. When i am driving it and it discharges i gas it up a lot trying to spin the alternator more but it doesn't help. it happens randomly. it will draw all the way down and the air barely blows then kicks back to 14 exactly and all it fine. the only thing that will make it stop is to turn the air all the way off. when i first bought the truck i noticed when defrost is on and i am idling the motor goes from 600 rpm to about 800 off and on. I have read up on this and it seems it is normal to evacuate moister from the air ducts? I think this is the a/c clutch cycling on and off. It is definitely worst while this is happening.
 

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The AC will cycle on and off any time you're using either of the modes that involve the defroster, as the compressor is being used.

I'm still not too clear on if you're getting any noises. I mean are you getting horrible screeching noises when you increase throttle from a stand-still or when you're idling and turn the heater/defroster on? If you are, then your belt needs to be tightened more.

Also, if youv'e recently installed a new belt, it will loosen and gain some play over time. This is normal because new belts will stretch, which can lead to the problems you're having. Remember, use the Keep It Simple (KIS) method. Start with the easy then work towards the difficult/more expensive possibilities.

If your belt is loose enough, you will notice a significant loss in power.

A new belt should be tightened to 180-200 lb-ft of tension, and a broken-in/used belt should be tightened to 160-180 lb-ft of tension. You can check the tension by checking how much play is in the belt. If the belt can deflect .5" or more between the longest stretches between pulleys, then it's too loose, and you must tighten it.
 

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It finally screeched at me tonight when it was idling. It did every time the compressor kicked on then stopped once it kicked off. I could also smell rubber when it was doing this. I couldn't pinpoint the noise since it was so loud but I'm almost positive its coming from the compressor. And for the belt it flexes about that much, more then it did a weak ago when i checked it last. I'm gonna try and tighten it a bit more tomorrow. It never made noise before so i didn't really think it was the belt. Now that it did I'm pretty sure this is the problem. Hopefully the weather holds off. Thanks for everyone's help and ill let you know how it turns out.
 

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You would be amazed on how little a change in tension on these belts makes. My '98 did the same thing and it was literally about 3 full turns of the adjuster to get it back to normal. If that doesn't help you, bring it somewhere to get a charging syst. check. You could pull the alt and get it checked, but if you went thru half the work already, you might as well replace it....

So...
Tighten belt, then get a charging system check.
 

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You would be amazed on how little a change in tension on these belts makes. My '98 did the same thing and it was literally about 3 full turns of the adjuster to get it back to normal. If that doesn't help you, bring it somewhere to get a charging syst. check. You could pull the alt and get it checked, but if you went thru half the work already, you might as well replace it....

So...
Tighten belt, then get a charging system check.
Yes i am amazed... Did about what you said about 4 turns tightened everything back up and my problem is gone. I think the reason this happened is because a couple of weeks ago when the belt was chirping i put some belt dressing on it to see if it would help, it didn't but i think that softened the belt up some and allowed it to stretch more. Thanks for everyone's help.
 

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Here to revise an old post I'm having similar issues except my belt is tight and I have no noises accompanying but when the fan is turned on voltage drops to around 12 fan off jumps to around 14 I can blast the radio with my sub and amp cranked to the max high beams on and voltage hardly changes turn the fan on and instantly drops have been chasing headlight issues where they flicker on and off after a bit found a corroded plug cleaned it all up and thought it went away until I turned the fan on and now it does it again every time the fan is running for more than a few minutes I replaced the fan and I know the resistor needs replaced cause the fan only runs on high which doesn't bother me but associating the fact that heater fan on and headlights not working does bother me any suggestions?
 

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Are you talking about your heater blower ( fan)? The power for that blower comes through the ignition switch. Check your connectors on the steering column. Also, put a volt meter on battery and confirm the volt gauge is accurate.
 
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