Heater draws down alternator

Hi all

I have a problem with my dads Cherokee. When ever he turns on the heater it draws the charging system down from 14.1v to around 12.89 13v. My dad took it to a battery shop and they put a new alternator and battery in it and it didn't change a bit. I swaped the blower motor and resistor out of mine. This also didn't work. I have been searching on here for a few hours but I suck at search and have found no results. Any help would be great.

Thanks:
David

I also forgot to say that he can turn on all the lites rear defrost and wipers it's fine. It only happens when the heater it turned on by it self or with the other stuff.

uhh i dont think that is a problem..mine and the 6 other cherokees i know of all do the same thing..

Should be ok, probably the gauge reading low more than anything.

have you checked it with a meter and verified the gauge?

Yes readings have been made with a fluke meeter.

I don't think gauge accuracy is a factor here. He is talking about a change relative to other electrical drains.

I don't know if I would say it's "normal" but it probably is not unusual when you are talking about only one volt or so. For what the anecdotal evidence is worth, my 93 doesn't exhibit a voltage drop when turning on the heater. I wouldn't be too concerned if every thing works properly and you are not smelling anything burning, blowing regular fuses, melting parts or blowing thermal fuses in the resistor pack. Otherwise I would start checking the switch, cleaning connections and/or upgrading wire size. Also, are you sure your blower motor that you swapped in is up to spec?

What year?

Renew your cable connections and grounds.

Common, symptoms include slow flashers, slow wipers, dimming headlights.

Pelican said:

Also, are you sure your blower motor that you swapped in is up to spec?

What year?

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Not sure about up to spec but they both bench test/run fine.

my dads is a 95 the used blower motor is out of an 89.

joe_peters said:

Renew your cable connections and grounds.

Common, symptoms include slow flashers, slow wipers, dimming headlights.

Click to expand...

I told him the same thing, the pos+ wire going from the battery to the starter looks like crap. He did go around and clean what grounds he could get to.
I will get him go go buy some new cables and see what happens

Thanks

Get good quality cables, low gauge and higher strand count.

You say you've verified the readings, but not where you took them. Make sure you take readings at the battery. The heater blower will drop the voltmeter, especially on older XJ's, without actually dropping charging voltage, as others have mentioned, and it may also drop a reading from the dashboard or the lighter socket. Does turning on the heater dim the headlights?

I see that the vehicle is a 95. Remember that using defrost will turn on the AC compressor, so belt slip could be contributing if it happens then.

Matthew Currie said:

You say you've verified the readings, but not where you took them. Make sure you take readings at the battery. The heater blower will drop the voltmeter, especially on older XJ's, without actually dropping charging voltage, as others have mentioned, and it may also drop a reading from the dashboard or the lighter socket. Does turning on the heater dim the headlights?

I see that the vehicle is a 95. Remember that using defrost will turn on the AC compressor, so belt slip could be contributing if it happens then.

Click to expand...

I took the readings from the battery I also installed a new belt thinking the same as you(belt slip). Also turning on the heat does in fact dim the headlights. But I did just get off the phone with my dad. He told me that it seams to be random. He started it this morning and all was fine with the defrost/heater on low med or high. Then later in the day was headed home and it started discharging or charging very low. He is using the dash gauge and one of those plug in the lighter digital meters.

At this point I think it's his age. He's 70 years old anal and board out of his mind. I think he's making up problems to keep his mind busy and me! He use to be a shop superintendent for a large company where he was alway figuring ways to repair things for 42 years. I'm also thinking he is reading dc like he wold ac that it should always be the same no mater where you are in the building.

Dave

But I am going to make some new battery cables this weekend because it does need them.