Texas Heat, AC and Battery Drain

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Topic author
MilesTexas
Posts: 38
Joined: Fri Apr 01, 2022 7:59 am

Texas Heat, AC and Battery Drain

Post by MilesTexas »

Well, started driving around the Wag this summer. I put in a Sniper and it is still going through the final learning phases. I drove around my neighborhood - keeping it under 50. Start, stops, hard acceleration..etc. It was already 90 degrees yesterday, so I had my AC full blast (and it wasn't very cold, need to recharge but thats another thread)

When I finished I like to turn my truck off, wait two minutes and start again. Simulate I went into the coffee shop or something. It was a nightmare when I first bought it and left me stranded multiple places. When I did it yesterday, the engine dragged and then finally turned over and started. Had it not been a sniper, it wouldn't have started. But also, the engine had fuel primed and ready. I am worried after that ride, if I tried to start late that day and the fuel bled back. It wouldn't start, battery was reading 12.1 and slowly dropping as I turn the key over.

My question is, should the battery always drain down if I am going below 50 and using AC on full? I upgrade to the 90amp Alternator and thought that should solve all charging problems. No crazy electronics and if anything, I will be adding the original fog lamps back. Maybe more stereo

Texas is always going to be hot, so the AC full blast will probably be every time I drive
84 Jeep Grand Wagoneer, Future Daily Driver?
- Original AMC360 w/ HEI dist (del Coil, ECM)
- Holley Sniper
- Original AC/Heat
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tgreese
Posts: 7117
Joined: Fri Jun 08, 2012 6:31 am
Location: Medford MA USA

Re: Texas Heat, AC and Battery Drain

Post by tgreese »

Do you have a voltmeter on the dash? The alternator should maintain 13.5-14 volts while you are driving. If you have an ammeter, it should stay at zero or slightly in the charge region always. Only discharge while starting, then very positive while the alternator makes up the deficit from starting.

More likely a failing battery IMO. Parts store will check your battery for free. That would be my first response. I have a digital checker, check the battery and track the CCA rating at least every year. AS your battery fails, the CCA rating will go down and eventually the checker should register "bad."

Also, if you have an ammeter, it's not safe with an oversize alternator. You don't want a dash fire.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 Chryco Jeep Cherokee KL Trailhawk, ECO Green
Blockchain the vote.

Topic author
MilesTexas
Posts: 38
Joined: Fri Apr 01, 2022 7:59 am

Re: Texas Heat, AC and Battery Drain

Post by MilesTexas »

I do not have voltmeter on dash and I bypassed the original ammeter. How would I check the CCA? I have a volt meter gauge but I have no experience checking that.
84 Jeep Grand Wagoneer, Future Daily Driver?
- Original AMC360 w/ HEI dist (del Coil, ECM)
- Holley Sniper
- Original AC/Heat
User avatar

tgreese
Posts: 7117
Joined: Fri Jun 08, 2012 6:31 am
Location: Medford MA USA

Re: Texas Heat, AC and Battery Drain

Post by tgreese »

Buy a tester. https://www.amazon.com/s?k=car+battery+ ... _sb_noss_2

Or ask your local parts store to test it. Usually they will do that - in hopes of selling a battery.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 Chryco Jeep Cherokee KL Trailhawk, ECO Green
Blockchain the vote.

Topic author
MilesTexas
Posts: 38
Joined: Fri Apr 01, 2022 7:59 am

Re: Texas Heat, AC and Battery Drain

Post by MilesTexas »

Ah gotcha, got one ordered. Thought there might be some magic I could do on a multimeter.

Not sure if it adds anything to the discussion but I put truck in park and let it idle with AC on full. The battery was slowly ticking down. Bout .01 every 15-30 seconds. So 14.18 - 14.17...etc

Unless the battery is bad, I just assumed that this larger alternator could handle this type of pull. Can't imagine at night with all lights and AC and Radio... would die pretty quick
Last edited by MilesTexas on Tue May 09, 2023 11:19 am, edited 1 time in total.
84 Jeep Grand Wagoneer, Future Daily Driver?
- Original AMC360 w/ HEI dist (del Coil, ECM)
- Holley Sniper
- Original AC/Heat
User avatar

tgreese
Posts: 7117
Joined: Fri Jun 08, 2012 6:31 am
Location: Medford MA USA

Re: Texas Heat, AC and Battery Drain

Post by tgreese »

Nope - there is some specialized circuit inside the tester that looks at ... something. Voodoo. The old-fashioned type testers used a whomping big resistive load and measured the voltage drop (load testing). Modern electronic types do some kind of small-signal response analysis, using the battery voltage itself to power the meter.

I'd agree that your alternator should be able to handle all normal loads, ie AC, lights, etc all at once. Could be a bad alternator but I'd rule out the battery first.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 Chryco Jeep Cherokee KL Trailhawk, ECO Green
Blockchain the vote.

rocklaurence
Vendor
Posts: 2565
Joined: Sat Mar 30, 2013 6:53 am

Re: Texas Heat, AC and Battery Drain

Post by rocklaurence »

Make sure that your alternator belts are tight and not slipping. Also, in my case the volt meter lies and shows a volt lower than it is. My AC on max in Florida shows on the dash as 12-12.5 but at the battery with a meter it shows 13-13.5vlt.
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