AC power drain

[jxavierf]

Voltage is usually btwn 12 and 14 without AC......once I turn the AC on, needle drops to the red at the last tick/line. Is this normal? Alt is new, battery is reading 12.49V with with engine off and key in ignition at half turn.

 

Thanks.........

[NorthWet]

Nominal voltage for a "12 volt" car battery is 13.2 volts. When the car is running/charging it should be about 13.5-14.5 volts. If just turning on the A/C (what blower setting? also, idling or above idle?) drops your voltage that far, then you have probably have either an alternator issue of a wiring/bad-connector issue. Or, if this is happening just at idle, you may have loose/worn/slipping drive belts. If this is at idle, does the idle speed drop significantly?

[jxavierf]

The V are is only dropping at idle.....without the AC on the car at ilde reads around 12V and with the AC at idle maybe 6V (in the red at the first dash). Not much of a difference at what AC setting. Once I accelerate with the AC on, the V's rise to normal around 12V....at around 50mph closer to 13V. Bear in mind that the Alt is only 5 months old.

 

Thanks

[Jerry DeMoss]

I have seen on some vehicles that when the a/c is turned on and the power drops quite a bit as with yours,there is a restriction in your a/c.Just a hunch but I would check the orfice tube in your a/c. Sounds to me that there is a good possibility that it is what is wrong with it. I am betting that the orfice tube is plugged, not letting the refrigerant circulate the way it should causing the compressor to over load and make the engine work extra hard,thus making the power drop. I hope this helps.

[KStretch55]

Hmmm, sounds like mine could be having a similar problem, though not to the degree his is. Where is the orofice tube and how do you clean it? Do I have to evacuate the system? Thanks

[NorthWet]

There is no (significant) direct connection between the A/C functioning and very low voltage. The A/C is engine driven, and its use would only put load on the engine and slow down the RPM. The only electrical use by the A/C system is for the compressor clutch (negligable) and the ventilation blower motor (would show same effect even if A/C not "on" but other setting selected).

 

The indirect effects would be caused by slowing the engine down and/or the drive belts slipping from the load and being too loose/worn.

 

12-13 volts is NOT normal voltage. Again, minimum voltage for a properly charged "12 volt" battery is 13.2 volts. This is at rest with no load/charge being applied. It is possible that your gauge is misreading, but unlikely if you are seeing a 6v reading.

 

Alternators, especially rebuilt ones, can be bad out of the box, or shortly thereafter. (A friend got 3 bad rebuilts in a row from a discount parts store.) "5-months new" doesn't mean much if it was a rebuilt.

 

That said, a healthy battery will not let the voltage sag to 6v with minimal load. What other electrical loads did you have on when you saw 6volts? headlights, wipers, 50000watt stereo ? A healthy battery should not let the voltage sag more than a volt or so below its current state of charge. (9-10 volts would be minimum "acceptable" reading for a battery with a failed alternator and a heavy electrical load, and 11-12 is more likely.)

 

My guess is that at this point you may have multiple problems. Alternator sounds like toast and the battery is on its last legs. OR, it could ALL be caused by bad connections. I would check the alternator's output voltage at the alternator; it should read around 14-14.5v, maybe higher. I would also check the battery's voltage right at the battery posts.

 

 

Semi-OT: The "orifice tube" in car A/C is more commonly known as an expansion valve. It varies the size of an orifice, and thus refirgerant flow, into the evaporator. Problems with it will be manifested as non-cold A/C air.

[Jerry DeMoss]

Yes you do have to evacuate the system or at least bleed off pressure to do it or you will end up doing what I have seen some people do and get sprayed with the extra pressure. It depends on what type of car you have as to where the orfice tube would be. I would say the best answer is to get a shop manual and check into the location of it.As for the cost of the orfice tube itself it should not cost you more than $10,but you will have to buy a couple cans of refrigerant to recharge it all. To make things easy on you when you want to recharge it just buy a recharge kit at the local auto parts store. I would recomend putting the can of refigerant (after everything is all hooked up and the engine is running) into a bucket of warm water.This makes the can charge the system better because you are pressurizing the system when recharging. As far as where you connect your hose to recharge also depends on your vehicle and what type of refigerant you have in your car. Most older cars have R12 and the newer ones have R134a . I hope this helps answer some questions you might have had.

[KStretch55]

In retrospect, I don't think I have a charging problem. My guage drops to about 12volts with A/C on, especially with the fan on High. But, who knows how accurate the guage really is, I should check at the battery with my voltmeter to be sure. However, the A/C system is charged and it doesn't seem to blow as cold as I think it should, so I may need to check further into the orofice valve mentioned.

 

 

Thanks

[jxavierf]

I'm guessing that its a bad connection/ bad ground causing these problems.......which leads to how to best check for bad grounds.....I have a voltmeter, though don't know how to use it in detecting bad grounds.

[ausubaru92]

Its got me stumped that the volts are only dropping at idle > which would make me think it was the alternator

But for it to drop that low with the ac would make me think there is a short in the compressor clutch circuit (stab in the dark)

It could also be bad grounding,... check all your negative straps between the motor, battery, chassis ect. for corrosion/loose connections

Get your voltmeter and test

1. between the battery negative and chassis,

2. then between the battery negative and engine block

3. then between the chassis and engine

 

all 3 should show 0 volts

 

if a voltage is obtained then you have a weak ground

 

Hope this helps

 

Gannon

[jxavierf]

Should I test all of this with the voltmeter with the car off or on?

[PoorManzImpreza]

stupid question but is the car idling up when you turn on the ac? tach should sit at just about 1100-1200 rpm with ac on and funtioning correctly..

[jxavierf]

No.....when I turn on the AC no change.....when I turn on the fan, thats when the RPMs drop (they drop about 150-200 rpms) and the voltage drops.

 

Q. I noticed that my positive terminal to the battery has its own ground.....a wire coming off the red terminal connected to the body........is that suppose to be there???

[Cougar]

I'm guessing that its a bad connection/ bad ground causing these problems.......which leads to how to best check for bad grounds.....I have a voltmeter, though don't know how to use it in detecting bad grounds.

 

To find a bad ground connection using the voltage drop method is easy to do. A good ground connection basically has zero volts of drop between the negative battery post (the reference point) and any other ground point on the car. When there is a bad connection to ground then that means there is resistance at the bad connection that shouldn't be there. The current in the circuit the ground wire is making the return path for has to pass through the resistance of the bad ground connection. The added resistance will cause a voltage drop across the bad connection and will cause some of the supply voltage to be taken away from the device that is supposed to be on. It is this voltage that you are trying to find. A good connection would be like a measuring the voltage across a piece of wire, which has no resistance, so there is zero voltage drop.

 

Your voltmeter in the dash is showing you there is a problem at idle at least. The meter should never get below around 12 volts though there may be some normal voltage drop between the meter and the battery to account for some of the loss. I would check for a problem with the wiring by looking at the voltage directly on the battery posts and the alternator output. They should be real close to the same and over 12.2 volts at idle with little load. Check the voltage with the AC on then and compare readings. If you have 12 volts there and the dash meter reads around 6 volts, then the trouble is in the wiring between the battery and the gauge. The problem may also be with the meter itself.

[jxavierf]

Thanks Glen...........

[Cougar]

Your welcome for the help. Let us know what you find out.

[NorthWet]

Regarding testing for bad connections by measuring voltage:

 

What you are looking for is high resistance connections, and the method you have chosen to use is measuring voltage DROP across a connection. In other words, you are using an indirect method of finding the problem, and you should understand this.

 

In order to get the indirect measurement of voltage, you also need for there to be current flow thorugh the wire/connection. A piece of unconnected wire has a resistance, but on its own it does not have a voltage measurement of any kind. You need current flow, and the measured voltage DROP across the wire will vary directly with the amount of current that it is conducting.

 

So, for the voltage test of connections to work, stuff needs to be turned on and drawing power for current to flow and a voltage drop to be developed. The more "stuff" that is drawing power the more current is flowing through the connections and the more obvious the voltage drop across the connections will be.

 

Short answer: You need to turn power-using stuff "on" in order to do a voltage drop test.

 

 

 

BTW, there is no way a shorted A/C clutch will draw enough power to drag down the system voltage that much UNLESS it is also pouring out smoke from extremely overheated wiring.

[ausubaru92]

Jxavierf, u said that there was no change in rpm when the ac is switched on?, that would tell me that the clutch isnt coming on. have somebody switch on the ac while you are watching the compressor, the front of the compressor with the 3 prongs stickin out should start to spin

 

Quote. I noticed that my positive terminal to the battery has its own ground.....a wire coming off the red terminal connected to the body........is that suppose to be there.

 

Where abouts is it connected to the body? there should be one thick cable going from the negative terminal to a lug beside the starter motor, and one thick cable going from the positive terminal to a connection on the starter motor and one thinner cable going from the positive terminal to a small plastic box (fusable links) mounted on the coolant resivior

 

And yes Northwet, there is no way a shorted A/C clutch will draw enough power to drag down the system voltage that much UNLESS it is also pouring out smoke from extremely overheated wiring,.... Unless there is a bad connection somwhere in the circuit, which would cause a voltage drop.

Gannon

[PoorManzImpreza]

No.....when I turn on the AC no change.....when I turn on the fan, thats when the RPMs drop (they drop about 150-200 rpms) and the voltage drops.

 

Q. I noticed that my positive terminal to the battery has its own ground.....a wire coming off the red terminal connected to the body........is that suppose to be there???

 

ok here's my theory..nothing electrical might be wrong with the car..your problem might be that your engine isn't idling up when you turn on your ac (ac small switch on and blower fan turned to 1-4) if your idle up solenoid and vacuum diaphram (carb. model) isn't functioning then when your ac turns on the engine idle will drop from it's normal 700-800 rpm to maybe 300-400 rpm..the alternator will NOT be operating fast enough to supply the correct voltage and current and the blower fan and electric radiator fan will only be adding to the load..if this is combined with a batt. that doesn't have all six cells inside of it functioning correctly you could easily replicate all your symptoms..If your car is carberetted I'd chech to see if the vacuum hose hasn't slipped out of the idle up diaphram mounted on the intake manifold next to the throttle linkage...and if it is that it is actually working and the solenoid that opens it to manifold vacuum is working as well..if it is EFI check the FICD solenoid on the throttle body it is behind the throttle body with respect to the engine...HTH..

[jxavierf]

Is this the vac. diaphram or idle up solinoid? See pic link below.............

 

Correction......the rpms drop from about 12.5V to around 9V in the red (not 6, like I said before).....and yes it only happens once I turn the AC air switch on (1-4) at idle....but goes back to 12V when I press the gas. I beleive the vac. diaphram or idle up solinoid is suppose to trigger an arm the pulls the throttle open more....I tested this and it doesn't move whether I have the AC on or not.... See pic below....

 

http://www.ultimatesubaru.org/photos/showphoto.php?photo=6362

 

Thanks..........

[NorthWet]

...

Correction......the rpms drop from about 12.5V to around 9V in the red (not 6, like I said before)...

This is STILL an abnormal electrical situation. I would strongly recommend that you troubleshoot and fix the electrical system problem(s) prior to "rearranging the deck chairs on the Titanic".

[jxavierf]

Ok.....I tested the voltage from the battery with a voltage meter.....at idle the positive terminal to chassi ground showed about 14.5V.....when I turned on the AC it read about 14.3V....negligable. However, in my car the guage was reading about 12.3V at idle and almost 12V with AC on......but this was in Park.....once I put gear into reverse or drive (automatic) the voltage droped to below 10V (in the red).....this only happened with the AC on, and once I press the gas the voltage goes back up to 12V ish. By the way I fixed the vac. or idle solinoid thingy......had a hose disconnected....so now when I turn on the AC the lever pulls the throttle so the idle only drops 100 or 200 rpms. I still think this is all wierd and that something is wrong. It seams that the V drop has more to do about being in gear than the AC. Any thoughts?

[PoorManzImpreza]

Idle shouldn't drop at all it should increase.. glad you found what I was talking about in my earlier post.

 

ok this vacuum diaphram can be adjusted just loosen the 8mm nut on the threaded shaft at the back of it and with the ac on adjust the threaded shaft with a screw driver. As you adjust it it'll increase or decrease the idle. Adjust so that your engine idles at about 1000-1200 rpm with ac on and in gear if it is an auto..this ensures that your compressor is spinning at the correct speed and that the extra load of the compressor doesn't cause your engine to lug when moving off..

[Cougar]

So now you know that there is about a 2 volt difference between your gauge and the actual voltage at the battery. The difference may get a little worse as more load is added but at least you are aware of it now.

 

Follow Kaz's good advice as the idle should be kicked up a little when the AC is turned on. It is the drop in the alternator RPM that causes the voltage to drop. Some alternators are able to charge better at lower RPM's, yours isn't one of them. There may be a bad diode inside it that is causing this. It may be good to have the alternator load tested at a shop to see how much power it can produce and check for a problem.