Why would the alternator click off and on every few seconds?

[toxcrusadr]

My '95 Ford Ranger (4L V6) has done this for awhile but it's getting more frequent. When it's sitting at idle, I hear a small click and the engine speed bumps up just a bit. Then it clicks off and the rpms go back down. Looking under the hood it appears to be the alternator switching on for a few seconds then back off.

Last week the battery got real low, it's a good battery (I think, couple years old) but it was very cold and I had moved the truck a couple times without driving it anywhere and I thought maybe it just got worn down. Maybe it's more than that. Anyway I charged it up overnight and it ran fine Saturday and Sunday. The red battery indicator came on a couple times in the first half hour while driving on the highway but that stopped. Drove it an hour or two with several stops Saturday and everything seemed fine, then again Sunday (no trouble lights at all).

But sitting still, that alternator was clicking on a lot more often and for shorter times, like 5 seconds each. Seems like the system thinks it needs to charge the battery but when it comes on, it changes its mind and shuts it back off. Seems like I ought to look into it.

Is it the alternator, the battery, or the charging control system?

 

[petehall347]

first check voltages at the battery and at the alternator output .
never heard of alternator behaving like that . with the clicking that is .
all i can think is worn brushes or sticking .or a bad connection somewhere .

 

[petehall347]

are you sure its the alternator clicking ? i would think its more like air con clicking on and off .

 

[gtxtom]

That sounds like A/C compressor operation. The clutch on the compressor kicks on when the system needs colder air. Run the car with the A/C off. If it is off, make sure it's not on defrost because on some cars, the A/C will run when on defrost even with the A/C switch turned off. Then see if it's still making the clicking noise.

BTW, they look pretty different. This is what the alternator should look like (roughly):

And the A/C compressor:

 

[MacNoob]

I came here to say that it's the airconditioning doing that, not the alternator. But everyone else beat me to it.

 

[SPL db]

Chris, if you had the defrost on while it was making the clicking noise, the above posts are correct.

Most systems will cycle the A/C on/off when the defrost is on. The theory behind it is that the cold evaporator coil de-humidifies the air and speeds the defrost.

 

[relaximus]

On our '03 Ranger 4.0L, the AC compressor also cycles when the airflow setting is set to vents/floor.

 

[toxcrusadr]

Dang it, you know I think you guys are right about it being the AC not the alternator. Depending on which engine you have they can switch places and I'll verify it later but it may be the AC. I'll have to see if it does it only when the defrost is on - I'm not at all sure of that. And the ON periods are so short, it seems like it would just wear out the clutch. Anyway I'll check it out when I'm home with the truck.

 

[toxcrusadr]

Relaximus posted at the same time. That's what I'm thinking, that it's doing it not just when the Defrost is on.

Personally I like a vehicle that lets me decide what I want on and off, but if the thing is doing what it's supposed to do and isn't broken, so be it. I'll check it out further.

 

[toxcrusadr]

Honestly I rarely turn that knob all the way over to Defrost, in winter it's normally on center/floor or defrost/floor. The latter probably turns on the AC too.

 

[SPL db]

On our '03 Ranger 4.0L, the AC compressor also cycles when the airflow setting is set to vents/floor.

View attachment 1101078

Looks to be the case...

SYSTEM AIRFLOW DESCRIPTION - MANUAL CLIMATE CONTROL

Max A/C
When MAX A/C is selected:

• The air inlet door vacuum control motor is at full vacuum, closing off outside air and admitting only recirculated air.
• The panel/defrost door vacuum control motor is at full vacuum and the panel/floor door vacuum control motor is at no vacuum position, directing airflow to the instrument panel A/C registers.
• The heater control valve (if equipped) is at full vacuum, preventing the flow of hot coolant to the heater core. Blended air temperature is not available.
• The A/C compressor will operate if the outside temperature is above approximately 6°C (43°F) .
• The blower motor is on.
• The auxiliary blower motor (if equipped) is enabled. Blended air temperature is not available.

A/C
When A/C is selected:

• The air inlet door vacuum control motor is at no vacuum, admitting only outside air into the passenger compartment.
• The panel/defrost door vacuum control motor is at full vacuum and the panel/floor door vacuum control motor is at no vacuum position, directing airflow to the instrument panel A/C registers.
• Blended air temperature is available.
• The A/C compressor will operate if the outside temperature is above approximately 6°C (43°F) .
• The blower motor is on.
• The auxiliary blower motor (if equipped) is enabled. Blended air temperature is available.

PANEL
When PANEL is selected:

• The air inlet door vacuum control motor is at no vacuum, admitting only outside air into the passenger compartment.
• The panel/defrost door vacuum control motor is at full vacuum and the panel/floor door vacuum control motor is at no vacuum, directing airflow to the instrument panel A/C registers.
• The temperature can be adjusted to heat the air but the air cannot be cooled below the outside temperature.
• The A/C compressor will not operate.
• The blower motor is on.
• The auxiliary blower motor (if equipped) is enabled. Blended air temperature is available but the air cannot be cooled below the interior vehicle temperature.

OFF
When OFF is selected:

• The air inlet door vacuum control motor is at full vacuum, closing off outside air from entering the passenger compartment.
• The panel/floor door vacuum control motor is at full vacuum and the panel/defrost door vacuum control motor is at full vacuum, closing off airflow to the defrost duct, side window demisters and instrument panel A/C registers.
• The A/C compressor will not operate.
• The blower motor is off.
• The auxiliary blower motor (if equipped) is disabled.
• The coolant control valve (if equipped) is at full vacuum, preventing the flow of warm coolant to the heater core.

PANEL/FLOOR
When PANEL/FLOOR is selected:

• The air inlet door vacuum control motor is at no vacuum, admitting only outside air into the passenger compartment.
• The panel/defrost door vacuum control motor is at full vacuum and the panel/floor door vacuum control motor is at partial vacuum, directing airflow to the instrument panel A/C registers and floor duct.
• Blended air temperature is available.
• The A/C compressor will operate if the outside temperature is above approximately 6°C (43°F) .
• The blower motor is on.
• The auxiliary blower motor (if equipped) is enabled. However, the air cannot be cooled unless the A/C is operating on the main climate control system.

FLOOR
When FLOOR is selected:

• The air inlet door vacuum control motor is at no vacuum, admitting only outside air into the passenger compartment.
• The panel/floor door vacuum control motor is at full vacuum and the panel/defrost door vacuum control motor is at no vacuum, directing airflow to the floor duct.
• The temperature can be adjusted to heat the air, but the air cannot be cooled below the outside temperature.
• The A/C compressor will not operate.
• The blower motor is on.
• The auxiliary blower motor (if equipped) is enabled. However, the air cannot be cooled.

FLOOR/DEFROST
When FLOOR/DEFROST is selected:

• The air inlet door vacuum control motor is at no vacuum, admitting only outside air into the passenger compartment.
• The panel/defrost door vacuum control motor is at no vacuum and the panel/floor door vacuum control motor is at partial vacuum, directing airflow to the defroster duct, side window demisters and floor duct.
• The temperature can be adjusted to heat or cool the air below the outside temperature.
• The A/C compressor will operate if the outside temperature is above approximately 6°C (43°F) .
• The blower motor is on.
• The auxiliary blower motor (if equipped) is enabled. However, the air cannot be cooled unless the A/C is operating on the main climate control system.

DEFROST
When DEFROST is selected:

• The air inlet door vacuum control motor is at no vacuum, admitting only outside air into the passenger compartment.
• The panel/defrost door and panel/floor door vacuum control motors are at no vacuum, directing airflow to the defroster duct and side window demisters.
• Blended air temperature is available.
• The A/C compressor will operate if the outside temperature is above approximately 6°C (43°F) .
• The blower motor is on.
• The auxiliary blower motor (if equipped) is enabled. However, the air cannot be cooled unless the A/C is operating on the main climate control system

 

[toxcrusadr]

Aha! It's all in the freaking manual isn't it.

 

[gadget73]

My Mark VII does that too, except it will kick the AC compressor on at any time the thing is in auto, no matter what the airflow setting is for. Bit of a goofy system but the idea is to reduce humidity in the cabin for better window clearing. It really doesn't wear the clutch out as much as you'd think provided the gap is right. Too big and it slips, then it goes bad quickly from that point; .

 

[quaddriver]

late to this party, but yeah, what they said. check for low freon if it just started doing this, the pressure cycling switch is either bad (it happens) or detecting low freon.

being a 95, it can go either way....r12 (cant do it) or R134 (easy as pie)

 

[leesonic]

Personally I like a vehicle that lets me decide what I want on and off, but if the thing is doing what it's supposed to do and isn't broken, so be it. I'll check it out further.

Good luck with that, the only way to get that is to buy an older car.

Lee.

 

[toxcrusadr]

^^ Yeah, I know. Although the Hondas had more flexible controls all along (owned 92, 02 and now a 2015). The 2015 Civic EX is highly electronic but still has separate controls for fresh air/recirc, temp, fan, and most importantly, AC on or off. Now it will still want to switch to fresh air and turn on the AC if you turn it to DEFROST but you can manually change those if you feel the need. What bugs me about the Ford is that the AC is turned on in three ventilation modes in addition to "AC" and "MAX AC" and you can't turn it off. And I've driven Tauruses and other models from the same era that were designed the same way. I guess I just like having manual override. Heck even the USS Enterprise had manual overrides and they used them a lot!

 

[toxcrusadr]

I will check on the AC Freon, that's a good point.

 

[Eric H]

You need to address the charge indicator coming on also, sounds like the Alternator is going out. If the voltage dips too low it may shut off the A/C, this could cause it to cycle too quickly at idle.

 

[petehall347]

you could always add a switch to air con clutch wire . it cant come on then if the switch is off .
best check battery and charging system first . might be a slipping belt . a burning hot pulley would confirm belt slip . mind your fingers on hot pulleys . dont ask how i found they can get super hot .

 

[relaximus]

Might also want to have the battery checked. Just because it's only ~2 years-old doesn't really mean much. It could have a cell on its way out.