Three weeks ago I replaced my battery and serpentine belt as general maintenance before heading out on a prolonged trip. The next day I started receiving 'check charging system' whenever I turned the a/c on and the truck is at idle. Power steering becomes very hard to turn and engine feels like it is going to quit. This is not a problem at highway speeds. Looking at the engine when the a/c is engaged, a slow down of the belt/pulley is obvious. The alternator has been removed and checked, battery checked good, and the belt is the right size/length. What could be causing this? Again it started behaving like this after a belt and battery change. There is no issue if the a/c is off...but living in Texas?

 

Are you sure you have clean connections at the battery and the connections are tight?

Have you tried putting a multimeter on the battery at idle with the A/C on to see what the system voltage is? If the 2005 has an electric cooling fan, does the fan run when the A/C compressor is engaged? If not, maybe the fan is stalled causing a very high current draw when the A/C system requests it.

-Rod

 

When you turn on the AC, you are drawing more horse power and that pulls the motor speed down. AT too low of an idle, the alternator can not charge the battery as fasts as the usage, so the red light comes on.. Also a idle, you are not pumping enough steering fluid to properly steer the truck. ...... summary is the motor is running too slow. I think there is something that is suppose to increase fuel flow a few percent when the AC is engaged so that the motor speed increases slightly to compensate for the extra HP load. Im sorry, I don't know what increases that fuel/ rpm. You could set the idle up 100 RPM for now to compensate for the problem.

 

Thank you for your replies. Yes the battery connections and system/battery voltage are good. As I see it, the motor at idle does not increase the idle speed when the a/c is turned on. Looking at the engine running while someone turns the air on...you can see the engine bog down, the rpm of the belt slows and if the a/c is not turned off, the check charging system light comes on. Turn the a/c off...everything is back to normal...again, at highway speeds there is no issue. The problem only happens at idle, like stopping for a red light/stop sign, starting the car for the first time in the morning, etc.

 

Thank you for your replies. Yes, the system voltage/battery voltage is good. The battery is good. The problem is only when the car is at idle...such as stopping at a red light, a stop sign, etc. At highway speeds, everything is fine. Looking at the idling engine as someone turns the a/c on, you can see the engine bog down. The belt doesn't turn as fast..and if you don't turn the air off, the check charging system light comes on. The engine does not increase engine idle to compensate for the a/c and I know of no way to manually increase it. This is the 4.0 flex engine.

 

If the idle is dropping that noticeably when the A/C is engaged, that could suggest that the Idle Air Control (IAC) servo is not working properly. The IAC should increase the idle speed when the A/C is engaged to maintain engine speed.

You could try turning the steering all to way to one lock or the other at idle and see if again the engine speed drops. If so, that's a pretty good indication that the IAC is not working properly. Don't hold the steering wheel at lock for more than a few seconds though, it can be hard on the pump.

Before replacing the IAC you might try removing it and making sure the passages between it and the throttle body are clean. You can also try cleaning the IAC valve with throttle body cleaner, then reinstalling.

-Rod

 

Was the belt replaced correctly following the pattern on the sticker? Is the tensioner working keeping the belt tight?

 

I was going to say clean/ replace the IAC( does an '05 have IAC or is it drive by wire like the crown vic in 2005?)... tensioner bad( belt too tight) or
A/C compressor issue at clutch/pulley shaft drawing down and idle doesn't have enough ummph to overcome it? how many miles are on the alternator and the AC compressor? are they original or after market?

 

That's a good point. My 2004 Mountaineer V8 was throttle by wire yet oddly my 2004 Aviator V8 throttle was cabled. There's a good chance the 2005 Explorer was throttle by wire.

-Rod

 

Yes, my year model is drive by wire. The fan belt tensioner seems to be working correctly, the belt is tight. I have found a rebuilt throttle body online for $171 with a warranty, but my searching the web has many stories of that being replaced and the problem still exists. Re-flashing the computer seems a little extreme as this is the only issue and it just started happening after a battery/belt change.

 

throttle body seems extreme to me....if all is fine with A/C off and a new belt.... seems to me the new not stretched out belt making things too tight and you have some sort of pulley drag that the idle can't overcome when the AC load jumps in....

My throttle body is 13 years old... still works fine
but I have had to replace everything with a pulley, now that I am at 100,000 miles

 

As improbable as it seems...I replaced the automatic belt tensioner and all is well.

 

I didn't think it was improbable.... glad its fixed...