AC = massive power drain

[mondo77]

Hey all, well I live in Beautiful hot So Cal and it's starting to become AC time. Seeing as how i bought the truck in november I never really ran it till recently. As it turns out, it is a SERIOUS power drain on my little 3.0 with any AC on any level. a few other quirks are happening (explained in a bit).

First when I start from a dead stop (manual tranny) it takes considerably more gas, and clutch slippage than without AC. It feels like it is almost about to stall half the time, even with me finessing it. Is this normal?

My second gripe is that when I put the clutch in to change gears, the tach jumps up 250 or so, stays for about a second, and then starts to go down (no i'm not hitting the gas as i'm putting the clutch in). The only way to stop this from happening it if I release the gas, engine brake for half a second or so and then clutch it and it works fine. Why is that and is it normal?

And third, engine braking is pretty much non-existent with AC on. Why?

all help is greatly appreciated!

 

[Earl43P]

First: Sounds like your compressor is going bad or needs oil. It shouldn't make THAT much difference (mine doesn't). I pull out in 2nd gear a LOT and mostly feather the clutch at idle to get rolling, once the clutch is fully engaged, I gas and go (it's a pretty smoooth evolution - I've had riders comment that it feels like I drive an Automatic). Once in a great while I'll butcher that and get such a momentary low idle that the Oil Pressure Gage flickers to 0 and stall seems imminent.

Second: Normal. As long as you are rolling, it will do that. If you severed the VSS signal to the PCM (with a switch, say) it would not do that. Ford does that to help you match the rpms for a smoother shift (yeah, right) and help emissions.

Third: The PCM activates the IAC (Idle Air Control valve) with AC on for a slightly higher idle. Combined with the "normal" idle hang, it negates any engine braking by having that higher idle.

About the only thing I can think of is maybe you have a small vaccum leak. Check for any hissing noise at idle and inspect the PCV tubing for cracked elbow, split tubing, etc.

Mine will chug along at 18 mph in third gear, at "idle", never touching the gas pedal. High idle will get WORSE if you reset the PCM (by either clearing any CEL code or disconnecting the battery) and make it have to relearn its idle strategy.

I'd be interested to know your tire size and rear axle ratio.

 

[mondo77]

thanks for the info man! well I'm running stock tires, 235/75/15 on a final drive ratio of 4.10. Came stock that way with an open 8.8

and what exactly is the pcm? (noob, i know)

 

[85_Ranger4x4]

and what exactly is the pcm? (noob, i know)

Powertrain Control Module - it is the brain for your truck

 

[Earl43P]

So, you have the same gears and tires setup as I do, but 2wd = lighter.

You should not feel that much loss of power. I can drive back and forth to work several times and not notice that I have left it in the Defrost position (AC Compressor runs). I'll be sitting at a light and hear the clutch click and idle change, look down and note the switch position and flick it off. I won't say it's imperceptible, but I find it's easy to overlook that it is still on and cycling.

Either your truck isn't running well or your compressor is going bad. I can't tell which from here! Try cleaning the IAC (remove two 8mm bolts, spray inside it with carb cleaner, shake it dry, reuse the gasket, reinstall). See if that affects your idle/idle hang issues. Worth a shot.