I have a '98 f150 xlt with the 4.6. When I turn the AC on I experience a drastic loss of power. This only occures with the AC or Max AC engaged (compressor on). What could be causing this? How can I fix it?

I don't know if it's at all related, but my AC fan will only operate on high (the first three speeds are no longer functional). I assumed this was only a switch, a broken wire, or a resistor.

 

I heard someone say that an 18% power loss is experienced when you turn on the AC. This seems a little extreme, but it does certainly feel true when you are trying to get up.

 

Yes, you will experience power loss with the AC running. It takes a good chunk of power to turn the compressor. I don't know if it is 18% but I wouldn't say that is real far off either.

 

One of my cousins has a 2000 F150 with the 5.4 and was asking me about it a few weeks ago. Said when he turned on the AC, it felt like the truck was dragging. I thought about asking here, but forgot until I saw this post. Any other ideas on what it is?

 

Don't know about your power loss but you probably have a bad blower switch if you only have the high setting.

 

I've always experienced some power loss (when I got the truck it had 7 miles on it... it now has 120k) but this seems worse than ever. Could the compressor be freezing up, or something to that effect (on it's way out)? Has anyone else had what they viewed as excessive loss before? I know underdrive pullys are an option, but that's not the kind of money or effort I would want to expell to fix something that was never a problem before.

 

as of yet i have no power loss with the as on with a 5.4 ot olny has 2,000 on it

 

and i should say that is in a Screw to

 

The compresson rotor could be binding slightly due to worn bearing. You could check by taking the belt off and seeing if the rotor spins freely or not. If it is more loss then normal, and with those miles your the one that knows, then you could possible have a compressor that is going bad. I can't say for sure. It should spin freely when the clutch is not engaged, so you can try checking that or maybe have the dealer check it out for you.

It don't matter the size of the motor ALL motors will have power loss with the AC on, if it is working properly, more then with the fan and some people like to get the electric fans to free up power.

 

I don't notice a big change. I'd say less than 5%.

 

The resistor is probably the problem, high speed is the only speed that doesn't go thru the resistor. At least that has always been my experience.

Rob

 

I notice very little if any loss when I run the AC.

What I have seen in the past is when a blower motor only runs on high is when a temp sensor has gone bad and the system defaults to high to protect itself. Since you are loosing engine power I would guess the high pressure switch is bad. Did the loss of power and the high speed blower happen at the same time?

Your AC compressors runs on the other setting as well (Except floor) when the temp selector is all the way on cold. Try it on these other settings to see if you get the same power loss.

Good luck.

 

i notice a big loss of power too...its perfectly normal......just takes some power to turn that compressor......and i agree with the resistors being faulty......goodluck

 

Update:

Whatever was wrong has gotten worse. The engine is now misfireing on acceleration even if the AC isn't on. The check engine light came on yesterday. She's got a doctors appointment tomorrow, so I'll be dropping her off tonight. I'm only going to have them fix the engine and I'll play with the AC myself. I'll keep everyone posted on what the diagnosis is.

 

Seems she was playing hookie. The mechanic said she wouldn't do it for him. The code was for a spark plug i've been having trouble with for a year (hose leaked in it once, water got in it from driving thru puddles once...). He pulled the plug, cleaned it out, put it back in. When it was the plug before the idle was much rougher, it was a consistent miss, not like this time.

Could the problems be the coil? Does it go out all at once, or can it act up like this? How hard/ how much is it to change?

For now she's running fine again... I missed her, I think we'll go for a drive tonight, who's in?