Anyone know what it could be with the fan turned on and im idling at around 750 rpm and every 10- 20 seconds I'll hear a click from the engine and the rpms will dip super low and even out again? No check engine light. Only happens with fan/heater on. Simple fix or a/c compressor or....? Thx in advance for any help.

 

Welcome to the forum

You have Defrost selected, so AC compressor should kick on and off, this is used to DRY the air in the cab, preventing moisture from collecting on cold window surfaces.

In some models this happens in any heat mode, to keep air in the passenger area DRY

But the computer should kick up the idle when AC Compressor is activated, it uses IAC Valve for that

You don't mention the YEAR of your Ranger so thats as far as I can go

 

Thanks for the reply! Its a 2006 4.0 fx4. It has just recently started doing this in the last couple weeks. So what you're saying is it sounds like idle air control valve?

 

No, in 2006 its could be AC system is low on refrigerant.

The computer has no AC pressure sensor it just turns on the AC compressor when cab Controller tells it to.
But the AC system itself does have TWO pressure sensors, which turns compressor off if pressure is too low or too high

And if that happens then computer is setting the higher idle like it should, but compressor turns off unexpectedly so idle goes higher then computer tries to fix it by lower idle then compressor comes back on unexpectedly and idle drops then computer tries to raise it,......................................ect...... ...................

If system is low on refrigerant then when compressor comes on it sucks in refrigerant, compresses it then sends it to condenser(high pressure side), if there is not enough refrigerant on the low pressure side then low pressure switch will cut power to compressor to prevent it from running Dry(ruining it), but as the high pressure refrigerant passes thru the system it comes back into the low pressure side so more refrigerant is there and low pressure switch is "happy again" and compressor comes back on, until refrigerant is used up again.................

So first thing would be to get pressure in AC system checked.

If its OK then you can move on to IAC Valve or other causes

 

Thanks again for the reply. Had a mechanic take a quick look and he seems to think the pressure is too high and wants to replace the black cylinder part I think it's the suction accumulator? As well as the pressure switch connected to that. Not sure if that sounds right or not? He disconnected the switch so the whole a/c system is off at the moment. As were going in to winter I figured it wasn't a big deal to get fixed just yet. Any other thoughts?

 

After he unhooked pressure switch have the RPMs stabilizes or are you still getting the "surging"?

Is the mechanic an AC guy or shop mechanic?
AC guy should know from just a few pressure tests what parts are bad.
Yes, system would need to be drained, parts changed and then refilled for suggested fix


AC is used in the winter to make the Defrost work better, it DRYS the air before it blows onto the windshield so it can "suck" up the fog/moisture on the window better/faster

And in the winter where I live its WET, lots of rain, so when you get into the car/truck you bring in LOTS of moisture with you on your cloths

The AC drying the air inside keeps moisture levels down so no musty smells over the winter months

So AC is not just a summer thing


You ever had a cold glass of refreshment on a warm day?
And the glass gets WET on the outside, thats because the glass is colder than the the air touching it, so it cools the warmer air and the warmer air has to drop off its moisture as it cools down so you get a WET glass.
AC works the same in the winter, and the summer as well, thats the water that drips out under the vehicle, AC cools the air enough to get it to drop its moisture on the AC coils and it drips out of the vehicle

 

Yes everything stabilized after he unhooked it, and he's certified in a/c. Said the same thing about the defrost not working as well too, so I may do it sooner than later. Thx again, it's nice to get some help narrowing it down.

 

So the AC was the problem causing the surging, good to know

I was wondering on the later model Rangers if computer was monitoring the AC relay, it isn't, even though the relays ground comes through the computer

If he's an AC guy then follow his advice, eventually you have to trust someone that's had hands on your vehicle

 

Hey man, I’m brand new here as my wife just bought her first Ranger the other day. Her’s is doing the exact same thing. Runs and idles perfectly until you turn the defrost on. Then, every 5 seconds or so, the RPM’s surge and the compressor clicks and the free wheel on it spins.

it’s really annoying and I live where it rains also still every day of the year so, we’re gonna need that defrost.

long story short, did you ever get that issue figured out and if so, what did you do????

Thanks a lot in advance, this is driving me nuts trying to figure it out