Funny groan sound with AC on

[tmcalavy]

My 93 Ranger XLT with 3.0 and auto tranny has started making a funny low groaning sound sometimes when I have the AC on and the rpm's down under 1K...like at a stoplight or stop sign. Doesn't groan with the AC on Max, or with the AC off. Kinda sounds like a small airplane flying over in the distance. Disappears as soon as you get the rpm's above 800 or so. I had the compressor, dryer and evaporator changed out last summer along with a system evacuation and recharge. Anyone familiar with this?

 

[adsm08]

If the last compressor blew up and they just replaced parts but didn't flush it out properly, well that can blow up the new compressor.

Think about it like this: Your engine runs out of oil, spins a bearing, and blows up sending metal shavings through the whole system. You go out, get a brand new engine, put it in, and throw the old oil filter on the new engine.

It will run for a while, but then it will suffer the same fate as the first one. Same goes for your A/C system. A lot of shops just replace the compressor and drier and never flush the lines or replace the orifice tube, they shoot it back up and BAM, all those nasty little pieces of compressor that stuck to the sides of the lines in drops of oil start getting circulated around the system again.

 

[tmcalavy]

Yeah I understand the concept, but I don't think they did that...I did a lot of business with that shop while we were in W. Texas and they never funked anything up. Don't think it's the compressor cause I can stand in front of the engine with the hood open and the AC running and the sound will come and go...just like when driving.

 

[adsm08]

OK, so go stand in front of the truck until it starts making the noise, then unplug the compressor. See if it shuts up.

 

[Earl43P]

While you are at it, unplug the IAC too.
They have been known to hum.

 

[tmcalavy]

I found time to stand in front of the running engine with the AC on low this morning, after cleaning and rearranging the garage and fiddlin' with the riding mower deck a little. The hum/groan comes and goes with the AC cycling on and off, but I don't think it's the compressor or the IAC. I noticed while watching/listening the compressor that the sound is loudest right over the driver's headlight, so I think something down in there is vibrating...like a loose heat shield on an exhaust system. What is that small rectangular cannister right next to my battery? Is that the vapor cannister for the fuel tank? It has lines running to it and two, small removable caps on the the top of it...sits just to the left of the battery tray. What is underneath the battery tray, down between the bottom of the radiator and the driver's wheel well...anything that could rattle/vibrate? Anyway, now that I know it's not the compressor moaning I'm not that paranoid/concerned about it.

 

[PanamaExpat]

Yup that's the vapor canister. There is a solenoid in the breather line from the tank that opens to allow the engine vacuum to vent the fuel tank. Maybe the solenoid isn't opening all the way or something, is weak and vibrating, or something is restricting one of the lines or the canister is full of muck. Unless you have some rust issues I cant think of anything short of the canister mount itself that could vibrate in that area. If you have never removed it the battery box is bolted and welded so I doubt it could be that.

As for your AC compressor cycling.... Have the freon level checked. They tend to do that when the system is borderline low.

 

[Trfsrfr]

I have the exact same truck, and HAD a very similar groan/moan until a couple weeks ago when the A/C compressor went.
Now I dont have that noise anymore.
I always heard it at stops. I remember wondering if it was me or the car beside me.
And as you stated, once I got around 1000 rpm it went away.
I also thought it might be my steering gear at first.
I used a long 1/2" extension up to my ear and pressed it to the P/S bracket, which is also the A/C compressor bracket, to "listen" to the noise but couldn't determine if it was one or the other.
Now I know, it was the compressor.
Hopefully your problem is different
Also - my compressor cycled every 3 seconds.