Intermittent AC Whistle or Whine

[Joe56]

In my 2014 Ram 3500 Laramie I have an intermittent whine whistle noise that is barely audible (wife says she can’t hear it) only when AC is on. It also occurs mostly or maybe only when I am in that sweet spot on the accelerator - when there is little load or little deceleration (like cruising) but in all gears when it makes the noise. It has been doing it for 16 months. 4 months ago, AC felt like it wasn’t working well and then sometimes it would work great. I did some checking behind the glove box and the recirculation door would hesitate and not close. I am in GA where it is hot 13 months out the year. I set both sides AC to 72 and leave it at AUTO. What I think I found is that the default setting for the recirculation damper is to open every time you shut off the engine and then it probably almost always closes when I start the engine to cool the truck. At that time, I helped the door close then unplugged the actuator, so it remains in always recirculate. Since then, I am back to great AC and heat when needed. If it was an older vehicle, I would swear I had a leaky vacuum line as they would fluctuate under different accelerations, but I think my Ram is all electrical in the heater box. I am fearful it is the compressor and will lock and leave me stranded ( I do carry an extra belt but not easy to change with that fan shroud). I have gone outside to listen under different RPMs but can’t hear anything wrong and I can’t seem to hear it inside the truck under different RPMs unless under load driving. Maybe a different blend door leaking but why at that 1500 to 1700 cruising RPM only? Thanks for any input.

 

[Topzide]

Do you park under any pine trees? I'm wondering if you might have some debris in the HVAC box. Have you added the cabin air filter option, or did your trim level come with it? Just trying to give you some ideas to check. If your air is cold, don't think it's the compressor, as this would be making noise that you would hear with the hood open. Vermin? When was the last time you had the software updated? With the auto HVAC system, there's a lot of things in play. Hope you can get it figured out. Keep us updated.

 

[Joe56]

Thank you! Stays garaged when not towing 5th wheel. I clean it meticulously and am under it every 6 months doing oil service and just inspecting it (I do all my own service) Not to say some small tree debris couldn’t have gotten in. No wire or rodent issues. No cabin air filter - did not come in the 2014 and have examined the area as I am thinking about it. I looked around the recirculation door behind glove box - saw no trash. I have received a software update for the radio when it froze after I tried per ram instructions with thumb drive while this was occurring ( I need to do a whole nother thread on that). They were able to do a forced update but still has issues with it being being black screen for a minute or two when first starting about every 4rth or 5th start. One thing I may have failed to mention is that if it is cold enough in the morning - below 70 - it will not do it (on auto set to 72) or if I click off auto and AC it stops. Fan speed does not make whine or whistle low or high with compressor off. I have even changed out the clutch fan (mopar parts from Genos) - idler pulley - fan pulley bearing and tensioner - water pump- all hoses during 100,000 mile maintenance. No change in that sound. Once I click AC on or Auto on and it is above the 72 set temp I can hear it whistle again when my accelerator is pushing that 1600 to 1850 sweet cruise spot. If it push the go pedal hard it stops OR if I let off completely it stops. I was thinking maybe it is the turbo but the sound is completely gone 100 percent if the AC is off and I can run heat or fan at any speed - no whistle no matter the rpm or cruise speed.

 

[petersonj]

I wouldn't rule out turbo whistle. Your description of the sound and when it occurs is exactly like turbo whistle.

The reason I would not rule it out is because when the AC lines get very cold where they enter the cab (as they normally do), different sounds could be transmitted from the engine compartment as the hose will get stiffer as it cools. There is a lot of liquid refrigerant in the line at that location as well when the AC is turned on...., and the turbo is located in that vicinity. The liquid refrigerant could transmit different sounds.

When you hear the "whine, whistle", does the pitch of the sound change if you let off the throttle slightly, or if you increase the throttle slightly?

- John

 

[Joe56]

Well yes maybe slightly- it is very quiet whistle - my wife nor sister can’t hear it and I am deaf in left ear from a brain tumor! The sound ONLY occurs in that cruising - non load - engine speed. Once I push on the gas or let it decelerate it goes away. But the instant I cut off AC it stops completely- no sign at all of the noise. I am religious about letting the engine idle and cool completely (10-15 mins if I even shut it off while traveling) before ever shutting off when towing or driving under load. I Change oil every six months since new - always between 4500 and 5500 miles and fleet guard lf 16035 and Vavoline premium blue 15 40. The turbo “should” not be failing.

 

[petersonj]

The turbo “should” not be failing.

Not suggesting that the turbo is failing, as it is quite normal for the turbo to produce a whistle.

Noises can sometimes be very difficult to diagnose, so I was just covering all possible bases. Another possibility..., a serpentine belt is under a heavier load when the AC compressor cycles on, so a worn belt could make a noise when the AC clutch engages. Some people have wired a LED lamp to the AC clutch temporarily to see if noises are associated with the AC clutch engagement. Just lay the LED lamp on top of the dash and monitor it while driving.

- John

 

[Joe56]

Thank you for your input. I put a new belt on with hoses and pulleys and a full egr service and found one of the clamps broken at the turbo on the air intake tube at that same time (8 months ago 99,000 miles). I thought this may be the source of sound source. Replaced all clamps from air filter to turbo. I also checked all turbo cooler boots. None loose or broken. Truck runs great but no change in whistle sound. And only when AC is on. If the radio is on moderately loud I never hear it - lol!

 

[Joe56]

Lamp may be my next and last resort!! If the noise is concurrent with the light - I guess I must assume I need a new AC compressor? At least before it breaks on me!

 

[Grumpy8811]

a man whose wife doesn't hear as well as he does is a rarity, bad ear or not. mine hears stuff I never even said..

anyway, its probably the engine cooling fan cycling, would be my guess.. as always, let it develop and if it is truly going to be a problem, since you already noticed it, you will figure it out if it gets worse.

 

[Joe56]

Wise words!!

 

[Topzide]

@Joe56, Get the cabin air filter kit from Genos. I added to my truck, shortly after I acquired it. Well worth the hassle, as it keeps all the trash out of the HVAC box. I cut mine with a Dremel tool with flex shaft. I like what @petersonj suggests with the LED. One of those tips you file in the ol brain box! Could be noises that are being transmitted into cabin as the truck ages. These trucks will drive us batty chasing down issues! good luck, and keep us posted.

 

[Tuesdak]

I am fearful it is the compressor and will lock and leave me stranded

I keep AAA, Good Sam, or other towing subscription on my older vehicles so I am not afraid to tow them Vs. pushing it breaking more $tuff. A compressor can break the drive tabs on the clutch and be a problem without ANY Warning.

When was the last time the A/C system was evac and recharged? Is this a OEM compressor? This is the only thing I would suggest esp. with the intermittent cooling you believe the recrc door (recirculation damper) fixed. These system slowly leak over time some faster than others.

It's possible another blend door has the sound when temperatures are just right.

I have several vehicles that whistle going down the road when in recurc from airflow. My 2018 RAM 3500 being one of them and it doesn't do it all the time. From a radio antenna, not likely, to a air leak at the windshield... The sound can be from many thing(s) influenced by the recurc door being in recurc.

As it's only with the compressor running... Interesting little fact that doesn't matter is the ideal RPM for a compressor is 2000 RPM for oiling etc. You may have found a harmonic or a flow rate where the orface tube makes noise. I would inspect the seals for the lines at the firewall as cold lines contract making more room for noise via airflow leaks there.

Last:
Compressor failure is noisy. Grinding, buzzing, hammering. If the compressor locks up the clutch slips and heat burns up a thermal fuse in the coil. As long as the idler bearing survives this you can continue. Sometimes it don't survive. Again with a whistle I wouldn't be worried about impending compressor failure. It's likely something else.