Whistling noise from under dash

[Mathoran]

Been trying to track down this whistling noise for a while. Pretty sure its coming from the area behind the glovebox. Seems to happen every 10-13 seconds or so while at around 2k RPM. If I turn off the A/C the noise stops instantly. My only guess is something with the evaporator. Just had the blower motor out to check for any debris and because its also been making a ticking noise but everything was clean.

I made a video to record the sound. Does it 3x in the video with the last one (around 39 seconds) being the loudest. Doesn't seem that loud in the video but its pretty annoying. Any ideas?

Thanks.

 

[mrrsm]

Sounds like "Blower Motor Harmonics" are happening at a certain RPM-Frequency ... eBay carries an inexpensive replacement:

Heater Blower Motor fan ABS plastic For 2002-06 Chevrolet Trailblazer GMC Envoy | eBay

Find many great new & used options and get the best deals for Heater Blower Motor fan ABS plastic For 2002-06 Chevrolet Trailblazer GMC Envoy at the best online prices at eBay! Free shipping for many products!

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Also... A Long Time Ago.... @MAY03LT installed a Dual Filter set up inside of his Cabin Air Box. During the Follow Up... he showed just how much "Stuff" can get ingested into the Cabin Air Stream and perhaps some of THIS Junk is what is making that PITA Whistling Noise:

 

[Fishingguy]

Crazy, I just posted this same problem on trailvoy.com. https://www.trailvoy.com/threads/ringing-under-dash-only-when-a-c-is-on.212533/#post-1624794
Some of the helpful guys over there pointed me to this post.

I changed my blower fan and it did nothing.
I find it interesting that it only happens when the a/c is on and it has nothing to do with driving.

 

[mrrsm]

Most Blower Motor Fan Combos usually have Metal Balancing Weights made of Spring Steel positioned 'just right' along one or two of the Fan Impeller Blades. If these happen to move from their OEM factory positions... they might accidentally pick up energy from the moving air and vibrate like the Reeds in a Wind Instrument and amplify that tone.

The other possibilities involve the Bearings on either ends of the Motor Axle ends getting loose and likewise, picking up and amplifying the vibrational resonance when rotating at just the right cycle. The increasing amplitude will generally only occur at this point of Perfect Resonance.

The same can be said for any pieces of Plastic or Metal fitted nearby inside of the Air Box surrounding the Blower Motor that perhaps is just a little bit loose after so many years in service within the Air Stream are able to pick up that special resonance and drive you insane. You can't stress the difficulty enough in NOT being able to solve this issue.

Nikola Tesla created a small Resonance Device no bigger than the palm of his hand that he strapped to a Beam in the Basement of a New York City Skyscraper and he damned near managed to vibrate the building apart! For the same reason... Army Troops are NOT allowed to March In Cadence across any Bridge.

What is interesting here is that @Fishingguy 's Audio Clip from the TV Site is a DBOM (Dead Balls On Match) for the Sound and Frequency of @Mathoran 's Blower Motor.

 

[Fishingguy]

I'm changing the orifice tube next, hopefully it's the gas flow into the evaporator core that just happens to be at the perfect harmonic flow rate at 1800-2300 RPM. Good God I do not want to change the evap core.

 

[Mathoran]

I have a new blower fan on the way just in case and adapters so i can hook up my refrigerant gauges to see if pressures are within spec. I replaced the orifice tube, compressor and accumulator about 5 years ago, but I'm pretty sure the noise was there before. Seems like its gotten more frequent/louder though.

I took out my blower fan and stuck my phone in there to see the evaporator and everything was clean just some dust.

I was looking at videos on youtube about similar noises and found this comment for a honda.

"Your noise is caused by the evaporator outputting 100% dry (superheated) refrigerant into the suction line while the compressor is operating at low stroke, according to patent US6379121B1 column 8, allowing the suction reeds vibration to transmit to the evaporator as pressure pulsations. The fact that your sound comes and goes means that either the expansion valve or the compressor control valve aren't keeping the refrigerant flow stable for some reason. Running the AC at 38F ambient further compounds the problem because the compressor will be likely operating at a very low stroke and setting the internal temperature to 74F will mean that the evaporator will be warmer than the temperature at which the TXV de-superheats the refrigerant flow."

Don't think our A/C has all those parts but I don't know too much about it.

 

[mrrsm]

Nice Research... THAT also makes perfect sense to me...

For anyone else following along with a need to know... Right at the Aluminum Tube Junction along the Upper Passenger Side Fender Well adjacent the Radiator Coolant Reservoir, is the location of the HVAC Orifice Tube Aluminum Manifold. This is the place in ALL Automotive HVAC Systems where the High Temp, High Pressure Liquid Freon comes from the Compressor (through the Condenseor Coils) and is allowed to get metered and expand down the Short Line leading into the Firewall and thence into the Evaporator as a Gas,

This is called a "Phase Change" because the instantly expanding Liquid Freon literally "evaporates" and draws out the ambient Cabin Heat to make this happen. When you turn on the AC ...if you hear the A/C Compressor Mag-Clutch engage and THEN feel the exiting Vent Air getting Cold and then momentarily later hear the High Pitched Whistle... that would bear out @Mathoran 's Theory of the cause and origin of this problem.

The linked Video is excellent in describing the HVAC Under-Hood Layout. I've highlighted the attached screen print of the "HOT" High Pressure, Liquid Line Side in Red and the Cold, Vapor Return Lines and Accumulator side of the System in Blue. You'll need a pair of Needle Nose Pliers to pull out the Old, (Toilet Mung and Metal Laden) Orifice Tube and after lubing the New One around its "O" Ring Seal and Screen with a little PAG 46 Oil, re-insert it and VERY GENTLY tighten the Aluminum Manifold-Tube Fastener. Replace the Accumulator-Drier at the same time and follow the Book on pouring in the proper ounces of PAG 46 Oil, too:

 

[Mathoran]

Hooked up my gauges and if i hold the RPM around 2k when the compressor kicks in the low pressure drops from around 35 to about 0 pretty fast. The high pressure was going between 100 and 150 psi. So it just keeps cycling fairly quickly. Both seem very low so can I assume its just low on refrigerant? Ambient was about 80F. I haven't noticed any leaks but when the system was refilled it wasn't measured in or anything so it wouldn't surprise me if it was low since then.

It seems to blow fairly cold but vent temps are about 50F so could be colder.

 

[gmcman]

What are the temps at the vents when not using recirculation, and what is the ambient temp?

Also, what is the temp with the system on recirculate?

 

[Mathoran]

What are the temps at the vents when not using recirculation, and what is the ambient temp?

Also, what is the temp with the system on recirculate?

Just tested both Ambient was 73F for both. Recirculate was 50F, Non-Recirculate it went up to 60F at the vent.

 

[Mathoran]

Pulled vacuum and refilled with around 29 oz of 134 and some oil. Pressures seem good now. Vent temp got to a little over 50F but Ambient is 90F.

Wasn't able to duplicate the whistle noise in park while holding RPM at 2k now so it might be gone but I'm going to drive it around for a while before I call it a fix.

 

[Fishingguy]

Mathoran,
So you didn't change anything, only vacuumed and refilled?
Is the noise still gone?

 

[Mathoran]

Correct that was all I did and I haven't heard the noise since. Added some UV die and ordered a UV flashlight as well so I'll keep an eye out for leaks.

 

[mrrsm]

If you would enjoy avoiding the entanglements of having to introduce the UV Dye and then have to crawl around all over and then underneath the SUV to SEE whether or not it is effective while wearing UV Glasses... THIS Little Elitech-WJL-6000-Halogen-Detector can work in your favor... like Gang-Busters.

It will easily find even the smallest trace of R-134A leaking from your A/C Lines, Condenser Coils, Accumulator Connections and Low Pressure Sensor Screw In Seal as well as any Evaporator Leaks (Air Vents) that would otherwise require breaking into the Dashboard to locate with UV Dye on a Wild Goose Chase:

The only thing to avoid with this Amazing Device though, is making the mistake of trying to Test the New Unit by exposing it right out of the box to R-134A in direct spray concentrations. If you you do that... it will instantaneously Burn Out the Highly Sensitive Freon Sensor (A Replaceable Plug-In Unit that resembles a Three-Prong Transistor). Not too Bad for being available on Amazon for just Under $30.00:

Amazon.com: Elitech WJL-6000 Freon Leak Detector Halogen Leak Detector Refrigerant Gas HVAC R22 R410A R134A R1234YF CFCs HCFCs HFCs Detector High Accuracy: Automotive

Amazon.com: Elitech WJL-6000 Freon Leak Detector Halogen Leak Detector Refrigerant Gas HVAC R22 R410A R134A R1234YF CFCs HCFCs HFCs Detector High Accuracy: Automotive

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Read some of the Comments from the 2,750+ Fairly Satisfied Buyers...

 

[Mathoran]

If you would enjoy avoiding the entanglements of having to introduce the UV Dye and then have to crawl around all over and then underneath the SUV to SEE whether or not it is effective while wearing UV Glasses... THIS Little Elitech-WJL-6000-Halogen-Detector can work in your favor... like Gang-Busters. It will easily find even the smallest trace of R-134A leaking from your A/C LInes, Condenser Coils, Accumulator Connections and Low Pressure Sensor Screw In Seal as well as any Evaporator Leaks (Air Vents) that would otherwise require breaking into the Dashboard to locate with UV Dye on a Wild Goose Chase:

The only thing to avoid with this Amazing Device though, is making the mistake of trying to Test the New Unit by exposing it right out of the box to R-134A in direct spray concentrations. If you you do that... it will instantaneously Burn Out the Highly Sensitive Freon Sensor (A Replaceable Plug-In Unit that resembles a Three-Prong Transistor). Not too Bad for being available on Amazon for just Under $30.00:

Amazon.com: Elitech WJL-6000 Freon Leak Detector Halogen Leak Detector Refrigerant Gas HVAC R22 R410A R134A R1234YF CFCs HCFCs HFCs Detector High Accuracy: Automotive

Amazon.com: Elitech WJL-6000 Freon Leak Detector Halogen Leak Detector Refrigerant Gas HVAC R22 R410A R134A R1234YF CFCs HCFCs HFCs Detector High Accuracy: Automotive

www.amazon.com

Read some of the Comments from the 2,750+ Fairly Satisfied Buyers...

Ah thanks for reminding me. I actually have a similar one of those detectors that I had bought to use on a mini split.

 

[6716]

Not that this is your solution (or anything more than a coincidence) but I had that same issue and just replaced the evaporator and I do not have it now. If I had pressure in the a/c system, it made the noise. If not, no noise. But I wasn't holding pressure for long due to the evaporator. Now that it is replaced, no noise.

 

[Fishingguy]

Just replaced accumulator and orifice, added some oil, brought to a vacuum and recharged with new refrigerant. Noise seems gone. Thanks to Mathoran on the best advice on this issue. Will keep posted

 

[pell]

I have see here that replacing the evaporator is very time consuming and labor intensive job. Has any one tried going in from the engine side, cutting with air grinder or dremal tool?

 

[mrrsm]

You should never alter the structures of the Firewall. If I thought I could've gotten away with it, years ago I'd have bored out Two Wide Access Ports in the Firewall Hump of the Trailblazer to make it so much easier to R&R the Two Upper 4L60E Bell Housing Bolts. But even if I'd covered them up with Removeable Plates. it would have violated my Auto Insurance Policy... So... No Can (No Should) Do.