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Odd Sound Coming from TXV or Evaporator


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dw8
Novice

Jul 22, 2015, 7:42 PM

Post #1 of 11 (2200 views)
Odd Sound Coming from TXV or Evaporator Sign In

1994 Dodge Caravan SE, 3.3L, 98,000

I'm getting an odd sound in the passenger compartment (which appears to originate from the center dash area) ONLY when the A/C is on and the car is accelerating.
The sound can not be heard in the engine compartment.
At idle the sound is NOT heard NOR does the sound occur with just heat or blower only on.
I'm getting between 42 and 52 out of the A/C depending on ambient.
This has been going on for some time.
Last time I put gauges on they meet specs.

Before I recover the Refigerant, Vacuum and Recharge, anyone have any ideas what is causing this and whether a recharge will solve the problem?


Double J
Veteran / Moderator
Double J profile image

Jul 22, 2015, 10:14 PM

Post #2 of 11 (2191 views)
Re: Odd Sound Coming from TXV or Evaporator Sign In

Get a copy of TSB 24-12-94

Sounds like the condition you describe.


Here is an excerpt.....

Symptom/ Condition:

Under certain conditions, the internal flow of R134a refrigerant may set up a resonance in some evaporator cores.
This resonance can emit from the dash area as a high -pitched whistle noise. The whistle noise usually lasts 3-5 seconds and starts shortly after the A/C Compressor clutch engages. The duration and intensity of the whistle noise may vary as well as be highly intermittent. The whistle noise is most likely to be experienced at ambient temperatures above 85 degrees F and engine speeds around 2000 rpm.

This bulletin involves installing a different type of expansion valve.

Part # 4677334 expansion Valve
Part # 4677045 Gasket -Ex Valve to Evaporator
Part # 3846834 Gasket -Ex Valve to Refrigerant line


Double J
Veteran / Moderator
Double J profile image

Jul 22, 2015, 10:27 PM

Post #3 of 11 (2188 views)
Re: Odd Sound Coming from TXV or Evaporator Sign In

Just saw your post in the other thread ....

This bulletin applies if yours has the Expansion Valve with part # 4677203
But as of 3/94 production date, they changed to the new part # 4766334
If yours has that then this doesn't apply....


dw8
Novice

Jul 23, 2015, 7:04 AM

Post #4 of 11 (2169 views)
Re: Odd Sound Coming from TXV or Evaporator Sign In

Thanks for Reply:

I do have part # 4677203 per the TSB.
Interesting that it worked fine for a number of years but last 3 or 4 is when the sound started.
I also have the same problem I replied to with the gentleman with the 2007 Grand Carava-- that is -- the AC cuts out from the center vents and is redirected to the defost vents when extra power needed (climbing a hill).
I've tested the check value (canister) -- mine attached to brake booster -- and holds 8 Hg of vacuum as chec k value designed.
Have NOT set up a test jig to try and check all door accurators, but all buttons appear to function as designed and direct air accordingly.

Question:
1) Think the two issues are related or independent?
2) Know whether Dodge built in some kind of AC cutout in the PCM when extra power needed and air redirection is just Normal?

Thanks
David


Tom Greenleaf
Ultimate Carjunky / Moderator
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Jul 23, 2015, 9:46 AM

Post #5 of 11 (2163 views)
Re: Odd Sound Coming from TXV or Evaporator Sign In

Quote ">>
I also have the same problem I replied to with the gentleman with the 2007 Grand Carava-- that is -- the AC cuts out from the center vents and is redirected to the defost vents when extra power needed (climbing a hill).<<"


NO! That's not for extra power it's from loss of vacuum somewhere maybe not where you tested. Engines under load have no vacuum to supply so it's stored in a ball or can with a check valve in line for hold items where they were when no vacuum exists like asking for full or more power. For that they might (or some will add) a cut out for compressor under WOT = wide open throttle situations for max power.


Just to clarify just that,


T



dw8
Novice

Jul 23, 2015, 10:44 AM

Post #6 of 11 (2150 views)
Re: Odd Sound Coming from TXV or Evaporator Sign In

Mr. Greenleaf: Thanks for staying with me on this.


Quote
Engines under load have no vacuum

Agree that at idle max vac, as load increases vac decreases.

From what I can see the brake booster is the can as check valve connects directly to it.
From check value vac supply runs throught firewall to whereever -- most probably the A/C heater control assembly.

Unless the A/C heater control assembly is leaking somehow, you would think that if a button is pushed
which should redirect the vacuum to whatever door actuator, then climbing a hill would not cause air to be redirected to defrost.
ONly other things I can think of are:
1) the door is Not closing off completely and the air is bypassing it and consequently getting a redirect to defrost..
But if this is the case air should be coming out of defrost at all times.
2) When climbing the vacuum is dropping so low, that this is causing the blend door to close or close partially which
would then cause the air to be redirected -- defrost in this case.

Since the check values tests OK -- put a hand vacuum pump on it at 8Hg for 10 minutes and no leak down -- any idea how to troubleshoot this?


Tom Greenleaf
Ultimate Carjunky / Moderator
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Jul 23, 2015, 11:56 AM

Post #7 of 11 (2146 views)
Re: Odd Sound Coming from TXV or Evaporator Sign In

In a hurry somewhat - sorry. Vacuum booster will be on its own for all safety reasons. Other vacuum controlled anything (includes many mode control actuators for heat, A/C vents or blend controls on some vehicles) uses the storage ball or can. Ball I think on this AND a check valve. You know it works if engine is off the next day or even 5 minutes it should change modes with ignition on and engine off at least once. If not it leaks somewhere. Most common is under hood plastic line looks like wire. At first it has to have a crack or maybe melted spot till you get nothing than it will only put air out defrost as the default mode when things fail.


Your reading of just 8Hg (inches of mercury) is low. Engines spike vacuum upon deceleration, idle should be around 18+/-. While driving along it will be all over the place with assorted loads and hold the max it got in that storage can/ball.


This being now 21 years old is more likely to use more vacuum things that very new. Any leaks to the source intake manifold actual pressure will lower your reading but also run like crap but it isn't bad enough.


This could also be what you are hearing! Listen for it. No telling what a split vacuum something might do for a sound? Age and all still more likely under the hood.


Hard to think a TSB this late just decided to show up now but could have.


Back to work for me. Go listen for a leak in a line going thru firewall. Wiggle test might really show you which one. It's ok if you find plastic line to razor cut and splice in windshield washer size common hose over the bad part. Wire cutters can pinch plastic vacuum line and seal it closed. Good luck. I think that's your noise,


T


T



dw8
Novice

Jul 23, 2015, 1:56 PM

Post #8 of 11 (2137 views)
Re: Odd Sound Coming from TXV or Evaporator Sign In


Quote
Other vacuum controlled anything (includes many mode control actuators for heat, A/C vents or blend controls on some vehicles) uses the storage ball or can. Ball I think on this AND a check valve.

Only check I've found in engine area is the one on the brake booster.
Will have to remove center console to see if another one on same line in passenger compartment.

FWIW There are two lines in the engine compartment.
The vac supply going from -- brake booster > check value > firewall > inside cab (assume to AC heat control assembly)
Line from cab > firewall > Heat Control Value (this value turns off the coolant running to the heater core).


Quote
You know it works if engine is off the next day or even 5 minutes it should change modes with ignition on and engine off at least once. If not it leaks somewhere.

Great TIP. Will check it out.


Quote
Your reading of just 8Hg (inches of mercury) is low.

8 Hg is per Shop. I just had a hand vac without going to the trouble to set up a constant vac at 8 Hg to test each system component - hence the test of just the check value at this point.


Quote
Hard to think a TSB this late just decided to show up now but could have.


My thoughts too, that's why I asked.

Thanks for all your input.

=========================

Now to pull dash whichis a #$%^@ on this vehicle.


Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Jul 23, 2015, 2:10 PM

Post #9 of 11 (2134 views)
Re: Odd Sound Coming from TXV or Evaporator Sign In

OK - if vacuum is regulated to only 8Hg than so be it. That item could leak too.


Why are you pulling dash? Yes it's a total pest on most everything but be sure you need to,


T



dw8
Novice

Jul 26, 2015, 10:13 AM

Post #10 of 11 (2091 views)
Re: Odd Sound Coming from TXV or Evaporator Sign In

FWIW:

Used my hand vacuum pump and tested vacuum lines.
Everything appears to be OK vacuum wise.
There is a water value that controls flow to the heater.
Interestingly, per shop - if I am reading manual correctly (don't know how to upload pics for a second opinion) - the water valuve is only shut off in "A/C recirculation" mode.
Also interestingly, is when climbing a hill in A/C recirculation mode, no air is diverted from other vents to defrost.

Still have noise and when / if find the solution will post.


Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Jul 26, 2015, 10:39 AM

Post #11 of 11 (2088 views)
Re: Odd Sound Coming from TXV or Evaporator Sign In

There's your clue! Look at that water valve and see if it's also actuated by vacuum. Truth is that is either to delay heater blower or adjust flow volume for heater temp setting but the choice of recirc vs fresh air is yet another diverter door quite possibly run by vacuum also - just don't know every vehicle's way without a hunt.


So if that put the mode door (panel, floor, defrost or mixes thereof) all set then the leak is to do with that.
This just smacks of a leak of vacuum not yet broken entirely plus the noise could explain both. Reading if true of 8Hg could have meant 18 Hg or be because of the leak and not enough while leaking. BTW - vacuum available while running will vary from zero to spikes up to maybe 22 or more when engine is braking vehicle as in down hill. Doesn't matter the storage ball idea covers all that normally.


This is somewhat common especially with plastic (but rubber too) failures anywhere the integrity of vacuum is compromised. Usually near something that moves or in the way of something that you might touch to do something else plus if touching something hot they can melt a total hole now partial.


Again those plastic lines look a lot like wire but end up with rubber ends or elbows as needed.


More: If this is at the control head inside, diaphragms inside or hoses involved it will be a pest to be sure, worse if control head itself is plain worn IMO. Had those apart and wonder why some last for crap.


You may find multiple vacuum connectors here and there of rubber and a way to fasten that's either loose or broken too.


I really hope you can create the noise and find it by listening. Try tricks like using a long snouted funnel, plain stretch of hose might do, Once found the fix should be clearer what it will take.


Oh - for pics try using a hosting site like photobucket or tinypics is another. Link to the pic or try if it will show directly via copy/paste or whatever your device's way is,


T







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