Dreaded HVAC Hiss

Anything related to the factory RPO Crew Cab.

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Dreaded HVAC Hiss

Post by Sonoma GT »

Does anyone have a vacuum routing diagram for a 2001 Crew Cab that they could email to me? The faulty T-case vacuum switch got me. I have the new switch in hand, new HVAC control head on the way and some new vacuum hose bought. I have been doing some reading on what needs done to clean out the system and was wondering how to access the vacuum reservoir in the fender. Has anyone been lazy and just put another reservoir in the engine compartment? I know that I may need new actuators but they are not in stock here so I'll see how they are after I tear in to it. Any advise is welcome. This is not going to be fun.
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Post by Sonoma GT »

I ordered a new vacuum tank that will be in tomorow. After some time spent testing the actuators with a vacuum pump the only one that seems bad is the dash vent to floor vent one. Of course its the hardest one to get to. I'm going to replace the vacuum tank,replace all of the rubber vac lines that i can get to, install new t-case switch, clean plastic vac lines,replace the bad actuator,replace HVAC control and then hope for the best. I sure could use a vacuum schematic and instructions for replaceing the vacuum tank. I wonder what the trade in value is on this thing.
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Post by F9K9 »

Sonoma GT wrote:..........I wonder what the trade in value is on this thing.
It could be allot worse. You could be forum ignorant and paying a dealership for the repairs. Sounds like you are doing everything correctly and researching thoroughly. I was just lucky that I found this forum within a month of buying my CC. It only had 600 miles on it was an '02 model. List was 27K in '02 and I paid 17K for it in '04. I am guessing you paid allot less for one with higher mileage but, all rigs have problems. Think higher monthly payments compared to repair costs. Just my Image. :wink:
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Post by Sonoma GT »

I thougt the Helms factory manual would have instructions on the vac tank R&R and the vacuum routing diagram. I don't have a factory manual. I'll get by without but the more info I have the better I like it.
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Post by F9K9 »

The hardest part is to remove the brake pressure modulator. Then just remove a single vacuum line. It will look like part of the inner fender.

GM DATA wrote:Brake Pressure Modulator Valve (BPMV) Replacement
Removal Procedure
Caution

Refer to Brake Dust Caution in Cautions and Notices.
Caution

Refer to Brake Fluid Irritant Caution in Cautions and Notices.
Notice

Refer to Brake Fluid Effects on Paint and Electrical Components Notice in Cautions and Notices.

Important

Thoroughly wash all contaminants from around the EHCU. The area around the EHCU must be free from loose dirt to prevent contamination of disassembled ABS components.
1. Disconnect the two electrical harness connectors from the EBCM (2).

Important

Make sure that brake lines are tagged and kept in order for proper reassembly.
2. Disconnect the 5 brake lines from the BPMV (3).
3. Remove 2 bolts (4) securing the BPMV mounting bracket (5) to the BPMV (3).
4. Disconnect the 2 way ABS pump motor connector.
5. Remove the four T-25 TORX® screws (1) from the EBCM (2).

Important

Do not use a tool to pry the EBCM or the BPMV. Excessive force will damage the EBCM.
6. Remove the EBCM (2) from the BPMV (3). Removal may require a light amount of force.

Important

Do not reuse the EBCM mounting bolts. Always install new bolts.
7. Clean the EBCM (2) to BPMV (3) mounting surfaces with a clean cloth.

Installation Procedure

Important

Do not use RTV or any other type of sealant on the EBCM gasket or mating surfaces.
1. Install EBCM (2) onto BPMV (3).

Notice

Use the correct fastener in the correct location. Replacement fasteners must be the correct part number for that application. Fasteners requiring replacement or fasteners requiring the use of thread locking compound or sealant are identified in the service procedure. Do not use paints, lubricants, or corrosion inhibitors on fasteners or fastener joint surfaces unless specified. These coatings affect fastener torque and joint clamping force and may damage the fastener. Use the correct tightening sequence and specifications when installing fasteners in order to avoid damage to parts and systems.

Important

Do not reuse the old mounting bolts. Always install new bolts with the new BPMV.
2. Install the four EBCM bolts.
Tighten

Tighten the four bolts to 5 N·m (39 lb in) in an X-pattern.
3. Connect the 2 way ABS pump motor connector to the EBCM (2).
4. Install BPMV (3) to EHCU bracket (5).
5. Connect the two electrical harness connectors to the EBCM (2).

Important

The brake pipes are held in the proper place by a frame mounted plastic bracket. Make sure that the brake pipes stay in the correct place for proper reassembly.
6. Install the 5 brake pipes to the BPMV (3).
Tighten

Tighten the brake pipe fittings to 30 N·m (22 lb ft).
7. Bleed the brake system.
GM DATA wrote:Vacuum Tank Replacement
Removal Procedure

1. Remove the brake pressure modulator valve. Refer to Brake Pressure Modulator Valve (BPMV) Replacement in Antilock Brake System.
2. Disconnect the vacuum hose(s).
3. Using a flat-bladed tool, depress the retaining tabs in order to remove the vacuum tank.

Installation Procedure

1. Install the vacuum tank. Ensure that the retaining tabs lock into place.
2. Install the vacuum hose(s).
3. Install the brake pressure modulator valve. Refer to Brake Pressure Modulator Valve (BPMV) Replacement in Antilock Brake System.
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Post by JaVeRo »

I have done the vacuum lines from the front actuator to the transfer case and then to the vacuum source near the brake booster on two of my S10's. I can't help you with anything in the dash. You probably already know most or all of this but it may help someone else down the line.

The way I would suggest would be to remove the three lines together keeping the three port connector on the lines so you don't get them mixed up.

Remove the rubber three port connector from the transfer case switch.

Remove the vent line from the transfer case. It connects to the vent line from the rubber three port connector with a "Y" connector. You can see the vent line at the top of the pic.
Image


Remove all the zip ties that hold the three lines to the transmission and dipstick.

Pull everything up from the transmission dipstick area.

The single line going to the front actuator is inside a wire loom going across the top passenger side of the motor. I removed the battery and tray and then disconnected the vacuum line from the actuator. I cut the head off a wood screw and screwed half into the old vacuum line and the other half into the new line, taped it up and used the old line to pull the new line thru. My wife fed one end while I pulled the other end.

Use the old lines to get the length for the new lines and replace one at a time. I marked the new line I run thru the wire loom every foot before pulling it to keep track of the total length and then cut it after I got the old line out and measured.

Tape the three lines together and run them back down the same way they came out.

I also split the two vent lines, running the vent from the top back of the transfer case separate from the vent from the three port connector. I don't know if it actually accomplishes anything but can't hurt.

While I was at it, I ran a new vent line for the transmission.
Image
The open end of the transmission vent line is usually stuck down into the wiring on the driver side of the transmission and tends to get plugged with dirt. I believe this is a contributing factor in transmission fluid being forced into the transfer case.

The vent lines from the transfer case and transmission were both ran into the passenger side fender with a filter on the end of both lines. Hopefully this will prevent a possible fire if fluid starts coming out of either one.

James
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Post by F9K9 »

Image

Image

You have remove part of the ABS to get to it.

Image
Sonoma GT wrote:........................I was hoping for a R/R how-to on.
Here's to hope.Image

It's already been said that you will be our first to do this. Document and take lots of photos for a "write up". :wink:
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Post by Sonoma GT »

It might be a little late for the picture and documentation part because I did not even think of that when I started. Arter part of the day working on it I have not even touched the Vacuum tank yet. It took most of the day to replace all of the vacuum lines and the t-case switch and then go out to by a new front axle accuator. It was full of tranny fluid. That switch was leaking real bad.I still need to clean out all of the plastic vacuum lines inside the truck,replace a bad floor-dash vent accuator, replace the HVAC control and put in that vac tank.I dont have some of the parts to finish this yet.
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Post by F9K9 »

Never to late to start if, you have a digital camera. Start from where you are at with photos and write up. I use one all the time just to remember how things go back together. Someone from here are another forum will be right behind you with this repair. They can fill in the blanks. If, you are doing this solo and no one is available to assist you then the bleeding of the brakes will require help. Google "speedbleeders" and pick up some at your local parts place. It becomes a one man job. Brake fluid should be flushed and changed anyway.

Good luck, Bro!Image
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Post by Sonoma GT »

Latest update. Many more hours spent taking apart the interior vac lines to clean them out with Simple Green cleaner followed by compressed air.This is a clean vacuum system throughout, I believe. Every part was cleaned or replaced.The new vacuum tank is in. Turns out you don't need to remove the Brake Pressure Modulator. That may be GM's method but I used the Brute Force method. You need to remove all of the brackets for the Brake Pressure Modulator and then carefully "finesse" the bracket out to access the tank. It's a tight fit. I didn't need all of the skin on my hands anyway. The vacuum tank was full of Transmission fluid also. The last step will be to replace the HVAC accuators and HVAC control when they arrive. Next week I hope.
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Post by F9K9 »

Sounds about right. GM advised us that the fenders needed to come off to remove the ZR5 flares. There was just a few screws from the flares into the fenders to remove. You did take some photos?
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Post by Sonoma GT »

I have a new twist to this saga.Today I thought that I would check the fluid level in the transfer case. I thought it would be low from the fluid being sucked all through the vacuum system. I opened the fill hole on the T-case and a flood of transmission fluid came out. It put out about 1 1/2 quarts to get down to the right level.It seems that while the fluid was being sucked out of the transfer case it was sucking fluid out of the transmission through the vent tube I guess. After thinking about this my fluid would have been blue if it came only from the transfer case because I had Auto-Trak fluid in it. All seems fine and I topped of the tranny fluid. I need to change the transfer case fluid if this is fixed.
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Post by HenryJ »

Keep an eye in things. The t-case is vented so I suspect that your transmission output shaft seal is bad.

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Post by JaVeRo »

Go back and read the last half of my post above. The vacuum switch you replaced has nothing to do with transmission fluid (fluid directly from the transmission). The vacuum switch causes contamination from the fluid in the transfer case which is usually transmission fluid, just not directly from the transmission.

I think the problem causing the transfer case to be too full is caused by the transmission vent getting plugged causing enough pressure inside the transmission to force fluid into the transfer case.

The transmission does not have a rear seal (sorry Brule, I just hafta disagree with you on this one). The only seal is on the front of the transfer case. It is my understanding that on Jeeps the transfer case adapter should be dry with a seal on both the transmission and the transfer case. That is not the case with these chevys. The transmission in the picture is still sitting under the carport and I can take a better picture tomorrow showing the weep hole. I can also post a better picture of the front of the transfer case if the board will handle the size.

I have a long drawn out theory of how all this is happening but so far I haven't found anyone that agrees with me. I may be wrong about the whole thing. It wouldn't be the first time.

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Post by HenryJ »

JaVeRo wrote:The transmission does not have a rear seal (sorry Brule, I just hafta disagree with you on this one). The only seal is on the front of the transfer case.
You are right. I should have said the seal between the transfercase and transmission. Transfer case input shaft seal would have been a better description. This seals the output from the transmission to the transfercase.

I really doubt that a plugged transmission vent would be the cause as the dipstick is not a good seal and typically shows the first signs in a situation like that. My experience has been that the seal between the two is a more likely suspect.

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Post by Sonoma GT »

I understand that the t-case and transmission are separate units that do not share the same fluid. The only way it could happen is through bad seals between them or through the common vent hose. My truck had fluid all through the vacuum system so my thought was that this was all part of that. After HJ's post about the tranny seal it made much more sense to me that that is more likely what is wrong. I need to check this out a little more.
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Post by JaVeRo »

The transmission shown is from the '03 Blazer.

The '01 Crew Cab my wife drives on the mail route was bought new and now has 169k miles with the same transmission and transfer case, neither have ever been pulled.

At about 75000 miles during the middle of the summer It started losing transmission fluid into the transfer case. I kept draining the transfer case down and adding to the transmission fluid until I had time to work on it. After a lot of research (mostly here) I replaced the vacuum switch and changed the routing of the vent lines. After summer was over, the problem went away.

Before the next summer I added a transmission cooler and the problem never came back.

My theory, and it's just a pea brained theory, the transmission vent gets stopped up and the transmission starts building pressure. Maybe 1/2 a pound more than air pressure but enough to start filling the transfer case slowly. Some of the fluid gets into the transfer case vent and since it is connected to the vacuum switch vent, you wind up with fluid on top of the vacuum switch just waiting to get in.

The vacuum switch has a vacuum source (always vacuum). When you put it in 4wd the switch applies vacuum to the front actuator. When you take it out of 4wd the switch connects the front actuator line with the vent line to equalize the pressure and release the front axle. This would let transfer case fluid into the actuator line if the fluid is present. The next time you put it in 4wd the fluid is then sucked into the rest of the vacuum system.

I don't know that this is actually happening but it's not that hard to just run separate vent lines and there will never be a chance of contamination from the vent line.

On the '01 crew cab I tied the transfer case vent to the transmission vent and ran it to the right fender well. I am running the same fluid in them. The vent from the vacuum switch is still tied to the transmission dipstick. With hindsight, I plan on separating the TC vent and the Transmission vent next time I work on it.

On the '03 blazer I ran separate vent lines for all three. I put Dex VI in the new Phoenix Transmission (thanks Steve, I finally got it installed) and the transfer case has Dex III in it. Dex VI is apparently not compatible with the transfer case. It also has a new transmission cooler installed. Heat is a killer.


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Post by Sonoma GT »

I'm going to replace the seal and run separate vent lines for the t-case and transmission. That should cover all possibilities. The rest of my HVAC parts should be here tomorow and I hope to have this truck totally done by this weekend.
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Post by Sonoma GT »

The new transfer case input shaft seal is in. I also put in the new HVAC actuators and HVAC control. I have a quiet non hissing and properly functioning system. Tomorow I will run a seperate line for the vent on the transmission and transfer case.
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Post by F9K9 »

I admire your persistence. Thoughtful, well researched and equipped with a plan of action! I hope that I will have that trait when a crisis arises with mine.

A model for me to follow but, I will probably stray "big time" and regret it the follow morning. :wink:
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