NatB

As a follow up to replacing the manifold to HVAC vacumm hose-

I seem to have better performance and gas mileage ?

The vacumm line I replaced was really bad ( broke in several places) - meaning the engine was sucking in air. Would replacing the vacumm line really improve performance and MPG- or is this the " I changed my oil and the car is faster" rationalization?

Once again though - many many thanks to Matt and this Forum!!! Love having my AC really work again

madmatt9471

Heck no I don't mind

Thanks,Matt

madmatt9471

That's funny Nate - I don't know if it is enough or that-

Thanks,Matt

c5BlackBeauty

Excellent write up. Thanks. This will go in my reference file.

Bill Curlee

A few more picture and stuff for this excellent post:

Heres a couple of picture of the vacuum line with the 90 Degree fitting on the back of the engine.. I extended the line to make it easier, You can see the splice and longer line:







COOL LABLED PIC:




If you have a cut line, ADVANCED Auto sells a Nylon vacuum line repait kit that you can use to re join the line or splice in some extra line to make it longer to reconnect it easier.

Heres the back of the intake manifold




Hope this helps!

BC

madmatt9471

NIIIIIIIIIIIIIIIIIIIIIICE! That is gonna help tons of owners who are plauged with this prob!

Thanks,Matt

Bill Curlee

GREAT POST!

Keep up the geat work!

bliehr

Is there another place to tap vacuum other then the back of the intake manifold.
I have a 97 and just can not get my hand back behind the intake and I really don't want to remove it just for a vacuum line.
Any suggestions will be appreciated.

Thanks in advance.

Bill Curlee

Well,,,, seeing that you now have a constant VACUUM leak,, you really should fix the manifold connection on the back of the manifold...

I didn't want to remove the manifold on my 98 when mine came off and I used a mirror, a flashlight and a long screwdriver and after about an H O U R I got it back on.

So,,,,,,,,, its possible but I would rather remove the manifold, lengthen the vacuum line and solve the issue permanently.

Splice:



Longer line:



Here is a stock fitting. See how short it is:







Are you SURE that the line is OFF of the fitting?? Sometimes the nylon line inside the wiring gets damaged.

BC

FRITZM

I have the same problem on 2000 vert. Warm passenger air, so-so driver air. This is just the info i needed. Great info, thanx.

scottsphoto2

Yes,that was one good wright-up!
I know this was from way back in 08, but I may call you,(that is if you still have the same cell #?) to see if you may be able to help me with a little diff problem with my a/c in my 97. I just had a brandnew a/c system installed in 02/2011.I mean everything under the hood was replaced, that had anything to do with the a/c system. >>>> But now,about a yr and a half later, I am getting cooler air out on the pass-side, and HOT air out of the driver-side? I don't think the air on the pass side is as cold as it should be, but it is so much colder than the driverside.(Cause I do mean the DS is pure HOT) What should I check,,before taking it to the local Vette-Man? (hope I can get this fixed by my self>> because the Wife is getting tired of me pouring money into this car!)Lol>> But I love this car!!!

scottsphoto2

Me again! Just thought I would let you know to look for a email from me following this post,so you will have my email and phone # also!
Thanks for all you do to help a poor man! Lol

madmatt9471

Got it and emailed back at you

Thanks,Matt

trbprca

Thanks for posting this info. Just picked up a 99 coupe about a week ago and noticed it was having the A/C issue. Looks like this write up is going to help many of us for years to come.

82CEFan

Thanks to all who posted to this thread. I dug into my system today and replaced the vacuum line from the intake (fortunately I had already done the Oil sender mod and added extra line which made reaching it a breeze) to the inside if the car. I now have the proper air flow from the correct vents when selected.

madmatt9471

I'm glad it is still helping people!

Thanks,Matt

DevilMan02

Thank you!

madmatt9471

Right on!

Thanks,Matt

wcvette

Every time a Corvette changes hands, these threads become "new" info to someone.
Thanks to everyone for posting DIY info regardless of year or model.
BTW: I have to use this info tomorrow on my 98.
Thanks again.

Michael Pass

[QUOthaTE=madmatt9471;1566291441]I had air coming out oll vents on the Ac or Heat.

It was suggested that it is the vacumm supply line coming from the back of the manifold that is the culprit - Because Battery Acid Leaks on it and it burns through.

Well this is what happened or perhaps just it was rubbing and rubbed through thus allowing "NO" vacumm to get to the HVAC Vacumm manifold. (It did not have any Acid residue on it at all).

This vacumm line is "HARD" plastic and not easy to locate WHY? because it is within the wire loom going down to the area behind the passenger front wheel that goes to the PCM.

To Begin:
I had to jack up the front end of the Vette and turn the wheel all the way to the left, so I could remove the panel to access the area by the PCM and Vacumm junction One Way Check Valve.

You "WILL" need to take all the 7mm nuts off the panel (The ones underneath too) AND the last one for the fender on the bottom furthest toward the rear of the Vette right next to the door! This is because you will need to pull a little on the fender panel there to help see and work on the vacumm junction.

Here is the culprit fully pulled out: I tested it by capping the end after I removed it from the back of the manifold, it held "NO" vacumm at all- I mean I could blow through it and inhale through the line even though it was capped off on one end!


Damaged area:


It is not hard to get your hand behind the manifold with the Valve cover/coil covers off , plus make sure you unclip the MAP sensor it makes it a little easier too get your hand on the vacumm line- I pulled the rubber end of the line off the fitting in the back (there are only two fittings on the back for vacumm) One for the Brake BOOSTER and one for the HVAC Unit


After it was all traced out and I found the end in the fender well - It ran into a oneway check valve: (Pic) The line on the bottom comes from the manifold and the other two - One goes to the canister right above and the other goes into the Vette's Cabin to the HVAC vacumm block.


With it pulled off:

The bottom goes to the manifold (vacumm supply) the one off the side goes to the Canister above and the one in the middle (top) goes into the cabin area.

Next I re-routed the new vacumm line to the unit using 3/16" fuel/vacumm line: Plugged it into the Manifold and routed it behind the battery down to the canister area-



All tucked in:

Remember to re-plug in the MAP sensor

Next I went to the fender area and tested "ALL" the lines off the One-Way Vacumm Check Valve (Using my mighty Vac): Tested to 20 PSI, the only one that did not hold was the direct line to the manifold:


I went ahead and replaced the small 90* vacumm line to the canister for a just in case since it was easy enough(You never know) :



Now After that was done I went into the Vette and removed the floor mat, the panel covering the BCM (Computer) and the upper kick panel - now make sure you pop the foot well light out of the upper panel so you can remove the whole thing and have a free open area to work (YEAH! Like there is a lot of room anyway - all twisted on my back crunched in that little area- Stinking crazy! )

Here is a shot of the line coming into the cabin area from the fender:
They are kinda hard to see but they are the two (One from the manifold and one from the check valve to the cabin) there in the back ground right above the PCM:


Now I tested the line from the fender to the cabin, here is a shot inside the Vette - The Black plastic line from the One-Way Check Valve couples into a "PURPLE" Line : As seen in pics
Black plastic supply line: Seen at finger point


Pulled down a little to see the coupler: Black into Purple


A few pics of all the pretty colored vacumm lines from the vacumm block: (And to think I was getting no vacumm to this bad boy )



Next I pulled the Black to Purple Couple apart for testing and capped it off: Held very good at 20 PSI of vacuum for a sustained period of time:


I also tested the vacumm block and it held too

I was glad the supply line was good because I did not want to punch a hole in the firewall to install a 3/16" vacumm line, So I was able to use the factory one.

Since it was good at this point I buttoned up the inside and put it all back together - even the floor mat - no really I did!

Now back outside to the fender area where I re-assembled the One-Way Check Valve: Here are a few pics installed




At this point you can put everything back to factory - the fender screw and the panel screws and snug them all down - Lower the Vette back on the ground and make sure nothing was left off and no extra parts!

AGAIN: Make sure you clipped the MAP sensor wire back in - because you needed to pull it off for easy access to the vacumm fitting on the back of the manifold - You did put it back on right!

Well now it is time for the test:

Fire up - Turn on AC - Try different Modes - ALL WORKS GREAT - It's a cold party in here

DAMN this is awesome I can actually feel it on my face (Well after all the dust blast hit me in the face)

Now for the test drive - got to take my daughter to the bowling alley -OKAY let's go ! (I'll just test it out Right?)

Dude! I used to have to put it on FULL blast because it would come out of all the vents and now I had it on the third bar and had to actually turn it down to the first on the way back!

It's fixed - SWEEEEEEEEEEEEEET!

I hope all can benefit by this and if anyone ever has any questions feel free to call me 661-406-7516 (Cell also listed in my sig )

Sorry if it is a long post - But I'm happy and now I can drive a 639 RWHP Vette freezing inside when it is 112* outside all the way to the sunset!

Thanks,Matt[/QUOTE]