(Searched) A/C Heater Vents Problem...

[miketodstjo]

This is my first post here, I've listened to alot of what you all have done for others, and it has always helped me out in my wrenching. I've got another problem with heater vents...

I have an 88 XJ Limited w/4.0 automatic.
Just replaced the water pump and hoses, thermostat and housing, steering pump and hoses, trans cooler and hoses, A/C condenser and reciever/drier + expansion valve, boiled the radiator, and rebuilt my alternator.

My right front fender has been 'bumped' in before I bought the Jeep, I can access just a little of the Vacuum Canister on the outside end, but cant remove it.

My problem is that like others, my vents will go to Defrost while under even a slight load, and they never fully disengage from the defrost(there is always a little comming out the defrost on all vent settings).

However, it seems that with the gear selector in 'Park', no matter how high I rev the engine(2500-3000 rpm) the vent will stay in the selected direction (vent, bi-level, MAX Air etc.) My cruise doesn't work but my 4x4 goes into Full or Part time mode with no problem.

I've looked at the lines and measured vacuum in a number of spots. My lines all look real good and my vacuum readings are as follows...

1- off the intake =35-38 cmh2o
reving the engine produces a momentary loss of vacuum followed
by an advance to 45-50 cmh2o vacuum.

2- at the canister, SOURCE hose is same as at intake35-38, or 45-50 with
revving.
black small tubing going to firewall and on to selector is 25cm-29
cmh2o, and looses a little vacuum on reving.

3- Halfway up the little black tube going to the firewall, I get 25-29 and it
will loose alot of vacuum (almost back to 0) before rebounding
and going up to 30-35, before leveling out around 25-29.

I've tried hooking up a NEW vacuum line from the canister to the firewall/selector, and the symptoms persisted. I tried eliminating the canister and hooking up a direct line to the firewall/selector (just to see what those symptoms were like) and got the same set of symptoms.

I've also tried looking at and resecuring the connections on the back of the climate control selector. But I didn't find anything wrong.

I'm stuck! I think it might be that the canister is bad; but I don't see any cracks in the canister, and it holds some vacuum. (as seen by the hiss an measurements I get when I release one of the hoses from it).

Is there something that might be gained by going in to the dash to trouble shoot? Are there any easy/quick ways to diagnos this further, or go into the dash?

Y'all have helped me so much before, with these threads and searches. Winter is comming fast and I need this vehicle to make it to the Hospital where I work at. Any help will be much appreciated...mike

 

[old_man]

I didn't have time to read and decipher all the places you mentioned reading the vacuum, but the most likely two places to have vacuum problems are the hard line that goes down and under the battery on its way to the canister, and the canister itself.

 

[areser0321]

The canister up under the front bumper should actually hold a vacuum. Take the canister out. There are two lines going into it. Use a hand vacuum pump to pull a vacuum on the canister while using your finger to plug off the other port. Listen carefully for any air leaks It should not leak at all. I was able to plug up a crack in the canister on my 88 xj with some rtv sealant and some duct tape. It has held for over two years. I am pretty sure that you can get the canister from your jeep dealer, quadratec, or find a working one from a junk yard.

Good Luck

 

[miketodstjo]

Thanks! I'll try that! I've got to get the front bumper pulled out about 2" though. The previous owner had a fender bender in that very same area and pushed it in.(which further makes me feel that the canister may be at fault, even if a slight vacuum is present, and no apparent damage is seen.

 

[miketodstjo]

Anyone else have some advice?

 

[FourCJsOneXJ]

Re: (Searched) Air Vents Problem

Reviving an old thread, sorry!

My 1995 Cherokee Sport is stuck in bi-level air delivery whether the lever is positioned for panel only, floor only or bi-level.

It doesn't matter if vent, heat, max or normal a/c is selected and happens regardless of rpm or engine load.

I haven't investigated yet as I just discovered it today when it was 100+ outside and I wanted panel a/c air. Worked this past Winter but haven't had a need to adjust or play it until now.

As an aside, between then and now I replaced my cranKshaft position sensor/timing probe or whatever commonly used terminology is acceptable today and did some limited work during the sensor replacement from the top in the engine compartment on the driver’s side near the firewall above the sensor if that makes any difference.

Thanks for any assistance!

 

[BarFlyFisherman]

An old school trick to locate a vacuum leak.
Start engine and let it idle.
Remove vacuum lines one at a time and spray starter fluid into the line.
If the RPM's increase then you've found the leak.
The replace that section of line or fitting.
Be methodical. Do one line at a time.

 

[FourCJsOneXJ]

An old school trick to locate a vacuum leak.
Start engine and let it idle.
Remove vacuum lines one at a time and spray starter fluid into the line.
If the RPM's increase then you've found the leak.
The replace that section of line or fitting.
Be methodical. Do one line at a time.

Thank you!

I date back to this era and then some, let's just say I'm a bit over the speed limit of most State roadways ways that abse same on Federal Funding.

Personally, I prefer something a bit less flammable around engines cold or hot but to each his own!

An induced RPM decrease is as good as an increase in my book.

Much appreciated, looking for information more specific to areas and parts to scrutinize verses general vacuum leak related diagnostics.

Again, thank you very much for your response, input and insight!!!

Bob

:us:

 

[ParadiseXJ]

An old school trick to locate a vacuum leak.
Start engine and let it idle.
Remove vacuum lines one at a time and spray starter fluid into the line.
If the RPM's increase then you've found the leak.
The replace that section of line or fitting.
Be methodical. Do one line at a time.

This will work fine for a leak in the engine side of the vac system. It will not work so well for the HVAC system. There's only one line that has anything to do with the engine side AND the HVAC side...it's the SOURCE line coming from the intake manifold...and associated check valve.

None of the HVAC side vac lines will affect the running of the engine.

 

[FourCJsOneXJ]

This will work fine for a leak in the engine side of the vac system. It will not work so well for the HVAC system. There's only one line that has anything to do with the engine side AND the HVAC side...it's the SOURCE line coming from the intake manifold...and associated check valve.

None of the HVAC side vac lines will affect the running of the engine.

Thank you! That source line just happens to be right in the path of where I was working to slip the new sensor back in place from the top on my 4.0L manual tranny rig.

I'll bet I cracked it bumping into it. Since it's attached directly to a relatively large diameter nipple on the rear intake runner any manner of spray testing that line should cause an RPM increase or decrease, I prefer a fine mist of H2O for safety sake which works 99% of the time.

I should have thought of that line but wasn't concerned with what it fed at the time and hence never considered it when this HVAC issue arose. You likely saved me a bunch of unnecessary digging around, much appreciated!
:cheers:

 

[FourCJsOneXJ]

Re: (SOLVED) A/C Heater Vents Problem...

Thank you! That source line just happens to be right in the path of where I was working.

Right place, wrong location!

That rear most vacuum port supplies all the “climate control” stuff plus several other key systems.

Walking it back to all the different “under hood” places it branches to visually, engine off and no spraying . . . I found the “culprit”.

It was a cracked small diameter hard plastic vacuum line that sits over the aluminum block on the passenger side at the fire wall which is fed by and has returns to the AC compressor/condenser and leads into the passenger compartment.

The plastic line had a small crack a half inch prior to where it enters a 90 degree rubber fitting which leads into the passenger area under the glove box. I’ve never touched that area or any lines in the vicinity.

It didn’t readily pull out of said fitting. I had planned on pulling it out, cutting back the cracked portion and reinserting it into said fitting as there was plenty of slack to do so.

Not wanting to force the issue and make things worse I just grabbed some black silicon oil resistant RTV gasket maker and slathered it over the wounded area of the line.

An hour later, problem solved . . . yippy!!! arty:


Many thanks to all . . . Bob