Engine/Transmission (1998.5 - 2002) Vacuum issues regarding vents

[Doug_Janowski]

2001 dodge ram 2500 cummins 5. 9l 24 valve 4x4 automatic with 217k.

The problem i have been noticing is my vents is stuck on defrost? I cant adjust the vents to your feet or your face or anything like that? My 4x4 still works and cruse control still works... . As far as i know both of these components are ran off of vacuum. Idk if i have a leak or my pump is going out? Anybody know how to help me?

 

[Ram4Sam]

Start at the connection at the vac pump and work toward the firewall, you will probably find a split hose. Mine was split at a tee fitting on the firewall. The hvac system defaults to defrost when there is no vacuum. Or the vac pump is kaput but I don't think that happens often.



Sam

 

[JLandry]

Doug,



If you're sure you have good vacuum, then a likely culprit could be the HVAC dash control unit to the right of the steering wheel. Besides being an electrical switch for the blower, this unit controls the flow of vacuum to select the HVAC mode. They occasionally fail and the result is defrost mode only.



Being several switches in one, unfortunately they aren't cheap... about $100 each from Mopar-Wholesale (a Dodge dealer in Florida selling Mopar parts online).



Dodge part number 5015734AA is WITHOUT heated mirrors.



Dodge part number 5015736AA is WITH heated mirros.



Before you consider swapping out that expensive switch though, I'd recommend you pull it from the dash and hook a vacuum gauge to the supply line to make sure the switch is receiving a strong vacuum.



Good luck,



John L.

 

[Doug_Janowski]

Now i have noticed that my vents would work some times and now i have noticed that my 4x4 light wont come on and cruse control barely works... so im thinking its the vacuum pump! I just bought a vacuum gauge and what is a good number?

 

[jwinnie]

Now i have noticed that my vents would work some times and now i have noticed that my 4x4 light wont come on and cruse control barely works... so im thinking its the vacuum pump! I just bought a vacuum gauge and what is a good number?

These vacuum pumps are strong. It should pretty much max out the gauge.

After I fixed my vacuum leak (cracked line to cruise servo) it was pulling almost 25in hg.

Check the vac right at the pump, then work your way out.

 

[Doug_Janowski]

Ok so i bought a gauge and i hooked it up straight to the pump and i was getting 28-29 in hg! So i guess thats a good thing? I guess now i will see if im getting good vacuum right at the firewall! and see if there are any breaks... .

 

[mwilson]

Doug,

See if you can borrow someones Mighty Vac hand pump. It is much easier to pin down the leaks with that rather than with a running engine.

Then you can test each heater function for leaks,etc. .



You can isolate leaks by taking the tees apart and blocking them one by one until you build some vacuum.



The gauge on the Mighty Vac will show up a leak very nicely. Start at the vacuum pump line and work your way back.



Mike.

 

[Fireman Dave]

Doug,



When this happened to me, I had a broken vac line going into the firewall on the passenger side. It was a hard plastic line near a Tee - as Sam said. It disappeared somewhere inside the firewall, so it wasn't all that noticeable at first. It was a real pain to find the other end behind the dash. I finally did find it behind the glove box. I could only work on it after the truck was cold since the heater core stayed hot for a long time.



Dave

 

[Ram4Sam]

Doug,



When this happened to me, I had a broken vac line going into the firewall on the passenger side. It was a hard plastic line near a Tee - as Sam said. It disappeared somewhere inside the firewall, so it wasn't all that noticeable at first. It was a real pain to find the other end behind the dash. I finally did find it behind the glove box. I could only work on it after the truck was cold since the heater core stayed hot for a long time.



Dave

That sounds just like what I need to do. My pass side windshield hasn't been defrosting very well, the airflow isn't near what the drivers side is..... I really hate working under the dash.....



Sam