So it looks like the 2nd check valve is behind the HVAC controls. I removed the doghouse and it sits right above. See attached picture. Mines a 2001 with the 5.9 motor.

 

Widebody according to Moparfanatic21 in the 2nd generation Ram forum the new larger check solved his problem with the vents. He stated that changing the check valve with same one did not work. The fix is the larger check valve.k Thanks for posting the pic. My new check valve should be here sometime this week.

 

I ordered the new check valve in your link as well. It must have a small reservoir that holds vacuum as well. I couldn't remove the check valve shown in my picture. I sprayed some silicone spray and hopefully that loosens it up by the time the new check valve comes in. Hope this does the trick

 

Just got back from testing TSB fix for vents defaulting to defrost and the A/C worked perfect. Not one default in a two and half hour drive up hills and small mountains that required down shifting. No problems when accelerating to get on the freeway either. For me the twenty dollar fix worked well. The new check valve worked in my case.

 

thanks for the report. Did you replace the existing 2nd checkvalve or put the new larger checkvalve inline in the engine bay?

 

I replaced in the same spot the existing 2nd check valve was located. I had to remove the doghouse just like you. On our model of van you could not access it through the HVAC controls, you have to remove the doggy house. Mine was located in cluster of lines running to vacuum modulator that controls the vent airflow positions. You will need to pickup some hose fittings to adapt it. You might want to take to auto parts place and let them help you with the fitting of it. I hope it will solve your problem as it did mine. Good luck to you.

 

Think I'm gonna join you guys and install this same check valve too. I've read and seen the fix in 2nd gen trucks for a long time but never have gone ahead and done it...my 99 3500 5.9 has had the same vent switching problem (wild vents) for a long time, not a big deal and only occurs going uphill for a short time until let off the gas.
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I'm pretty positive it's not the under dash check valve as I had found that some time ago but it is some where in the vacuum line network or a failing connector or elbow... something simple but elusive. Will post when I get the part and test it out on mine too, also

 

Your correct J it's not really a performance issue but ....it was really nice not having that problem anymore. I wander why Dodge did not correct the problem themselves. The person I know that works in a Dodge parts department told me his 2009 Ram does the same thing. How many years does a problem have to exist before you include the fix in your trucks?

 

I just wanted to report that I ended up replacing the existing 2nd check valve behind the HVAC controls like the original poster did, and my wild vent is finally fixed. I highly encourage anyone with the same problem to do this simple fix.

thanks OP

 

Had the same problem, my check valve wasn't working at the intake. Just blew carb cleaner through it till it would check one way, works fine now, no vent change at low vac. I had installed cruise control on the van and thought that was the problem at first.