The stuck on derost problem

So i found the pill under the pass. side bumper. Is it the smaller vacuum tube that goes to the heater where i should be finding the leak or the big one that goes to the can? Also, what are the two little vacuum tubes that go to the air box? Im wondering because i want to make an intake possibly and need to know if those are important.
Thanks Guys

Its an 89' 4.0

Depending on what accessories you have there will be numerous vacuum lines.

Cruise, coolant control valve, D30 CAD axle and transfer case switch (NP/NV 231), and of course the HVAC motors.

The usual culprit is a busted hard-plastic vacuum line leading to the reservoir "pill" in the area adjacent to the battery.

Relocating the reservoir into the engine compartment, say under the pressure bottle on the firewall, will eliminate about 5' of problems, oops, meant to say crappy vacuum line.

EDIT: The small vacuum lines on the air box are for the thermactor system that takes heated air from the "stove" on the exhaust header and adds that heated air to the intake during warm ups. Pretty much useless, and is eliminated with cold air intake systems--just plug the little supply line.

joe_peters said:

EDIT: The small vacuum lines on the air box are for the thermactor system that takes heated air from the "stove" on the exhaust header and adds that heated air to the intake during warm ups. Pretty much useless, and is eliminated with cold air intake systems--just plug the little supply line.

Click to expand...

Mind you depending on your local regulations a warm air setup may not be legal and no one make a legal one for the Rennix models.

You can always run a vacuum line from the intake to the HVAC connection at the passenger side firewall to see if the problem is inside or under the hood.

MJR- EXCELLENT!!!!

Test there, then test near cruise/battery and takes it down to 1/3 of vac system in two moves, say less than 60 seconds! Neat! few feet of vac hose and fitting or two.

Well Done.