Where does this vacuum line go?

[hear]

I have the typical "HVAC stuck on defrost" situation. I've looked through some threads and I'm too stupid to understand what/where/how to actually perform vacuum tests. But in looking & poking around I did find this disconnected line which I don't know where it's supposed to go. Looks like it's blue, and it ties into the T fitting at the firewall near the heater core in/out pipes.

Where is this one supposed to go?

 

[WWII Jeeper]

I have the typical "HVAC stuck on defrost" situation. I've looked through some threads and I'm too stupid to understand what/where/how to actually perform vacuum tests. But in looking & poking around I did find this disconnected line which I don't know where it's supposed to go. Looks like it's blue, and it ties into the T fitting at the firewall near the heater core in/out pipes.

Where is this one supposed to go?

View attachment 363058

Maybe the vac canister inside the fender under the battery tray ? The lines seem a little short for that, but it's hard to tell from the pic.
Ray

 

[CharlesHS]

The smaller line may go to a fitting for a line going thru the fire wall behind the A/C accumulator drier.

 

[hear]

The smaller line may go to a fitting for a line going thru the fire wall behind the A/C accumulator drier.

The upper end definitely goes to the T that goes across the firewall & also through the firewall. It's the loose end that I can't find a home for.

 

[Mike Z]

Maybe the vac canister inside the fender under the battery tray ? The lines seem a little short for that, but it's hard to tell from the pic.
Ray

I had the same thought as you. The shape of the hard line and the curved rubber boot at the end sure do look like the vac line that goes to the canister in the passenger fender under the battery tray....but that being said, unless it is the angle of the pic, it does seem too short for that.

 

[hear]

I think I found where it’s supposed to go, but plugging it with a golf tee & also plugging it in didn’t change my defrost-only situation.

 

[Mike Z]

I think I found where it’s supposed to go, but plugging it with a golf tee & also plugging it in didn’t change my defrost-only situation.

View attachment 363062

That's the canister we were referencing. Any chance the rubber boot that plugs into the canister is cracked? It kind of looked like that in your first picture but was a little blurry.

 

[CharlesHS]

Maybe this vacuum line diagram will assist you in determining where the lines go.

 

[NskLJ]

The upper end definitely goes to the T that goes across the firewall & also through the firewall. It's the loose end that I can't find a home for.

If it is tied into the t then that end goes to the vacuum canister under the battery.

 

[hear]

That's the canister we were referencing. Any chance the rubber boot that plugs into the canister is cracked? It kind of looked like that in your first picture but was a little blurry.

It is cracked, but when I shoved a golf tee up in there it got well beyond the crack and didn't change anything with my HVAC, so it would seem that I at least also have a leak elsewhere.

View attachment 363084

Maybe this vacuum line diagram will assist you in determining where the lines go.

Man, I looked all over the FSM for that but I couldn't find it. What section did you find that in?

 

[CharlesHS]

It is cracked, but when I shoved a golf tee up in there it got well beyond the crack and didn't change anything with my HVAC, so it would seem that I at least also have a leak elsewhere.



Man, I looked all over the FSM for that but I couldn't find it. What section did you find that in?

The drawing is in the parts catalog.

 

[NskLJ]

It is cracked, but when I shoved a golf tee up in there it got well beyond the crack and didn't change anything with my HVAC, so it would seem that I at least also have a leak elsewhere.



Man, I looked all over the FSM for that but I couldn't find it. What section did you find that in?

There is vacuum testing in the fsm for 98 model very it should be the same as yours. Most of the time it is a crack in the supply line in the engine compartment. The vacuum line goes from the engine to the check valve then tees to the reservoir and inside. Check right where it goes into the firewall.

 

[hear]

Rather than continue to hijack somebody else's thread, I remembered that I had already started down this path on my own thread.

With a mightyvac and some small fittings I was able to determine that the black, yellow, and brown hold vacuum when I pump it from the HVAC control plug. The green, blue, and red don't hold vacuum.

I guess I need to re-test and see if I can actually get it to move to the floor, since I can hold vacuum on the supply line (black) and floor actuator vacuum (brown). But also given that I have vacuum on the supply line, it would seem that my issue is either the green/blue/red hoses are bad or the corresponding actuators are bad, or a fun combination of both. Looks like some of these actuators are halfway accessible so I can test and see if I'm on the right track. The PO bypassed the heater core (presumably because it was leaking) so I have a full disassembly in my future anyway.

I also don't understand how or even if the box under the battery comes into play with the hvac system, but the fact that the boot is cracked is probably not helping. The FSM doesn't mention it in the HVAC chapter

 

[NskLJ]

Will the actuators hold vacuum? If not, Check for disconnected hoses at the actuators. If the do hold vacuum check for a disconnected rod from actuator to the door. So you have vacuum at the supply line that is good and it held vacuum that tells you the check valve is good and the reservoir is not leaking. FYI the vacuum comes from the manifold then to a check valve then it tees off one line to the reservoir and the other to the supply line of the dash control. The check valve will hold vacuum in the hvac system when you go to wide open throttle and engine vacuum drops, the reservoir will keep vacuum to the system until engine vacuum returns. You are on the right track you can start the vehicle and use the vacuum pump to move the door to verify operation. Some modes may require more than one door to be supplied vacuum. In my experience the vacuum actuators are reliable, I would lean toward the rod being disconnected from the door. One more item is when you switch the dash mode switch it will leak vacuum between modes to bleed off the actuator that was applied then apply vacuum to the new actuators.

 

[hear]

Had 30 minutes to play before kid activities start.

I unseated & reseated the green line, and I can get it to hold vacuum, and I can hear the door open, and then close when I release it. I also discovered that if I pump the blue line up a little more, I can get it to hold pressure and I can hear the door open & close.

I fired her up and applied vacuum to brown & blue, but I couldn't get anything to happen. I also didn't feel any suction on the black line but I don't have a good way to test. I have a pressure gauge but the it's got like 1/8" fittings and everything I have looks like 1/4" fittings. Anyway, if I'm not feeling suction when I put my thumb over the hole, that probably means something in the engine bay isn't pulling vacuum, because I've already proven that line will hold it.

 

[NskLJ]

Had 30 minutes to play before kid activities start.

I unseated & reseated the green line, and I can get it to hold vacuum, and I can hear the door open, and then close when I release it. I also discovered that if I pump the blue line up a little more, I can get it to hold pressure and I can hear the door open & close.

I fired her up and applied vacuum to brown & blue, but I couldn't get anything to happen. I also didn't feel any suction on the black line but I don't have a good way to test. I have a pressure gauge but the it's got like 1/8" fittings and everything I have looks like 1/4" fittings. Anyway, if I'm not feeling suction when I put my thumb over the hole, that probably means something in the engine bay isn't pulling vacuum, because I've already proven that line will hold it.

Can you hook the mighty vac to the line to measure the vacuum?

 

[hear]

Can you hook the mighty vac to the line to measure the vacuum?

I did try that, but the needle didn’t move. I figured there was a reason that didn’t work.

 

[Wingback73]

Have you checked to make sure that the line on the driver side of the engine is actually connected to the engine? It is a loose fitting and is easy to knock off

 

[NskLJ]

I did try that, but the needle didn’t move. I figured there was a reason that didn’t work.

It should read vacuum sounds like no vacuum to that port. Connect it to another vacuum port on the engine to verify the gauge is working.

 

[hear]

It should read vacuum sounds like no vacuum to that port. Connect it to another vacuum port on the engine to verify the gauge is working.

I was able to connect the mightyvac to the gauge, was able to pull 30lbs, both gauges matched along the way = gauge confirmed to be working.

Have you checked to make sure that the line on the driver side of the engine is actually connected to the engine? It is a loose fitting and is easy to knock off

Just looked, everything appears to be connected, all the way over to the connection on the manifold.


The hose to the reservoir has a crack on the boot. I unplugged it from the reservoir and plugged it with a golf tee, but that doesn't seem to affect operation. I'm going to double check those tests here in a little bit. Is there a good replacement for this boot/hose, or do I just get some hose from the parts store and cobble together fittings to get the sizes right?