Found during valve cover gasket install

[NC Tom]

Just want to know if I knocked something loose, or is this just another strange, unneeded part under the hood.

 

I noticed this canister, filter, alien tech while shoving hoses around trying to get the valve cover off. Don't see an open hose, so maybe it's nothing.

 

Thoughts?

 

 

[87MJTIM]

Looks like the heater control vacuum switch.

[Armyvet25]

exactly what it is

[Big_Mark]

20 minutes ago, Armyvet25 said:

exactly what it is

It's a vacuum driven "servo" that opens and closes the flow of hot coolant to the heater core when you move the heat/air/etc. control in the cab.

My money says nothing happens when he moves his lever 

[pizzaman09]

My factory plastic valve actually exploded when I was working under the hood and I got some darn hot coolant on me.  A new one was worth while, picked up at Advanced Auto in a day.

[NC Tom]

2 hours ago, Big_Mark said:

It's a vacuum driven "servo" that opens and closes the flow of hot coolant to the heater core when you move the heat/air/etc. control in the cab.

My money says nothing happens when he moves his lever 

Okay. Is there a diagram around that I can use to reconnect?

[cruiser54]

I'm not so sure that's the HCV. 

HCV is mounted further forward and higher. Follow the pinkish plastic vacuum line. 

[NC Tom]

1 hour ago, cruiser54 said:

I'm not so sure that's the HCV. 

HCV is mounted further forward and higher. Follow the pinkish plastic vacuum line. 

Will do!

[Armyvet25]

I'll take a picture of mine today for visual reference, if it is the HCV it normally has a lever that open/closes an inline fitting of your heater hose going into the core, and like he said, the pinkish vacuum line operates it when you adjust your cab selector from hot/cold.

[NC Tom]

16 minutes ago, Armyvet25 said:

I'll take a picture of mine today for visual reference, if it is the HCV it normally has a lever that open/closes an inline fitting of your heater hose going into the core, and like he said, the pinkish vacuum line operates it when you adjust your cab selector from hot/cold.

That would be great! Thanks!

[jpnjake]

This is the HCV I have in my chief, note it’s not running so not everything is hooked up, including the vacuum line. But without it connected to vacuum you shouldn’t have heat 

[Armyvet25]

[Armyvet25]

Here's a nice replacement

HCV replacement

 

 

[Big_Mark]

1 hour ago, Armyvet25 said:

Here's a nice replacement

HCV replacement

 

 

That's the widget right there!

If mine wasn't working I'd buy this one 

[Armyvet25]

1 minute ago, Big_Mark said:

That's the widget right there!

If mine wasn't working I'd buy this one 

for 10 bucks I'd buy one anyway and put it on a shelf

[gogmorgo]

If you do that it’ll last so long you’ll never remember where you put it. If it does fail just bypass it and order another if you really want, or just leave it bypassed. 

[NC Tom]

5 minutes ago, gogmorgo said:

If you do that it’ll last so long you’ll never remember where you put it. If it does fail just bypass it and order another if you really want, or just leave it bypassed. 

You are right. If I didn't install it then I would have no idea where I put it!

 

It's rainy here so I have not been out to check it. 

 

Just how many connections can be "bypassed" on an MJ? Seems like most of them. 😆

[Armyvet25]

42 minutes ago, gogmorgo said:

If you do that it’ll last so long you’ll never remember where you put it. If it does fail just bypass it and order another if you really want, or just leave it bypassed. 

mines rusty as heck, might still be working but I'm replacing anyway now that I'm acutely aware of it's condition

[AZJeff]

I am surprised anyone is really suggesting replacing that stupid thing.

 

The later XJ's eliminated this troublesome piece, and there were no adverse behaviors caused by that action.

 

I would just ditch the valve, and replace the heater hoses with the more modern routing that the later XJ's employed, and never look back.

[jpnjake]

15 hours ago, AZJeff said:

I am surprised anyone is really suggesting replacing that stupid thing.

 

The later XJ's eliminated this troublesome piece, and there were no adverse behaviors caused by that action.

 

I would just ditch the valve, and replace the heater hoses with the more modern routing that the later XJ's employed, and never look back.

I have this done on my Comanche, the only thing I’d say the valve is good for is my passenger complained about the heat from the dash without the heat on in the summer, the late xj’s don’t have that problem since the dash is thicker and insulates the passenger from the heater. 

[NC Tom]

Okay, is this the hose/line I am supposed to be looking for? I do get heat in the cab through the defroster. Honestly, I don't know if I get heat from the floor. Don't think I have ever checked. Not in a while anyway.

[pizzaman09]

If you have non terminated vacuum lines like that, you probably would only have heat on defrost anyway due to the vacuum leaks.  That sure looks like the correct line to me, should have a rubber 90 degree fitting on the end of the line.

[cruiser54]

Ditch the valve. Plug the tube. 

[NC Tom]

7 minutes ago, cruiser54 said:

Ditch the valve. Plug the tube. 

I'll do it!

[saveevryjp1998]

 

On 2/20/2023 at 5:28 PM, AZJeff said:

I am surprised anyone is really suggesting replacing that stupid thing.

 

The later XJ's eliminated this troublesome piece, and there were no adverse behaviors caused by that action.

 

I would just ditch the valve, and replace the heater hoses with the more modern routing that the later XJ's employed, and never look back.

It's there so hot coolant isn't running constantly through your heater core and to have proper working heat. That vacuum line opens the flow of coolant through to the core. Without it, no heat. With it constantly flowing bypassed with straight hoses, your heater core is hot in summer fighting your A.C. Pick your loss but it's there for a reason. They don't just put parts on because they don't have a function. Plug the tube, and you'll always have air trapped inside a chronic never ending closed coolant system. It works ya to get you home but it will catch up to you eventually. The bypass the bypass idea is just another bad idea which helps give the renix closed system a bad name. They fail because of dumb stuff like this on top of people not understanding the function. Think of it like you house plumbing. Block a vent on your crapper and see how well the turds continue to flow. I always fix that part, it's cheap, and easy. I also know my coolant system is properly working and my heat that way. It's also a good way to rot out a heater core leaving uncirculated coolant 24/7 year round to then eventually leak or rot out a passenger floor pan if you bypass core entirely. Guys do this multiple ways to save essentially a free junkyard part. Look for a metal one pre 90. They rarely go bad and are easy to test by simply opening the valve manually and plugging the tiny hole with your finger. If it holds open, the diaphragm is good and holds pressure. It's that simple. I'd fix the vacuum line, plug it on the bypass, and you're likely going to have full working heat as well as an actual defrost. It's common for the renix vacuum lines to dry rot and fall off the bypass. Once you fix the line, make sure you get up to operating temp, open the heater valve to high, and run it a bit. Chances are you'll need to purge the air in the system and refill some coolant if anything coolant wise in the system has been changed since the last time the heat was working properly.