280z mode door foam replace?

[chaseincats]

Quick question - the "mode door"'s foam I'm sure is on its way out because with the car on vent or AC, a small amt of heat comes through the heater vent on the bottom.  I tried pulling on the vacuum pod that opens/shuts it and it's all the way down.

Any idea how big (or small) a pain it is to re-foam the mode door (sometimes called the blend door)?  Is this doable without taking the dash out?

[Captain Obvious]

5 hours ago, chaseincats said:

Quick question - the "mode door"'s foam I'm sure is on its way out because with the car on vent or AC, a small amt of heat comes through the heater vent on the bottom.  I tried pulling on the vacuum pod that opens/shuts it and it's all the way down.

Any idea how big (or small) a pain it is to re-foam the mode door (sometimes called the blend door)?  Is this doable without taking the dash out?

First, to answer the question... No. It is not doable without taking the dash out. If you didn't have A/C, you miiiiight be able to replace the foam on the visible side of the door, but even so, that's not the side that you're having trouble with. You're looking to deal with the side you CAN'T see.

However...

When your system is switched to A/C, all coolant to the heater core supposed to be shut off.  Automatically. So if you're getting hot air out of the heat holes, the valve that is supposed to cut the hot coolant is leaking. 

If the air coming out is "ambient" (unheated and uncooled), then maybe it's just the foam on the mode door. But if it's hot, then you have more than one issue.

[chaseincats]

45 minutes ago, Captain Obvious said:

First, to answer the question... No. It is not doable without taking the dash out. If you didn't have A/C, you miiiiight be able to replace the foam on the visible side of the door, but even so, that's not the side that you're having trouble with. You're looking to deal with the side you CAN'T see.

However...

When your system is switched to A/C, all coolant to the heater core supposed to be shut off.  Automatically. So if you're getting hot air out of the heat holes, the valve that is supposed to cut the hot coolant is leaking. 

If the air coming out is "ambient" (unheated and uncooled), then maybe it's just the foam on the mode door. But if it's hot, then you have more than one issue.

Ah, I didn't think about that.  Yes, the small amount of air coming out of the heater vents is indeed heater hot.  I'm assuming replacing that valve is a messy and possibly dash-out repair?

Edited July 2, 2021 by chaseincats

[Captain Obvious]

I think if your hands are small and you are a limber gymnast (who have small hands anyway, so I guess the crack about the hands is redundant) I think you can replace that valve without pulling the dash. It's behind the blower motor tucked up where the heater core hoses are. It's a bundle of snakes down there.

However, first thing I would look into is... Is that valve getting it's signal to close? In other words, just because that valve is passing coolant even when it's not supposed to, is the problem actually in the valve, or is the problem somewhere else (like a dry rotted vacuum line under the dash)?

[chaseincats]

1 minute ago, Captain Obvious said:

I think if your hands are small and you are a limber gymnast (who have small hands anyway, so I guess the crack about the hands is redundant) I think you can replace that valve without pulling the dash. It's behind the blower motor tucked up where the heater core hoses are. It's a bundle of snakes down there.

However, first thing I would look into is... Is that valve getting it's signal to close? In other words, just because that valve is passing coolant even when it's not supposed to, is the problem actually in the valve, or is the problem somewhere else (like a dry rotted vacuum line under the dash)?

It definitely isn't the vacuum system since nothing changes when I pull the vacuum pod that controls the heater doors all the way shut.  When the heater is engaged that pod is what pulls the doors open.

[Captain Obvious]

Yeah, I took a look at the vacuum diagrams and it's not a vacuum leak. The no-vacuum "default" position of the water valve is closed and the default position of the mode door is "dash vents". In other words... If there is no vacuum applied to anything, you get recirculated air, unheated, out the dash vents. If you add evaporating refrigerant, you get cold recirc air out the dash.

So back to the original issue... It sounds like your water valve is passing water when it shouldn't be and your mode door isn't a perfect seal.

No you can't refoam the mode door in-situ, and working on that water valve up under the dash is "possible", but very uncomfortable without pulling the dash.

You could install a manual water valve up in the engine compartment. Being in Dallas, I gotta believe you could use a manual valve to completely cut off all the water to the heater core for most months of the year, and you wouldn't miss it. Wouldn't "fix" either issue, but it could be a relatively simple workaround for the majority of each year.

[chaseincats]

Gotcha.  You are a wealth of information per usual.  In this case I think I'll just stick with my warm feet lol

[Captain Obvious]

Glad to help. Sorry I didn't have better news or a simpler way to fix it.

And since I'm already the bringer of bad news...

The normal temperature control lever should also be able to block off the flow to the heater core. If you've got it slid all the way to COLD, then the heater core should be cut-off. Yes, when you switch to A/C, the other valve should do that automatically, but you should still be able to do it manually with the lever actuated valve.

So if you've already got the temperature lever slammed all the way to COLD and you're still getting a hot air through the heater core, then you've actually got three problems:

Your mode door foam is leaky.
Your vacuum-cokk valve is leaky.
Your temperature control valve is leaky.

All pretty much normal for these cars.