excessive heat coming from firewall: help please

[Craig 85]

That white piece is available new from LMC #32-2489 for $5.95. The door you are showing is the blend door (not the hot/cold door) and it is attached to the vacuum pod that is between the firewall and the A/C box (in red boxes). That door is centered by a spring. The vacuum pod in red can be pulled by vacuum in both directions. Moving the door back and forth. You can't see the second nipple on the back side. Picture #2 shows the nipple on the back side. I have the metal one. The plastic style is for 89-91's, but can be used on older trucks.

3. If I move temp control slider to cold , the heater core becomes fully exposed. If I slide it HOT the door shuts and you can no longer see the heater core. Is this correct ? Seems opposite of what I have read in this thread.

This is correct if you are looking from the cab towards the firewall like in your second picture. My picture below would have the yellow box up against the firewall in the inside of the cab. Sorry my picture is confusing. The piece in back actually fit into the cover in the foreground.

I just installed my system back in my truck today. If you need to actually speak to someone, PM me and I'll give you my number.

You must be registered for see images attach

You must be registered for see images attach

 

[chengny]

1. The actuator arm on the blend door looks broken.

It is - broken. Classic Parts has them in stock for $4.49:


https://www.classicparts.com/1971-87-Diverter-Valve-Link-Connector-W-A_C/productinfo/68-248/

But, that flap you are looking at isn't the "blend door" that everyone has been discussing. That is actually called the diverter valve. The diverter valve is connected to the bi-level adjust valve by a rod (the one threaded at the end).

Here is the parts list with an accurate drawing:

You must be registered for see images attach

The blend door is really called the temperature valve and I don't think its even possible to see it from inside the cab.

 

[DoubleDingo]

Yes it should because it's going to move the blend door to the cold side in the air handler and block off the heat. At least that's the way it should work.

I think it's also been mentioned, if you don't want the heat in the cab, you can also bypass the heater core and just look your heater hoses on the engine/radiator so no hot coolant is running to the cab.

I have a 3/4 x 5/8 adapter in the glove box of each truck when it's cold. When it gets hot I bring it out, disconnect the hoses from the core, and slip them on the adapter. When we drove over to Yuma last Thursday, when we gassed up in Palm Springs it was already over 100*, by the time we got to Yuma it was 123*. It was 117* at 730pm in the shade on the patio of our friend's house. Not having heat coming in from the core sure helped.

 

[RecklessWOT]

Maybe disconnect your heater hoses from the water pump and intake and put a plug back where the hoses were. Then you're sure not to have hot coolant flowing to your core. My heater doesn't work and the hoses are disconnected.

I was gonna say basically this. Try bypassing your heater core, if the heat issue goes away then you know it was just radiating off the heater core. If you have all your hvac stuff disconnected anyway then you probably won't mind not having heat.

I can turn the blower motor off, but heat will still come off the core unless I slide the lever to cold whether it's blowing or not. Probably your issue, just because it's not hooked up to the dash controls does not mean hot coolant isn't flowing through your cab.

 

[colonel mustard]

That white piece is available new from LMC #32-2489 for $5.95. The door you are showing is the blend door (not the hot/cold door) and it is attached to the vacuum pod that is between the firewall and the A/C box (in red boxes). That door is centered by a spring. The vacuum pod in red can be pulled by vacuum in both directions. Moving the door back and forth. You can't see the second nipple on the back side. Picture #2 shows the nipple on the back side. I have the metal one. The plastic style is for 89-91's, but can be used on older trucks.

3. If I move temp control slider to cold , the heater core becomes fully exposed. If I slide it HOT the door shuts and you can no longer see the heater core. Is this correct ? Seems opposite of what I have read in this thread.

This is correct if you are looking from the cab towards the firewall like in your second picture. My picture below would have the yellow box up against the firewall in the inside of the cab. Sorry my picture is confusing. The piece in back actually fit into the cover in the foreground.

I just installed my system back in my truck today. If you need to actually speak to someone, PM me and I'll give you my number.

You must be registered for see images attach

You must be registered for see images attach

Thanks for helping out. So if the door in your yellow square is in the position where I can not see the heater core, there should be no heat getting to the cab....correct ?

I’ll pm you and get your number this weekend when i have real time to tear into this.


Sent from my iPhone using Tapatalk

 

[colonel mustard]

I have a 3/4 x 5/8 adapter in the glove box of each truck when it's cold. When it gets hot I bring it out, disconnect the hoses from the core, and slip them on the adapter. When we drove over to Yuma last Thursday, when we gassed up in Palm Springs it was already over 100*, by the time we got to Yuma it was 123*. It was 117* at 730pm in the shade on the patio of our friend's house. Not having heat coming in from the core sure helped.

I was thinking I might get a **** off valve and do something similar.


Sent from my iPhone using Tapatalk

 

[Rusty Nail]

**** OFF VALVE!

SOMETHING....SIMILAR!

 

[DoubleDingo]

If you get the adapter the coolant still circulates, not sure if a **** off valve will allow the coolant to flow when it's **** off.

 

[Rusty Nail]

 

[colonel mustard]

Update.

I got the blower motor working correctly. Replaced the resistor , and blower motor. Also rewired a couple bad wires. And correcting a bad ground on the new blower motor. Now things are starting to work correctly again.

I have a couple questions now that I have a basic understanding.

How do I access this to replace it ?

You must be registered for see images attach

It looks like the vacuum line basically fell apart in it ... I’m assuming it’s the mechanism that opens and closes that door

You must be registered for see images attach

Do I need to remove the whole dang assembly to access it ? Cause that’ll suck balls.


Sent from my iPhone using Tapatalk

 

[chengny]

Update.

I got the blower motor working correctly. Replaced the resistor , and blower motor. Also rewired a couple bad wires. And correcting a bad ground on the new blower motor. Now things are starting to work correctly again.

I have a couple questions now that I have a basic understanding.

How do I access this to replace it ?

It looks like the vacuum line basically fell apart in it ... I’m assuming it’s the mechanism that opens and closes that door


Not sure what is that you think needs replacing. And it looks like you already have access. Here is an example of one that is fully intact:

You must be registered for see images attach

Do I need to remove the whole dang assembly to access it ? Cause that’ll suck balls.

No need to remove anything except the broken link itself. Back the screw out with a 1/4" nut driver. Then squeeze the pin that secures the connector to the link out with a pair of pliers.

You must be registered for see images attach

Sent from my iPhone using Tapatalk

 

[colonel mustard]

I guess what I’m asking or saying is that the vaccine line I circled in red is just laying there. It appears it should be connected to a nipple that should be around that vicinity. My assumption is it regulates that door being opened and closed. I can’t find the nipple anywhere.

You must be registered for see images attach

Sent from my iPhone using Tapatalk

 

[75gmck25]

The silver vacuum motor is on the other side of the plenum, connected to that door. That vacuum motor is what pulls the door back and forth, if its still connected. You need to find the vacuum line that runs to it, check to see that it has vacuum in the right dash positions, and then reconnect it to verify the motor works and moves the door.

The end of the vacuum line where it connects to the vacuum motor should have a light colored rubber connector that has a tab sticking out with a hole in it. The tab slips over the motor connector first, then the line is connected, and the tab prevents the line from slipping off.

Its fairly easy to replace bad OEM vacuum line by splicing in a good section. Good parts stores should sell GM 1/8" hard vacuum line in the "Help!" parts section. I think Dorman 47417 1/8" is the part you need, but I would compare it to your existing hard line. FYI - The Dorman main description calls it "soft" vacuum tube, but the detailed description calls it "hard emissions tube" vacuum line.

You can use short sections of rubber vacuum hose to push onto the hard line and splice where its broken. Keep the rubber line away from moving parts like the heat cable, since it is less likely to bind against a smooth hard line. It also a lot easier to thread that hard line through under the dash and over to the controls.

Bruce

 

[chengny]

I guess what I’m asking or saying is that the vaccine line I circled in red is just laying there. It appears it should be connected to a nipple that should be around that vicinity. My assumption is it regulates that door being opened and closed. I can’t find the nipple anywhere.

Sent from my iPhone using Tapatalk

That vacuum line (that you circled in red) pulls the HEAT/AC actuator to the HEAT position. There is another line that pulls the same actuator into the A/C position. The actuator is mounted to the outside of the air handling case on the front side - between the case and firewall.

In 1986 and up applications both of the the nipples used to connect the vacuum lines to the actuator are outside of the case:

You must be registered for see images attach

But prior to 1986, while the A/C connection was made outside the case, the actuator's HEAT nipple was located inside the case wall:

You must be registered for see images attach

The vacuum line was routed to the HEAT nipple through a grommet on the top of the case (item 31 in the dwg below):

You must be registered for see images attach

Weird thing is, one of the images you posted shows the vacuum line intact and entering the grommet:

You must be registered for see images attach

Then in another image, the line is parted and moved off to the right - the hole in the grommet is visible and the line no longer passes through it:

You must be registered for see images attach

Anyway, in order to connect the HEAT actuating line to the actuator, the case will probably need to be split to make the connection. Or maybe consider getting a post 86 style actuator and just reroute the line around to the back of the case. Both nipples will be accessible.

 

[colonel mustard]

That vacuum line (that you circled in red) pulls the HEAT/AC actuator to the HEAT position. There is another line that pulls the same actuator into the A/C position. The actuator is mounted to the outside of the air handling case on the front side - between the case and firewall.

In 1986 and up applications both of the the nipples used to connect the vacuum lines to the actuator are outside of the case:

You must be registered for see images attach

But prior to 1986, while the A/C connection was made outside the case, the actuator's HEAT nipple was located inside the case wall:

You must be registered for see images attach

The vacuum line was routed to the HEAT nipple through a grommet on the top of the case (item 31 in the dwg below):

You must be registered for see images attach

Weird thing is, one of the images you posted shows the vacuum line intact and entering the grommet:

You must be registered for see images attach

Then in another image, the line is parted and moved off to the right - the hole in the grommet is visible and the line no longer passes through it:

You must be registered for see images attach

Anyway, in order to connect the HEAT actuating line to the actuator, the case will probably need to be split to make the connection. Or maybe consider getting a post 86 style actuator and just reroute the line around to the back of the case. Both nipples will be accessible.

dang man....this was awesome info !!!! and great pics too thanks !!! That damn vaccum line just popped right off when I touched it by accident....that's why one picture shows it connected and the other doesn't. that's why im trying to figure out how to put the vaccum line BACK on to the actuator with out splitting the case.. I literally just got this thing working and then BAM. I knocked that vacuum line apart. . I would hate to have to undo everything I have completed to get that line where it suppoed to go ya know?