Bullnose Enthusiasts Forum

Bricknose Blend Door Issue?

Classic

List

Threaded

19 messages Options

Bruno2

Bricknose Blend Door Issue?

i have a 91 F150. I am having an issue with the blend door not operating. Also, there is a vacuum issue. When accelerating to get on the highway I lose air from the dash vents. It defaults to the defrost and eventually comes back. What operates the blend door when the switch is moved from hot to cold? I get the same temp no matter what position the switch is in.

Whitey: 1996 F 250 XL CCLB 4X4 7.3 DI ZF5 (The Work Horse) Lots of power mods
Whitey Jr: AKA Jr 1982 F 150 CCLB 4X4 351W C6 (Jr Work Horse) respectable power, but not over the top
The Bronco: 1987 Bronco XLT 351W C6 (needs work) Lots of off road mods and plenty of power mods
The Dodge: 2006 Ram 2500 CCSB 4X4 5.9 HO Cummins (The reliable ride that cant keep an AC in itself) (5th AC go around almost complete)

grumpin

Re: Bricknose Blend Door Issue?

Vacuum loss while accelerating is most likely a vacuum leak.

Dane
1986 F250HD SC XLT Lariat 4x4 460 C6-Sold
1992 Bronco XLT 4x4 351W E4OD
1998 GMC Sierra SLE K1500 350 4L60E
Arizona

ArdWrknTrk

Re: Bricknose Blend Door Issue?

Administrator

In reply to this post by Bruno2

Look at the vacuum motor beneath the passenger hood hinge.
Follow the brittle plastic hose into the harness bundle beneath the heater hoses connection.
This often cracks, and my solution is to splice it with rubber vacuum hose or small engine fuel line (that yellow/green Tygon you'd use for a chainsaw or blower)

The climate control vacuum starts from a port at the back of the intake, goes to a splitter (manifold) on the firewall/cowl, then there should be a line with a one way check valve.
Depending on your engine it likely goes to a vacuum reservoir (a black tin can or plastic ball on the passenger inner fender)

The tin cans are notorious for leaking seams or rusting out on the bottom.
From there the line should pass into the cab with that same bundle I spoke about above, where it comes out to the fresh air/recirc door in the plenum behind the blower motor.

Hope this helps!

Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.

Gary Lewis

Re: Bricknose Blend Door Issue?

Administrator

All of the above. And if the check valve isn't there or isn't working then when you accelerate the HVAC system loses vacuum. But if the check valve is there the HVAC system, being sealed, keeps its vacuum and it doesn't change modes.

Gary, AKA "Gary fellow": Profile

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI

Bruno2

Re: Bricknose Blend Door Issue?

Thanks Jim.

Bruno2

Re: Bricknose Blend Door Issue?

Gary, the truck did not do this before we did the AC job on it. We also changed the evap coil. I am thinking something got broken (frail little spaghetti line) or possibly something wasn't reconnected. It warrants further investigation.

Gary Lewis

Re: Bricknose Blend Door Issue?

Administrator

Yes, that line is frail. So check it out.

Gary, AKA "Gary fellow": Profile

FuzzFace2

Re: Bricknose Blend Door Issue?

In reply to this post by grumpin

grumpin wrote

Vacuum loss while accelerating is most likely a vacuum leak.

Well not really.
There should be a check valve between the vacuum supply and the holding tank to keep this from happening.

My check valve is in place but is bad and at times I can hear the air flow change where it is going.
So just because the valve is in the line check to make sure it is working.

And yes that tin can can also rust out and cause a vacuum leak, been there done that also.
Dave ----

Dave G.
81 F100 flare side 300 six / AA OD / NP435 / 2.75 gear
http://cars.grantskingdom1.com/index.php/1980-Ford-F100?page=1
81 F100 style side 300 six/SROD parts truck -RIP
http://cars.grantskingdom1.com/index.php/1981-Ford-F100

85lebaront2

Re: Bricknose Blend Door Issue?

Administrator

In reply to this post by Bruno2

Blend door is a purely mechanical cable system, open and remove the glove box door and look at the top side of the casing just to the left of the heater core access door. There is a lever or cam and lever that works the blend door. On the vacuum issue, use a small vacuum pump and go to the splice between the controls and HVAC system, apply vacuum to each port until you find the leak.

Black is vacuum source and white is fresh air recirculate actuator, both of these run out with the wiring harness through the top of the outer portion of the evaporator casing. If there is a vacuum reservoir on the inner side of the evaporator casing then there will be a tee in the black line.

This is from a 1990 EVTM but should be the same:

Bill AKA "LOBO" Profile

"Getting old is inevitable, growing up is optional" Darth Vader 1986 F350 460 converted to MAF/SEFI, E4OD 12X3 1/2 rear brakes, traction loc 3:55 gear, 160 amp 3G alternator Wife's 2011 Flex Limited Daily Driver 2009 Flex Limited with factory tow package Project car 1986 Chrysler LeBaron convertible 2.2L Turbo II, modified A413

myrl883

Re: Bricknose Blend Door Issue?

The temperature blend door is cable operated on these trucks. Vacuum operates the mode and recirculation doors only. It sounds like you have two separate problems.

Loss of vacuum will send all of the air to the defroster. This is a safety feature in case of malfunction - you'll still be able to see where you're going...

The plastic lines get more brittle with age, and the white tube to the recirc door is especially prone to disintegrating with age. They will usually just crumble if you pinch them. Replace/repair as necessary with small diameter rubber hose as recommended earlier.

Ford Parts Monkey since 1985
1981 F100 Flareside - Black, 302-4V Roller/AOD
1986 F150 Flareside - Medium Fire Red 302/AOD
1989 F150 Standard Cab 4x4 - Dk Shadow Blue 302/AOD
1993 F350 4x4 Crew Cab - 7.3 IDI/ZF-5
I think it's a sickness...

Bruno2

Re: Bricknose Blend Door Issue?

Update:

The cable and actuator is moving fine. I suppose it's the blend door itself. What does it take to get to it?

The vacuum problem was the fresh air/recirc line broken again. That is fixed good enough to last for a few days. At least I know what the problem is with the vacuum.

Gary Lewis

Re: Bricknose Blend Door Issue?

Administrator

Well, that's a big improvement. I don't know about the blend door. Maybe Bill or someone else does?

Gary, AKA "Gary fellow": Profile

ArdWrknTrk

Re: Bricknose Blend Door Issue?

Administrator

This post was updated on .

Gary, the blend door is right behind the heater core.
You can see that from the pivot.

So, Brandon, you're thinking it just needs a new seal?

ETA: have a good look at the seal going through the firewall.
If you're losing all the air to under the hood it is going to seem hot.

My cable sheath has slipped in its little clip atop the flange of the box before, but you say you can see the door working, sooo.

Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.

Bruno2

Re: Bricknose Blend Door Issue?

Jim, I am not sure. I changed the evap core when I did the AC job. Now I have had a few of these apart over the years to wash them out. I dont tnink I damaged the door. I know the box is sealed. I put weather stipping around the seams an coiled some backer rod around the evap tubing. The only place air is escaping is where the rubber hose comes out to drain the box.

I tried to feel around the mechanism that operates the door, but couldnt feel a pin for a hinge to see if it's actually moving the full range of motion. I think it's moving some just not the full range. There is no vent temperature change from hot to cold. I have the heater core shut off so it won't blow hot regardless.

85lebaront2

Re: Bricknose Blend Door Issue?

Administrator

Brandon, If I remember correctly the inside assembly (heater core and ducts) have to come out to actually repair/replace the blend door.

Blend door in cold position:

Blend door in warm position:

These are from the firewall side of the inside assembly.

Bill AKA "LOBO" Profile

Bruno2

Re: Bricknose Blend Door Issue?

Bill, the only way I can imagine being able to view the operation of the door is to open the box from under the hood. Maybe I can see past the evap core or manipulate it to see what's going on?

85lebaront2

Re: Bricknose Blend Door Issue?

Administrator

Brandon, first, remove the glove box, on the 1987-91, I believe you open it, depress the stops and it swings all the way down and unhooks. With it out of the way you can see the top of the blend door and either a lever where the cable goes or a cam the cable operates that moves the lever on the blend door. If all this is intact then you will need to look inside.

I have found that if you vent the radiator, then reinstall the cap, you can remove the heater hoses and prop them in the area behind the right hood spring. After that, remove the cover from the inside assembly and take out the heater core. You can now see the blend door from the back side.

When the door closes the opening from the heater core you are in "cold", with it opened away from the heater core you are in "hot".

Bill AKA "LOBO" Profile

grumpin

Re: Bricknose Blend Door Issue?

In reply to this post by FuzzFace2

FuzzFace2 wrote

grumpin wrote

Vacuum loss while accelerating is most likely a vacuum leak.

Well not really.
There should be a check valve between the vacuum supply and the holding tank to keep this from happening.

My check valve is in place but is bad and at times I can hear the air flow change where it is going.
So just because the valve is in the line check to make sure it is working.

And yes that tin can can also rust out and cause a vacuum leak, been there done that also.
Dave ----

With a leak the vacuum tank can only do so much. I had a small leak on the recirculating door plumbing on my Bronco and it would show up on long climbs in the mountains.

Had a big leak on my truck, hose knocked off by a mechanic, and it would catch up and go to vent, but any acceleration and it would go back to defrost.

Dane
1986 F250HD SC XLT Lariat 4x4 460 C6-Sold
1992 Bronco XLT 4x4 351W E4OD
1998 GMC Sierra SLE K1500 350 4L60E
Arizona

FuzzFace2

Re: Bricknose Blend Door Issue?

grumpin wrote

FuzzFace2 wrote

grumpin wrote

Vacuum loss while accelerating is most likely a vacuum leak.

Well not really.
There should be a check valve between the vacuum supply and the holding tank to keep this from happening.

My check valve is in place but is bad and at times I can hear the air flow change where it is going.
So just because the valve is in the line check to make sure it is working.

And yes that tin can can also rust out and cause a vacuum leak, been there done that also.
Dave ----

With a leak the vacuum tank can only do so much. I had a small leak on the recirculating door plumbing on my Bronco and it would show up on long climbs in the mountains.

Had a big leak on my truck, hose knocked off by a mechanic, and it would catch up and go to vent, but any acceleration and it would go back to defrost.

I am pretty sure it is the check valve as it did not "check" when I tested it.
The only plastic line I have left is inside the truck and it was in pretty good shape.
I also know the tin can is not leaking as I "sealed" it.
Dave ----