Bricknose Funny AC Issue

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Bricknose Funny AC Issue

Bruno2
My son's 91 has been having some strange AC issues. The damper door that switches from the heater core to the AC evaporator core had been non functioning with the thermostat switch. So I opened the black box up and manually switched it over. When I did that the door didnt shut completely, but was giving up 70 degree air which is better than nothing when it's 100. As far as I can tell the door is cable operated and not vacuum controlled. So today my son was late for work. He was driving 85 mph down the highway. While he was at that speed the AC magically began blowing ice cold. However, when he slowed back down it was back to the 70 ish degree air.

Now I am fairly AC savvy. I have done a lot of AC work on vehicles over the years and have pretty good success if you discount the finicky Chrysler/Fiat stuff. I do have a 12 2500 Laramie I retrofitted to 152A that will blow 39 degrees out of the vents when it's 98 degrees outside. With that being said I am not AC ignorant. I am not the Guru either, but this one has me stumped. I cant imagine what a significant difference engine rpm would make on an AC . Especially with the problem he is experiencing mainly relates to a mechanical cable and not something vacuum operated.

Any ideas?
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)
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Re: Bricknose Funny AC Issue

Gary Lewis
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So it went back to its warm ways when he slowed down.  Bummer.  

Does that fancy DVM have a thermocouple prob?  Can you put it close to the evaporator and see if it is getting cold?  And drive it to see when it gets cold?

And what about checking the pressures when you rev it up to whatever R's it was turning at 85?

Hopefully someone that can spell A/C will come along to help 'cause I am not at all au fait with these things.
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

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Re: Bricknose Funny AC Issue

grumpin
In reply to this post by Bruno2
My first thought is your condenser is dirty or clogged up with debris and with added air flow, it gets enough flow to get it to cool better.
Dane
1986 F250HD SC XLT Lariat 4x4 460 C6-Sold
1992 Bronco XLT 4x4 351W E4OD
1998 GMC Sierra SLE K1500 350 4L60E
Arizona
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Re: Bricknose Funny AC Issue

ArdWrknTrk
Administrator
In reply to this post by Bruno2
Maybe driving that fast forced enough wind in the cowl to hold the blend door shut?

I am NOT A/C savvy, but I'd want to check how cold the evaporator is with the truck standing still.

How dirty is his condenser Brandon?
Did you try misting a hose into the grille while someone else sat inside to see if it blew colder?

Edit: Dane and I are of a similar mind!   

 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.
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Re: Bricknose Funny AC Issue

mat in tn
let's be sure that there are no other parallel symptoms. does the vehicles operating temperature change with these driving changes also? sometimes the thermostatic fan clutch can be bad and not provide enough cooling for the condenser even though the engine may not be as sensitive. a vehicles system has to operate across a wide range of environmental differences. unlike nearly all other small appliance which will have mostly fixed settings. some will have txv design to adapt to some variations but that's limited also.
even still, there is a time curve for optimal output  
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Re: Bricknose Funny AC Issue

Bruno2
Temp stays constant. We just did the fan clutch a year ago because we were experiencing higher temps at idle with the AC on.

I need to insert the thermocouple probe into the drain in the black box to see what kind of temp we're getting.
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)
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Re: Bricknose Funny AC Issue

Bruno2
In reply to this post by Bruno2
I didn't have my thermocoupler for my meter. However. The.line right below the orifice tube is cold. So the coil has to be cold inside the box. The vent.is still blowing like 70° air. The issue still has to be airflow across the coil,
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)
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Re: Bricknose Funny AC Issue

Gary Lewis
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I agree.  Something is going on with the door in the box.  Have you pulled the blower motor?  You might be able to see something there.
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

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Re: Bricknose Funny AC Issue

ArdWrknTrk
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This post was updated on .
A phone endoscope or even a inspection mirror might help.

So, you think it's a possibility that driving *85 might force the door closed?
 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.
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Re: Bricknose Funny AC Issue

Gary Lewis
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I have an endoscope you can use, Brandon.
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

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Re: Bricknose Funny AC Issue

85lebaront2
Administrator
In reply to this post by Bruno2
Brandon, how about the accumulator tank, it should also be cold. If the line going in is cold, but the one coming out isn't, believe it or not, you are low on refrigerant.
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

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Re: Bricknose Funny AC Issue

mat in tn
I will second that. I was reading along and picked up on the statement that the pipe right below the orifice is cold. all that means is that there is a pressure drop at that point. the immediate drop in pressure allows the liquid to flash to vapor and draw heat from all it contacts until it is saturated, and that saturation point needs to be very close to the drier making the entire coil a heat sink to absorb heat from the contacting air. if it reaches saturation before that then the whole coil does NOT absorb meaningful amounts of heat allowing warm air to enter and leave the coil at nearly the same temp. we always felt the accumulator/drier along with watching the gauges as to know when the saturation point was getting close. here in the south you can normally just watch it condense with all of our humidity.
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Re: Bricknose Funny AC Issue

85lebaront2
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Here on Virginia's appendix and the cities around the mouth of Chesapeake Bay, the temperature and humidity have a contest to see which gets higher (temperature ends up winning).

Right now at 10:09 AM it is: Temp 90° F, Rh 68% Heat index 103° F
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

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Re: Bricknose Funny AC Issue

mat in tn
great conditions for charging ac systems. condensation puddle under the car is a beautiful sight