Small vacuum line leak affecting a/c vent? - Ford Bronco Forum
 
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post #1 of 9 (permalink) Old 10-13-2010, 12:38 AM Thread Starter
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Small vacuum line leak affecting a/c vent?

When I get on the gas (e.g. going up hill), I lose air flow coming out of the vents (with or without a/c). I know these lines are vacuum operated but I can find or hear any leaks (including the white line). Is there any way to pinpoint this? Do I just need to look harder? Most of the time air flows just fine out of the vents, it's only temporarily lost while stepping on the gas.

Thanks,
BB
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post #2 of 9 (permalink) Old 10-13-2010, 01:10 AM
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Bronco Info: 1995 XLT 351W, 2.5 R/C Lift,4.10's, Rancho Extended R/As, 33's, Punisher Valve Body
Yeah, I would keep checking, by what you describe sounds like a vaccum problem. Check the piece(don't know the exact name of it)that the white vac line connects to.

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post #3 of 9 (permalink) Old 10-13-2010, 08:24 AM
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Bronco Info: 92 Factory Original 300 I6 M5OD Manual Custom. 3 seats, AC and a radio and all vinyl interior.
Yes, you have a leak somewhere. Sometimes, it's a crack so small that it only shows itself after the engine bay warms up enough to cause expansion. Look at your exterior lines and see if they are hard or brittle. If they are replace it. They should be easily flexible and pliable. You may even just see a powder on your hands if you touch them. If so replace it at least down to the softer flexible area. There's a link in my sig showing how I fixed mine. Maybe it'll help.

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MY A/C Vacuum leak repair http://www.fullsizebronco.com/forum/23-technical-write-ups/175808-how-i-fixed-my-c-vac-leak.html
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post #4 of 9 (permalink) Old 10-13-2010, 09:18 AM
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yo, here is da skinny;
"...In 92-96, The air handling system is designed to provide defrost when no vacuum is applied to any of the three air door vacuum motors. This is done to prevent a situation where defrost cannot be obtained due to a system vacuum leak. Instead, a leak in the vacuum control circuit will send all airflow to the defroster outlets. This condition may occur during acceleration (slow leak), may exist at all times (large leak) and may happen only when certain specific functions are selected, indicating a leak in that portion of the circuit. ..." from F-150, F-250, F-350, F-Super Duty and Bronco, F-Super Duty Motorhome Chassis Workshop Manual
Source: by Ford


"...The vacuum hoses used in the passenger compartment control circuit are constructed from PVC plastic material. The vacuum hoses used in the engine compartment are constructed of Hytrel. Because of the materials used, the vacuum hoses should never be pinched off during diagnosis to locate a leak. Use Rotunda Vacuum Tester 014-R1054 or equivalent to locate vacuum leaks. A wood golf tee can be used as a plug when it is necessary to plug one end of a vacuum hose for leak test purposes..."
Source: by Ford


A/C Switches to Defrost in MAX Mode; "...If MAX A/C only blows out the defrost registers, or if it switches to defrost during hard acceleration, this vacuum line (to the recirculate motor) is the reason. The white plastic is far more susceptible to UV light than any other color, and the gap along the edge of the hood allows it to degrade..."
Source: by Steve83



Air Conditioning Control Diagrams & Overview in 92-96; "...In the OFF position, all doors are in the vacuum-applied position with the exception of the PANEL door. The blower & compressor clutch circuits are not energized. In the MAX A/C position, all vacuum operated doors are in the vacuum position. A/C damper inlet door (19C802) air is shut off and the passenger compartment air is recirculated to maximize cooling. Discharge is through panel register. A/C clutch & blower circuits are energized. In the NORM A/C position, outside air is allowed to enter the passenger compartment. The air passes through the A/C evaporator core (19860) and is cooled before reaching the passenger compartment. Discharge is through panel register. A/C clutch & blower circuits are energized. Ventilation is delivered through the instrument panel registers when the function selector knob in the A/C control (19980) is set in the VENT position. In the VENT position, no vacuum is applied to the OUTSIDE/RECIRC. vacuum control motor (18A318 ) and the door is open to the outside. The air coming in through the cowl is discharged through the panel registers. The blower circuit is energized, but the A/C clutch is not. In the FLOOR position, no vacuum is applied to the vacuum control motor and the OUTSIDE/RECIRC. door is open to the outside. Air is discharged through the heater outlet floor ducts (18C433) with a small amount going to the windshield defroster hose nozzles (18490). The blower circuit is energized, but the A/C clutch is not. In the MIX position, outside air is discharged through the windshield defroster hose nozzles and the heater outlet floor ducts. A/C clutch & blower circuits are energized. In the DEFROST position, outside air is discharged through the windshield defroster hose nozzles with a small amount going to the heater outlet floor ducts. All doors are in the no vacuum position. A/C clutch is engaged in ambient temperatures above approximately 10�C (50�F) & the blower circuit is energized. The PANEL/FLOOR, FLOOR/DEFROST and OUTSIDE/RECIRC doors are vacuum operated. For maximum cooling, the temperature knob should be set in its fully counterclockwise position; the function knob should be in the MAX A/C position; and the blower motor (18527) should be set for a desired rate of airflow. Even though the function knob is on MAX A/C, the temperature knob, being manually controlled, may be set to modify the temperature of the air and the path through which the air flows. Another characteristic of the MAX A/C setting is the increased noise level of the blower motor. Speed does not change when the OUTSIDE/RECIRC. door is moved to either of its two positions. The difference in noise level is that an open recirculation door exposes the passenger compartment directly to the noise. When insulated against the noise with the recirculation passageway closed, the speed appears to be less. The control knob operates an A/C switch that is attached to the backside of the A/C control by one screw and retainer tabs. Five hoses (black, white, red, blue, yellow) extend from the A/C control just below the electrical connector for the mode selector switch to the vacuum control motors and vacuum supply. The solid black hose goes to the vacuum supply through a tee-shaped A/C vacuum check valve (19A563), which attaches the A/C vacuum reservoir tank and bracket (19A566) and engine source. The white hose actuates the OUTSIDE/RECIRC. air door two-position vacuum control motor. The blue hose actuates the FLOOR/PANEL air door two-position vacuum control motor. The red and yellow hoses actuate the FLOOR/DEFROST three-position air vacuum control motor. Each end of each hose slides onto the nipple of the vacuum port to which it attaches..." SEE DIAGRAMS
Source: by Steve83



Vacuum Leak Test; On an idling engine check for vacuum leaks using a mechanic's stethoscope with the probe removed, or a ~3' garden hose section. Don't spray flammables on a running engine. MIESK5 NOTE; Also check: vacuum hoses; intake manifold gasket & throttle body; PCV line; vacuum reservoirs: EGR Sys Vacuum Tank & 2ndry air (coffee can); AC, heater, defroster, vent control ckt & vacuum tank (plastic ball type), under dash & lines to heat/blend/etc. doors; power brake booster; cruise control ckt, etc.... where applicable; (combined w/ Steve83's info, thnx) BEWARE OF BELTS/PULLEYS, FAN AND HOT ENGINE
Source: by miesk5 & Steve83 at Ford Bronco Zone Forums

Vacuum Line Acronyms & Color Codes; EMISSION: Red = Main vacuum; Green = EGR function; Orange = Heat control Valve (exhaust & intake) (AKA heat riser but more complex); Yellow = from the TAD Solenoid (driver's side Forward Solenoid) to the TAD (Diverter) Valve located at the rear of the Intake Manifold (Distributor Advance in Carbureted Engines); White = EGR vacuum (source); Black = Mainly used for the Evaporative emissions control; Black = Thermactor ACV or Diverter valve; Blue = Throttle Kicker control; Pink = from the TAB Solenoid (driver's side rear solenoid) to the bottom of the Thermactor Air Bypass Valve (TAB or BPV/AIR Bypass (AIRB) valve); ACV (Air Control Valve) is the TAD (Thermactor Air Diverter) Valve (AIR Bypass (AIRB) and AIR Diverter (AIRD) valve combinations); MAN VAC is Manifold Vacuum; FPR is Fuel Pressure Regulator; EGR is Exhaust Gas Re-circulation Valve SOL V: Thermactor Air Diverter (TAD) Solenoid (SOL V) (AIRD) & Thermactor Air Bypass (TAB) Solenoid; ; EVR is EGR Vacuum Regulator; VRESER is the Vacuum Reservoir Can (Tank); V REST on later years is Vapor Valve (Roll-Over @ Gas tank); V REST on earlier years such as 78/79 & SEABRONC's 83 is a Vacuum Restictor/Delay Valve, it restricts vacuum for a certain amount of time, on most engines a vacuum line from the carburetor base runs to a T & then to V REST to the distributor; Carbon Can is Carbon Canister (Charcoal Canister, Vapor Canister, Evaporative Emission (EVAP) Canister); MAP is Manifold Absolute Pressure Sensor; AIR BPV is the AIR Bypass (AIRB) Valve, also called the TAB (Thermactor Air Bypass) Valve; CPRV is Canister Purge Solenoid Valve/ Canister Purge Solenoid (CANP); VCKV is Vacuum Check Valve; CAT is catalytic converter; ENG is engine; PCV is Positive Crankcase Ventilation Valve. HVAC in 92-96; Black = from engine source to vacuum check valve & to vacuum reservoir tank & to Control Panel; White = actuates the Outside/Recirc air door two-position vacuum control motor; Blue = Mix (actuates the FLOOR/PANEL air door two-position vacuum control motor); Red = Floor Flow & Yellow = Panel, (actuate the FLOOR/DEFROST three-position air vacuum control motor). READ MORE
Source: by Steve83 (Steve, That dirty old truck), Seabronc (Rosie, Fred W), Seattle FSB & miesk5 at Ford Bronco Zone Forums


Vacuum Hose Harness Pic in 80-96; "...80-96 similar, except 87-early 88 w/factory air; The 80-86 vacuum tank is a plastic ball on the R wheelwell..."
Source: by Steve83

96 XL 5.0 E4OD, Man Xfer/Hubs
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THANKS to ALL WHO SERVE!

my broncolinks.com was "disturbed"; but some sections are archived @ [url]http://web.archive.org/web/20121009110424/http://www.broncolinks.com/index.php
select a LINK, Right Click & Hit Properties; copy the second HTTP address; paste in a new browser window or Tab to see original page


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post #5 of 9 (permalink) Old 10-13-2010, 10:00 AM Thread Starter
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Okay, thanks everyone! I'll get down & dirty and start checking it out and post what I find out.

BB
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post #6 of 9 (permalink) Old 10-13-2010, 10:51 AM
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There is a small plastic vacuum reservoir on the blower motor case on the passenger side of the engine compartment. This is the main reservoir for the HVAC system. Mine was cracked by a PO who attempted to fix it with epoxy. I used a hand held vacuum pump/gauge to test the circuit.
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post #7 of 9 (permalink) Old 10-13-2010, 10:53 PM
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Quote:
Originally Posted by biederboat View Post
When I get on the gas (e.g. going up hill), I lose air flow coming out of the vents (with or without a/c). I know these lines are vacuum operated but I can find or hear any leaks (including the white line). Is there any way to pinpoint this? Do I just need to look harder? Most of the time air flows just fine out of the vents, it's only temporarily lost while stepping on the gas.

Thanks,
BB
IF you send me your e-mail i can send you a complete vacuum diagram.

"JUICE"
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post #8 of 9 (permalink) Old 10-14-2010, 11:02 AM
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yo;

from FORD EVTM by Bronco Rob

96 XL 5.0 E4OD, Man Xfer/Hubs
USN & DoD Planner (ret)
THANKS to ALL WHO SERVE!

my broncolinks.com was "disturbed"; but some sections are archived @ [url]http://web.archive.org/web/20121009110424/http://www.broncolinks.com/index.php
select a LINK, Right Click & Hit Properties; copy the second HTTP address; paste in a new browser window or Tab to see original page


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post #9 of 9 (permalink) Old 07-12-2015, 11:24 AM
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I had the same problem with my 96 XLT 302, I check all the vacuum lines with no luck, after a some time looking for the leak with no results I just decided to replace everything that has to do with the vacuum, I started by the cheapest and easiest, which was the throttle body gasket, which was really dry, had a crack and was there since it came out of the factory. As soon as I started the truck I could feel a difference in the acceleration and the vents didn't switch to defroster anymore. I bought the whole intake plenum gasket set and will be replacing all of them at some point just to be sure.
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