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ford: 1992 f0rd e250 van 351w when going up hill pulling caming

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1992 f0rd e250 van 351w when going up hill pulling caming trailer air conditiner goes off
the air gets rerouted somewere als going down hill it coms back no load i checked a lot of things i think it is a low vacum problom under exseloration
Ok is the ac blowing out ok volume wise just stops blowing out of the vents and instead out of the defroster? It still blows cold just an issue with what vents its blowing out of?
Customer: replied 4 years ago.
defrost vents i dident notis if its cold
Yes there should be a check valve for the vacuum supply line coming off the intake manifold and runs to the vacuum tank near the ac evaporator box, if there is a leak in this supply line or vacuum tank it will default to defrost under a load or if the check valve is weak.


A TSB for replacing the vacuum tank helps show the check valve below:
The original vacuum tank with its check valve is located on the underside of the heater/evaporator assembly case inside the engine compartment. The vacuum tank is sonically welded to the case in an inaccessible location. ACTION:
If replacement of the vacuum tank is necessary, the original vacuum tank and check valve should not be removed from the vehicle. However, inside the right side passenger compartment, next to the heater assembly, at the lower front engine wall, a black vacuum hose leading to the check valve should be pulled off the old vacuum check valve and connected to the open port of the new check valve. Refer to the following Service Procedure for details.


1.In the passenger compartment, remove the right cowl side trim panel as covered in section 1-05B of the 1992 or 1993 service manual

At the lower right side of the blower assembly, pull the bullet style grommet containing the black vacuum hose straight back until it slips off the check valve. Pull the hose into the compartment, refer to Figure 1.
3.Remove and discard the long vacuum hose from the new check valve (F2UZ-19D848-A).
4.Select a new 1/8" (3.175 mm) I.D. vacuum hose of appropriate length to go from the vacuum check valve in the passenger compartment to the vacuum hose over the evaporator case and along the wall into the engine compartment. Connect this hose to the check valve where previously removed long vacuum hose was connected.
5.Route the new long vacuum hose through the grommet hole.
6.Disconnect the source vacuum hose at connector at top of evaporator in the engine compartment.
7.Connect the new vacuum hose to the source vacuum hose at the connector and secure.
8.Connect the vacuum hose (previously attached to the old check valve) to the open port of the new check valve.
9.Inside the passenger compartment, proceed as follows:
a.Position the new Vacuum Reservoir/Check Valve (F2UZ-19D848-A) to the cowl side area.
b.Mark the screw location.
c.Position the tank high enough so as not to interfere with side cowl trim panel when it is reinstalled
10.Drill approximate size hole for mounting screw to hold the vacuum tank
11.Put foam padding or strip caulk (dum-dum) on the tank to cushion it for a rattle-free mount on the sheet metal. Attach the tank.
12.Fill the grommet opening with strip caulk (dum-dum).
13.Replace cowl panel in passenger compartment. Make sure hoses are not pinched.
14.Verify proper operation of the system.
HDGENE, Ford Senior Master/Diesel/Trans
Category: Ford
Satisfied Customers: 4781
Experience: 25 years Auto experience, Ford ,GM, Chrysler, Asian & European
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Customer: replied 4 years ago.
Thank you for the research but this does not solve my problem. I have been over and over the whole vacuum system of my truck. All emissions check valves etc. test ok. I replaced the egr vacuum solenoid even though it wasn't bad. I will tell you why.

My truck has an external vacuum tank on the passengers side fender. There appears to be an internal check valve in the tank. It holds 19 in Hg after I shut the van off so I assume it is good. It has two lines on it. These go to a junction that splits off to the heater control system and goes through the firewall to the heater vacuum motors. There is no check valve setup like the diagram you sent.

I have traced the lines to the end and the culprit seems to be the egr vacuum control solenoid. It is normally venting vacuum to the atmosphere. I don't think it turns off the vacuum leak thereby depleting the vacuum supply from the reservoir. I have even tried to directly put a check valve on the a/c vacuum motor but the lines to the controls work together.
Customer: replied 4 years ago.
I don't know if this is a more modern setup or for a fleet vehicle or what. My van is in very good shape and I travel a lot with camping trailer. It is a conversion van. Is the egr solenoid supposed to vent all the time? It has 12 volts to ground.
Customer: replied 4 years ago.
Relist: Inaccurate answer.
Please refer to my explanation/reply from original answer.
It doesnt make sens for it to be hooked up to the evr solenoid for the egr valve,one line is a constant vacuumsupply and the other goes to the egr when commanded. You need to trace the black vacuum hose back from the vent panel/defrost mode switch and it should go to the vacuum tank as shown above unless you have a cutaway rv style van and anything goes in one of those, if not I will opt out and open this up to another expert and ask this to go to our rv experts
Customer: replied 4 years ago.
The vacuum tank has two lines a black and a red. the red is manifold vacuum and the black is from the internal vacuum tank check valve (out). These lines go to a connector under the hood that turns into three lines which one black one goes to the heater control. the other black line snakes around to all the various engine vacuum controls ending at the egr vacuum solenoid so if the vacuum solenoid is venting it eventually vents the vacuum tank thereby losing engine vacuum under load and closing the a/c vents. This is the only theory that I can come up with. It is all factory no mods. This is a conversion van but not a cutaway style van. This problem is driving me nuts! This appears to be a common problem on internet forums but no one has an answer.
Where does the black supply vacuum line go to from the back of the climate control panel?
Customer: replied 4 years ago.
To a three line connector that splits from the vacuum tank. Two lines are connected to the vacuum tank. They go to a connector that has a line going to the climate panel.
Ok you will need to hook up a vacuum gauge to the supply line going to the control head switch, while driving see if it has a constant vacuum, if it drops off, the check valve is no good or you have a leak in the system, if it holds constant vacuum then you have an issue with the control panel switch itself.
Customer: replied 4 years ago.
As I stated earlier the vacuum drops under load hills etc. especially while pulling trailer. It drops at all points but the check valve holds after you shut off engine. I have put vacuum hand pump to controls and doesn't lose vacuum through control panel. thanks.
Have you replaced the check valve? It can hold but be weak under a heavy load and we change them even if they check ok.
Customer: replied 4 years ago.
No I haven't. It's in the vacuum tank. Can I piggy back it with a universal?
Put another one in line just make sure it is hooked up in the correct direction to keep vacuum applied to the tank.
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HDGENE, Ford Senior Master/Diesel/Trans
Category: Ford
Satisfied Customers: 4781
Experience:  25 years Auto experience, Ford ,GM, Chrysler, Asian & European
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