Hey all,
I have a 2003 Ford ranger 2wd 6 cylinder 4.0
My AC has been having this issue for a while, sometime last year and now it's summer again. Anytime I accelerate rapidly or go uphill, the AC cuts off and I've read that could be a vacuum check valve issue. I just don't know where to look and even if I find this, what would I look for or test for?

Anyone else had this problem?

Thank you in advance!

 

The vents inside the cab are controlled by vacuum "motors".
Defrost vent is when there is NO Vacuum

Panel and floor vents both require vacuum to work

This is not related to AC or Heat, just VENTS

So when you accelerate the Fan/air blows out the Defrost vent instead of panel vent, correct?

In the engine bay, passenger side, at the firewall you will see TWO plastic vacuum lines, they can look like wires, but they are hard plastic vacuum lines
There will be a Black one and a Grey one
The grey one will run over to the engine and connect to the heater hose bypass valve

The Black one is the one for the Vents, follow it, with your fingers, it often breaks or cracks near exhaust pipes, it runs to the front of the engine bay and then goes down almost under front bumper
Its easily repaired with rubber vacuum hose of the right size, Ford uses plastic lines because its cheaper

It runs to a Vacuum reservoir located down low on front on passenger side, looks like a Black ball, it has two vacuum hoses connected
The Black line you just traced from firewall
And another black line that will run up to the engine, this is for the Vacuum Source and where a check valve "may" be located, you just have to follow the line up to the Intake Manifold

Intake manifold is the vacuum source, when you accelerate vacuum in the intake manifold drops down to almost 0
The vacuum reservoir(black ball) holds vacuum during this time so vents don't change to defrost.

If the black line to the cab is leaking or reservoir is cracked or check valve is bad, then there is no vacuum "reserve" so vacuum changes with throttle position

 

Wow thanks so much for the detailed reply, I'll have to check it out!

 

So I found the lines (I think) I didn't see any visible cracks or breaks, but did see what I think is a check valve that looks weird maybe?
The second pic just shows the black and grey wires that you mentioned.

 

Second pic is wires not vacuum hoses

EDIT OPPS yes those are the two vacuum hose to the right of the wires, black and grey hoses

This is a pic of the grey line connected to heater hoses: http://cyoum84abk-flywheel.netdna-ss...lve-layout.jpg

This is a 3.0l engine but only picture that was usable
In first picture it looks like grey vacuum hose is just under your hand

Find that on your 4.0l and follow it back to firewall, it goes thru firewall next to the Black vacuum hose

Yes, first picture may be vacuum lines, but Red, if you look at the label at the front of the engine bay it will have a vacuum diagram with colors

In 2003 the Check valve is probably inside the vacuum reservoir(part of it), not on a vacuum hose

 

So I followed the hoses as far as I could and didn't see any obvious defects. Is it challenging to replace the vacuum reservoir and see if something on the inside was broken?

Or is there a method of testing where a leak might be?

Either way, thanks for your info thus far, it's been helpful!

 

This is what the engine bay part of the system looks like: https://www.explorerforum.com/forums...nes-jpg.41662/

The large black ball is the reservoir, it has built in check valve
At the top of the picture is a Grommet with two vacuum lines and a white connector, that white connector is inside the cable, the grommet is in the firewall
(inside the cab there are two vacuum lines the run from white connector to Climate Control panel, if you had a leak inside the cab you would easily hear it)

You already know where grey hose runs

The black hose runs to reservoir, you need to find it, and then trace BOTH lines coming off of it, one of course runs to the firewall, the other to the engine, and it could as simple as hose is unplugged.

There is no simple way to do it, a mechanic would find the vacuum reservoir then unplug each hose and use a vacuum pump to tell if either line was leaking and then test the reservoir to see if it holds a vacuum

 

Thank you!

 

The grey hose is not plugged in! You said it plugs into the Heater hose bypass valve, any direction on where that is?

I plugged it in to the black object in the picture, which is directly behind the vacuum reservoir.

 

Yes, that looks like it, I don't know the plumbing on the 2003 specifically, it changes yearly, but that valve should be on a device with 4 hoses attached

You should have MAX AC back

The grey vacuum hose only has vacuum in MAX AC, it shuts off Hot Coolant flow thru the heater core in the cab and also shuts off fresh air vent(different hose)
If it was unplugged then that would cause vacuum loss but only when MAX AC was selected.

Just FYI, AC is only off or on, there is no high or low
MAX AC closes off fresh air vent and pulls in air from cab vent under glove box, so the AC is now cooling the already cooled air in the cab, instead of cooling the 90+ deg air coming in thru the fresh air vent, so MAX AC

 

Yep! Took for a good test drive and it's working wonderfully. Thank you so much for your patience and knowledge! Can't believe it was that simple.

 

Good work

Thank for posting the update and the FIX