I have a 1998 Ford Ranger XLT 4X4 with the 3.0 V6.
Okay so I've read about the A/C only working through the defrost vents and it usually being caused by a vacuum leak. I am having that problem but can't seem to find the leak. I checked the reservoir behind the fender, checked the lines running from behind the engine over to the reservoir and to the unit under the glove box and all seems fine and dandy. I tried following the vacuum lines off where they split down below, where it appears they go to the brakes, and those all seem fine too. I used carb cleaner to check for leaks and tried to smoke (with a cigar, cheap way) with no success.
Another thing I want to point out is that when my truck hasn't been warmed up and I start the truck the vents work just fine and the correct settings work, until I try to change them. If I have them set to upper vents and cold air and start the truck they work but as soon as the truck warms up or I try to switch it to lower vents or A/C it goes back to defaulting to A/C through the defrost vents and wont change. The truck idles just fine as well and I can't smell or hear any abnormalities. My fear is there is a leak just small enough to cause an issue but not big enough to be found easily.
Any ideas on what may be causing this and if there is anywhere else I should check for a vacuum leak?
Okay so I've read about the A/C only working through the defrost vents and it usually being caused by a vacuum leak. I am having that problem but can't seem to find the leak. I checked the reservoir behind the fender, checked the lines running from behind the engine over to the reservoir and to the unit under the glove box and all seems fine and dandy. I tried following the vacuum lines off where they split down below, where it appears they go to the brakes, and those all seem fine too. I used carb cleaner to check for leaks and tried to smoke (with a cigar, cheap way) with no success.
Another thing I want to point out is that when my truck hasn't been warmed up and I start the truck the vents work just fine and the correct settings work, until I try to change them. If I have them set to upper vents and cold air and start the truck they work but as soon as the truck warms up or I try to switch it to lower vents or A/C it goes back to defaulting to A/C through the defrost vents and wont change. The truck idles just fine as well and I can't smell or hear any abnormalities. My fear is there is a leak just small enough to cause an issue but not big enough to be found easily.
Any ideas on what may be causing this and if there is anywhere else I should check for a vacuum leak?
RonD
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Welcome to the forum.
Vent selectors use what are called "vacuum motors", basically the "motor" pulls open a vent lever when it gets vacuum and a spring pushes vent closed when there is no vacuum at that "motor".
Default setting on all Ford vehicles is Defrost, so no vacuum = Defrost vent selected, so in Defrost all vacuum motors have no vacuum, either by choice or from a leak.
Example of Vacuum vent system here: https://www.ford-trucks.com/forums/a...ntid=517&stc=1
OK, for this system to work vacuum needs to be present and stable regardless of engine RPMs, that's the reason for the Vacuum reservoir, it is like the Power Brake booster, it is a Reservoir for vacuum so you always have vacuum for power assist braking.
Common complaint is that Vents will switch to Defrost setting while vehicle is accelerating, then back to "normal" at cruising speed.
Thats because intake manifold has very low vacuum when accelerating, vacuum comes back when cruising(or idling)
If this happens then it is usually vacuum reservoir issue or check valve
There should be 1 black line running from vacuum reservoir to the fire wall, pull this line off of the vacuum reservoir and suck on it, lol, yes thats the same as a vacuum.
It should HOLD a vacuum, hold negative pressure, like sucking on a straw with your finger over the end, NO LEAKS.
If there is a leak then follow that black line to firewall inspecting it very closely, this type of hard vacuum line will crack or melt(hear exhaust), it is easily repaired with rubber vacuum hose.
If black line is OK then you will need to go to inside the cab and find the connector for that black hose, pull that hose off and suck on it, you should hear the leak if its behind the panel or dash.
If black vacuum line holds vacuum then could be vacuum reservoir is cracked, not uncommon.
Reservoirs will often have a built in check valve, like power brake booster does.
Then makes the TWO hose connections specific, one MUST be hooked to black hose to cab
The other will have the check valve and connects to intake manifold
Some have in line check valve, it is on the hose to intake manifold
You should have a vacuum hose diagram on the radiator support, which will show the check valve if there is one.
They may also be a Grey vacuum line coming out of the firewall next to the Black one, the grey one will go to a Heater Hose vacuum valve, check it for leaks, i.e. suck on that hose :)
Vent selectors use what are called "vacuum motors", basically the "motor" pulls open a vent lever when it gets vacuum and a spring pushes vent closed when there is no vacuum at that "motor".
Default setting on all Ford vehicles is Defrost, so no vacuum = Defrost vent selected, so in Defrost all vacuum motors have no vacuum, either by choice or from a leak.
Example of Vacuum vent system here: https://www.ford-trucks.com/forums/a...ntid=517&stc=1
OK, for this system to work vacuum needs to be present and stable regardless of engine RPMs, that's the reason for the Vacuum reservoir, it is like the Power Brake booster, it is a Reservoir for vacuum so you always have vacuum for power assist braking.
Common complaint is that Vents will switch to Defrost setting while vehicle is accelerating, then back to "normal" at cruising speed.
Thats because intake manifold has very low vacuum when accelerating, vacuum comes back when cruising(or idling)
If this happens then it is usually vacuum reservoir issue or check valve
There should be 1 black line running from vacuum reservoir to the fire wall, pull this line off of the vacuum reservoir and suck on it, lol, yes thats the same as a vacuum.
It should HOLD a vacuum, hold negative pressure, like sucking on a straw with your finger over the end, NO LEAKS.
If there is a leak then follow that black line to firewall inspecting it very closely, this type of hard vacuum line will crack or melt(hear exhaust), it is easily repaired with rubber vacuum hose.
If black line is OK then you will need to go to inside the cab and find the connector for that black hose, pull that hose off and suck on it, you should hear the leak if its behind the panel or dash.
If black vacuum line holds vacuum then could be vacuum reservoir is cracked, not uncommon.
Reservoirs will often have a built in check valve, like power brake booster does.
Then makes the TWO hose connections specific, one MUST be hooked to black hose to cab
The other will have the check valve and connects to intake manifold
Some have in line check valve, it is on the hose to intake manifold
You should have a vacuum hose diagram on the radiator support, which will show the check valve if there is one.
They may also be a Grey vacuum line coming out of the firewall next to the Black one, the grey one will go to a Heater Hose vacuum valve, check it for leaks, i.e. suck on that hose :)
