Only blows air through Defrost.

[aeberwein]

Just bought a 2000 Ranger xlt about 170,000 miles on it. Project truck for oldest boy. The AC works, but only blows air out of the defrost. I have check all of the visible vacuum lines and there seems to be no leaks. The vacuum chamber seems to hold vacuum. Where should I go from here? The only place I did not really check was right at the firewall coming into the cab from the engine side. I would have to remove quite a few things to do so. Any suggestions are welcome thanks!!!

 

[rusty ol ranger]

Does heat come thru other places?

 

[rubydist]

Somewhere there is a vacuum leak on the line to the hvac controls - the defrost is the default position, so when there is no vacuum to the controls, you always get defrost air. The leak could be anywhere, but in my experience is more likely under the hood than in the cab.

 

[Dirtman]

Air is 70% nitrogen...

 

[RonD]

You can see the firewall vacuum line pass thru from cab side, under glove box, should be 2 vacuum lines, one is from vacuum reservoir(vacuum source), the other is vacuum OUT to the heater hose by-pass valve in engine bay

When you select MAX AC the heater hose by-pass is activated so no hot coolant passes thru the heater core inside the cab, just FYI

The Vacuum reservoir should have 2 vacuum lines
One comes from the intake manifold(vacuum source)
The other runs to the firewall and then to the climate control panel's Vent selector(defrost, panel, floor)
Defrost is the default position, as said above, no vacuum = defrost

The vacuum reservoir may have a built in Check Valve, so the hoses must go on specific ports
Or there may be an inline check valve on the hose that runs to the intake manifold
With engine running make sure you have vacuum at the reservoir, if not then follow the hose back up to intake

There is also a vacuum manifold behind the dash, fold glove box down all the way and look to the left, you should see multi-colored vacuum lines, this is the vacuum distribution for the vents and source

 

[aeberwein]

You can see the firewall vacuum line pass thru from cab side, under glove box, should be 2 vacuum lines, one is from vacuum reservoir(vacuum source), the other is vacuum OUT to the heater hose by-pass valve in engine bay

When you select MAX AC the heater hose by-pass is activated so no hot coolant passes thru the heater core inside the cab, just FYI

The Vacuum reservoir should have 2 vacuum lines
One comes from the intake manifold(vacuum source)
The other runs to the firewall and then to the climate control panel's Vent selector(defrost, panel, floor)
Defrost is the default position, as said above, no vacuum = defrost

The vacuum reservoir may have a built in Check Valve, so the hoses must go on specific ports
Or there may be an inline check valve on the hose that runs to the intake manifold
With engine running make sure you have vacuum at the reservoir, if not then follow the hose back up to intake

There is also a vacuum manifold behind the dash, fold glove box down all the way and look to the left, you should see multi-colored vacuum lines, this is the vacuum distribution for the vents and source

I have also read that the 4wheel drive has a vacuum supply also? If that would have a leek could that have an effect on the HVAC system? There is also a small chamber that is connected in line with a coolant hose that has a vacuum line going to it. Could that have a bad diaphragm causing it to not work properly?.

 

[Curious Hound]

There is also a small chamber that is connected in line with a coolant hose that has a vacuum line going to it. Could that have a bad diaphragm causing it to not work properly?.

That's the heater bypass valve that RonD mentioned. Easy to test. Disconnect the vacuum line and seal it (the end of the hose) so it can't leak.

 

[RonD]

Yes, 1998-2000 Ranger 4x4s used PVH(pulse vacuum hubs) and it has a vacuum solenoid hooked to a "T" on the vacuum reservoir hose, if it was disconnected it might cause low vacuum in the cab but I wouldn't think full defrost

No, on the grey vacuum line on the heater hose by pass in engine bay, it only has vacuum in MAX AC setting and shouldn't drop vacuum to 0 if unplugged

From your description you have 0 vacuum in the cab