Hello All, I have '96 bronco EB, the blower redirects when I drop the hammer or pull a load, but comes right back? I'm thinking vacuum? but unsure. Any help.

 

I'm pretty sure it is normal for the A/c to quit when under load especially when going up hills. it has something to do with the compressor clutch disengaging to give the added horsepower.

 

Problem is, it doesn't quit, it blows to the floor or defrost, A/C is still on? And it will happen even when I pull away from a red light, higher accelerations than normal?

 

You have a vacuum leak. The A/C is not shutting down - the air defaults to the floor/defrost when this happens. Check it next time. I think that it is designed to do this from the factory, when the engine vaccum is low it reverts to floor/defrost. How that helps the vacuum, I don't know. But it should not do it unless under an extreme load, like climbing and having the pedal pretty much floored ( a situation known to most Bronco owners) If it happens to easily then you have a vacuum leak.

 

Any ideas on how to find this leak, or where to start? Or how to test to see if vacuum levels are normal and maybe I just have a heavy foot? very possible!

 

Mine did the same thing. First I took someone's suggestion and bought a tester for under $30 at Auto Zone called a MihtyVac. I wish I had bought it years ago. It will pump a vacuum like using a caulking gun and has a guage. Start at a funny little thing between the evaporator box and the engine. It looks like a Tee with a little mushroom on it. Three hoses go to it. On my '94 Bronco 5.8 one little hose goes from that little check valve assy. into the vacuum reservoir that is moulded into the side of the evaporator box by the transmission dip stick. That hose had a hole in it so I cut and slipped a small hose on the cut ends to patch it. It takes several pumps to test the reservoir. Next test the little black hose from the check valve going into the firewall into all your A/C control *****. Pull a vacuum to 20 in. and see if it holds a minute. Then change a **** setting inside and pump it up and then test ALL settings. That will test all the hoses and vacuum actuators to all the doors. Mine were fine. Finally I found that little check valve was not holding vacuum. the purpose is to hold the vacuum to the A/C actuators and reservoir up (say around 20 inches) even when your engine gets under load vacuum may drop to (say 5 inches of vacuum). If the check valve is not working it may let your panel air go to the default defroster in the absence of good vacuum. That check valve assy holds the vacuum high for the controls. It only cost $11 at the Ford dealer. Now it will freeze me out no matter where or how I drive.

 

Perfect, I will try this tomarrow as some as I can get to the Zone, thanks

 

You wouldn't happen to have a Ford part number on that check valve would you????

Or.....is this the part we are talking about???

 

I threw the old part and box away. The description was Valve assy. Your picture is very close but not exact and yours might do the exact same thing. I don't know. The larger hose goes to the engine, the smaller to the A/C controls vacuum reservoir on the side of the evaporator box and to the A/C controls in the cab running beside the white hose. On my part the small connection went straight down opposite the large connection and the other small connection teed off it at a right angle. The top of the little mushroom part is black and the rest is beige.

 

of the engine compartment that comes from the passenger compartment. Both my 90 and a friends 92 were doing the same thing and it was due to in-leakage from a cracked/worn out vacuum line.

I sleeved mine with regular vacuum hose and he actually used heat-shrink over his.

I eventually replaced all the plastic line in the engine compartment with regular vacuum hose. That plastic line seems to get hard and brittle inside the engine compartment and then fail.

 

You are correct but I would still get the MihtyVac tester from A.Z. to test the check valve to the A/C controls and all the componets by checking each setting on your A/C and heat controls. Even with no hose or component leaks the vacuum will drop very low on long hills and the A/C will divert to defrost if the check valve is not working properly. A new valve was $11 at dealership.

I also found a straight vacuum leak that did not show up in pulling codes but by using the tester. My charcoal cannister purge selenoid valve was stuck open. Replacing it made a world of difference in throttle response and milage. That sucker--(it really did suck bad)---was almost $50 at the dealer but worth it. On my '94/351 it is secured next to the EGR valve with a cable tie.

 

Its not that it helps or hinders the vacuum operation, its due to the fact that the floor/defrost position is the default position for the air directing vanes in the system and this position is where they end up when ZERO VACUUM is applied to the dashpots that control them. The control handle redirects vacuum to the various dashpots buried in the dashboard to change the positioning of the air vanes when something OTHER than floor/defrost is selected.