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A/C and/or heater stuck on defrost

38K views 46 replies 19 participants last post by  MoovinTarget 
#1 ·
I have a 92 5.0 fs bronco.

the other month my a/c system got stuck in defrost mode. no matter the position of the switch it stays on defrost. A/C will still blow cold but only blow on with window. same goes for the heater.

I searched and found that people suggest its a vacuum line issue. Could someone please provide pics and/or specific locations of where these lines i should be looking at are.

thanks

P.S. I love the suggested related thread feature when u start to post a new thread! even better than searching!!!!! :thumbup
 
#3 ·
thanks for the info!
very helpful and precise

so i checked there and the line is in fine shape. nothing look out of the norm even soap and watered it to make sure there were no leaks. so now what?

EDIT: ok after poking around some more on the forums its suggested to look at the line that is hidden under the wire loom. so i shall do that tomorrow
 
#6 ·
Well you can physically move the lever to see if the actuator is locked up for starters.

And then you can start the truck (to get a vacuum source), and run a new line from a known vacuum source to the actuator.

Or you could buy a hand pump. Never used one.
 
#8 ·
White line?

Fender?

You lost me.

If the actuator isn't the problem, it is next most likely to be the HVAC controls themselves.
 
#10 ·
On the newer broncos, there are colored plastic lines that go to that vacumn actuator. They could be white also. they get very brittle when they get old. they will be hard plastic lines that go to the vacuum canister and possibly away from it. I had to replace those lines with rubber hose when it did the same thing.

Just look for some exposed white or colored plastic looking tubes. If you fiddle with them, they will most likely break apart, then you can follow the line and replace it with rubber. You can't get those lines replaced with original, for obvious reasons.

I would send pics of mine and where they are, but my bronco is being stored right now. So here are the pics from above with the areas circled where you might find these lines. (in my next post)
 
#11 ·
ok, well that copy/paste/circle/paste didn't work as easy as I thought.
oh, you white line goes into the fender? Is it about as big around as a pea maybe? 1/4 inch? That line should come out and connect to the vacuum canister (a ball or coffee can looking thing on the passenger fender)
 
#13 ·
i had a vaccume line knocked off behind the dash, take out the ashtray and ac controll panel and the glove box and see if you can hear a leak or see a tube that is not connected. mine was a yellow hose behind the ashtray that was knocked off of a vaccume actuator. i put it back on and was good to go.
 
#14 ·
Thank God I found this thread. My a/c has been pissing me off like a crazy. It blows cold for a while until all of a sudden it starts blowing in the defrost mode. I looked at that white plastic line and when I gently touched it it crumbled in my fingers, lol. I guess I know the source of the problem now :doh0715:
 
#15 ·
How's the easiest way to get behind the dash on a 92 Bronco? I have the same issue that just cropped up with mine.
 
#18 ·
Okay here we go again.;) Sorry if you think I am lazy but to me it makes sense.

I know I have to replace this little b.s. line with a rubber vacuum line. I can see obviously where it connects in the engine compartment. But does anyone know where it connects to after the fire wall? I really am avoiding tearing thru the embilical cord like cable just to make more work for myself later sorting it all back to the way it was.

At least if someone can tell me where it leads to (possibly with a pic) then I can just run the line and leave the old one to continue it's rotting until it's gone.:thumbup

Thanks.
 
#19 ·
Got to checking where this infamous little vacuum line runs off to, and I think I have found it. Could anyone confirm that this is that right one? My manual does not tell me shite! :doh0715:

White vacuum line:

Embilical that it runs into:

Where it runs into the FireWall:

Found it behind the glove box:

This is what I found running from the direction of the firewall:


Can anyone confirm that this is the right one?

Thanks:thumbup
 
#46 ·
91 Bronco doing same thing - Repair did not work



I have done the under hood repair of the white line. Now the vacuum is present but very weak. :banghead It takes about 5 seconds for the door to go from open to closed and vice-versa.

The AC still blows out the defrost if I manually open or close the actuator. I can hear and feel the door opening and closing. I do get a limited amount of air to the vents, but not much.

I followed the white line into the cab. It joins with a black line at a 3 way manifold behind the dash. Where is the vacuum for the white line sourced. Is it the line going to the evaporator core box under the hood?
 
#20 ·
my 87 is acting like this, been like this for awhile. panel vents work fine, switch to floor, panel vents are still on, switch to mix, floor vents come on, switch to defrost, mix comes on. this is probably what i'll have to look into, just don't want to have to tear the whole dash apart to fix it. my bronco is in my barn, not too road worthy at the moment.
 
#22 ·
I just fixed mine

While taking pictures of my 92 Bronco, I looked at the vacuum actuator and this is what I found.



I looked dusty and brittle so I pulled the rubber end peice off and noticed this.



I decided to do a quick fix to see if there may be other leaks so I did this



So Far, So Good. I drove for a few miles and didn't have the vent shift on me once.
 
#23 ·
Okay I finally got around to stopping by the local Advance Auto Parts store to pick up 6' of rubber vacuum line and 2 double male connectors. Got it in and it works like a champ. The a/c does not shut off at all anymore and I am happy as can be:thumbup

6' of rubber vacuum line:

2 double male connectors:

Where I ran the line up towards the top of the firewall where the antenna runs through:

See where it runs through above the firewall same as antenna?

This is where it comes out to the actuator:

Got the connector on and ready for boot:

Factory boot on and ready to connect:

Connected to actuator:

Spliced other end behind dash and added connector:

Slid right in with not trouble, DONE!

Hope this helps someone out, I wish I would have had access to something like this before when the problem started last year, lmao!
 
#24 ·
i know the hvac controls in the 87-91 model years and 92-96 model years are different designs, but don't they pretty much work the same?
 
#25 ·
I think so, but don't take my word for it. I would say revert to your manual but it does not have that information in it. Best bet is to either hunt for it in your truck or ask a member here with those years.

My way of fixing it may not be the most professional but it got the job done. I would have prefered to do replace the stock line completely and route it back through it's original location but:

1. I am lazy:goodfinge
2. Going through the firewall has always been a bitch:cry
3. And finally I am lazy:beer

I am just happy to have my a/c up and running again like it was factory new. It gets so hot and humid down here sometimes it is just unbearable.
 
#27 ·
On my 84' it was (still is) the actual flap inside that the actuator moves. One of the ends that it pivots on broke, so it sticks in one position or the other. I make it stay in vent during the summer and defrost/feet for winter. My local salvage yard won't sell the part I need without selling the entire duct system =$$$.
 
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