On my 90 5.8 there is a vacuum can underneath the plastic rad overflow tank. I see no hoses connected to it nor do i see any in the vicinity that should hook to it. I have searched the threads but cant find any about a can in this location. The truck is not showing any codes but i am wondering if this can has anything to do with my air/heat system not working well

 

I have a 90 5.8 and I just went and looked and took some photos. It's definitely hooked up - it was cold and snowing outside so I couldn't get in there and follow it everywhere but to the best of my ability it seems like there are two lines coming from that can. I cannot see where the second one hooks up because I can't see under the coolant recovery tank. But the one I can see coming out of the front of the can the can tees off and goes towards the motor, then loops around and goes to the cruise control. As far as the one that I could not see under the tank, it appears to go through the firewall into the truck and is probably for the heat/AC vent controls. But I'm not positive. So yes, that can is definitely used and could definitely cause problems with the heat and a/c not blowing right. If you have cruise control that doesn't work then this would explain that too. I'll be posting photos as soon as I reply to this, hopefully they will help you.

 

These pictures are from a 1990 5.8 auto trans. You cannot see the line that goes under the tank but I -think- that connects on the other side of the can and I think that it's the one that goes into the firewall. I tried to feel in there but I couldn't locate it's source. In the first photo you can see the tee that the line coming from the front of the tank goes to, and in another one of the pics you can see where it loops into the bracket and then goes into the cruise control. So I think that the one coming from the front of the tank is for the cruise control - the tee to the motor is where it gets it's vacuum from for the cruise control and the tank holds the vacuuum reserve. For the second line, you can see in one of the pictures how it goes through the firewall. That's where I -think- the second line goes anyway, I cannot see for sure because I can't see it at either end. But it makes sense that it could be giving vacuum to the AC/heat controls, because I don't know of anything else inside the truck that needs vacuum besides those. Were it warm and sunny outside instead of cold and snowing I would have gotten up in the engine bay to find out for sure but you'll have to work with my description and these photos for now. I hope they help you!

And please note that, from what I've seen, if that vacuum tank is not connected it would cause a lot of problems.

 

Yes, on your 1990 truck the can under the WSW/overflow tank supplies the cruise servo. In 1993 Ford changed to the electronically modulated cruise servo so from that point forward there would be no can in that location. They used that spot for the 4 wheel ABS system control box.

dn.

 

What about the one that seems to be coming from the other side of the can and appears to go through the firewall? Is that still part of the cruise control or is it for the vents? Either way, unless plugged somewhere, he's got a big vacuum leak and that right there would cause problems with the A/C/heat control. A vacuum leak anywhere can do that.

 

thanks for the responses. Looks like i need to look for some vacuum lines. The cruse control worked when I brought it down here I did replace the rad hoses and trans cooler lines maybe i knocked it loose while working on that. Havent tried the cruse since will do that tomorrow

 

Thanks for the pics neither one of my manuals showed anything for this or if they did i was too dense to understand it

 

My cruise servo connects directly to the christmas tree on the intake but i think i found the problem with the heater a broken line going to the acuator on the heater door. I still find nothing that will connect to that can. Maybe i changed things around when i put the 95 motor in just dont remember

 

Success! repairing the damaged white vaccum line fixed all the ac/defroster problems and took the annoying surge out of the idle. Everything works as it should now except now i notice my ac unit needs freon but thats an easy fix

 

Oh you put a 95 motor in. You didn't say that. Big difference as far as the cruise control vacuum since the '95 uses electronic cruise control. But I'm glad you got your vents working properly and fixed the surge. A missing vacuum line will certainly do those things.