1988 7.3 Air Conditioner Vacuum Tank Mess

[Ray Cecil]

Hey. I've been having to wait a long time for my air to switch from defrost to the dash vents. So, I figured I'd investigate.

I could hear a vacuum leak once I shut off the engine. So I knew we had a leak somewhere.

I did the old smoke technique with a cigar and quickly found the leak here....



But wait...what the....something doesn't look right...at first I thought this was part of the box, and upon closer inspection I found this....



Yup, that's a vacuum tank. It's designed to fit right onto the side of the blower box. First I've ever seen this style. I'm used to the coffee can or black plastic ball....

So I cleaned it up and attempted a 3M gasket....which failed miserably.





So....I kept the 3M on there, and applied some weatherstripping adhesive around it. It's currently setting up.

However....I plugged the hose that was going to this tank. Everything in the dash worked much better and quicker.

Why do I need this vacuum tank again???

[85lebaront2]

Ray, probably not on a Diesel, you should have a mechanical vacuum pump so it just pumps faster as the engine speeds up, just like my two Diesel GM cars.

[Gary Lewis]

As Bill said you may not need a reservoir on a diesel.  The gas engines use manifold vacuum and a reservoir is needed to keep things in the right mode when you accelerate hard and the vacuum goes away.  But with your vacuum pump I don't see the need.

And if you do need one you can just use one of the old juice cans or the ball reservoirs.

[grumpin]

My first thought was its there because it is a diesel.

I thought the vacuum pump on the 7.3 IDI I used to own was lacking.

[Ray Cecil]

Unless Ford just liked putting parts into a truck for no reason at all....I'm inclined to keep it.

I noticed awhile back when I first start the truck, it took about 30 seconds for the vacuum to build enough for my brake booster to function well. That's when I started noticing the damper door delay as well.

Plugging that vacuum line solved the damper door slowness. But I did not test the brake vacuum boosting. I'll do that later and see if it's improved.

I stuck it back on last night and am letting the adhesive cure really well before I pull vacuum on it.

I have a few other components under the hood on this truck I'm not sure what they do. I'll post some more pics in my other thread. We can keep this one focused on diesel vacuum components for the internet searches.

BTW I was at an autozone recently, and the guy in line before me was working on a 86 bullnose. They searched on the autozone computer and pulled up this forum for reference on a fuel related issue. I kinda chuckled.

[Ray Cecil]

grumpin wrote

My first thought was its there because it is a diesel.

I thought the vacuum pump on the 7.3 IDI I used to own was lacking.

Yes, I feel the vacuum pump is lacking. It's good enough for hvac. So, I'll probably be doing hydroboost in the near future.

[Gary Lewis]

That HVAC plenum was used on both gas and diesel trucks, so the vacuum reservoir was needed for the gassers. I am using the one from the 1990 truck I put on Big Blue. It is nice, but I’m not sure it is a requirement on a diesel.

As for the website, I’m glad it is helping others. 👍