I own a 20 year old Ford Aerostar van. It has a 3.0L V6 that has cooling issues. That model had issues from the beginning. In the middle of the model year Ford added and rerouted cooling hoses, but even that didn't fix the basic problem of not enough air flow over the engine. So, even when I had working a/c, I couldn't run it in really hot weather when it was most needed.
The a/c failed last year and I left off repairing it because of the age of the vehicle and the basic unsolved cooling issues.
The van has two sliding windows, one on each side just behind the front seats. Those are manual, and don't do a very good job of cooling the van.
I added an inverter and window a/c intending to blow some cool air on me while making short trips, but a window a/c isn't ducted to vent the hot air when it's sitting inside a closed box like my van.
What I really needed was a hole in the roof to vent hot air out. Since the van is old and paid for, I can afford to take chances making body mods to it.
Step 1: The Parts Needed
I ordered a standard size RV vent from eBay. It was less than $40. It's the industry standard 14 1/2" square and comes with a small 12vdc fan. It did not come with mounting screws or gaskets or a garnish ring and was not painted.
I went to a local auto supply and bought a roll of 1" wide peel and stick foam camper tape and a spray can of rubberized undercoating.
I have a reciprocating saw with metal blades, a 3/8" variable speed drill and metal bits and an assortment of aluminum pop rivets. The holes in the vent mounting ring are 1/4" so I used 3/16" diameter pop rivets.
Step 2: One Unexpected Hurdle
I stood on a ladder and looked on the van roof for a place to put the vent and then remembered that the roof has channels front to back to channel and shed water. I preferred a flat surface to mount, but there was no place to put the vent that would not cross at least one channel. The channels are about 1/2" deep and will leak if not sealed well, so I moved the vent a little off center so only one channel had to be cut. There is a light in the back, too, and I didn't want to move it. I did not consider that there might be lateral roof reinforcing channels under the van headliner. The postion I chose cut through one of those. I don't use the roof for carrying stuff, both the back benches are out in storage, so it didn't do real harm to remove one cross member. No one sits back there, and in a roll over the van would be totalled anyway even if the roof held.
Step 3: Mark and Cut
I put down a drop sheet inside to catch the stuff that fell when drilling and cutting. Using a yardstick and permanent marker I made a 14" square on the roof and drilled holes at the corners so I could make 4 straight cuts with the saw.
After cutting out the hole, I checked the fit and it was correct. The vent MUST open to face backwards or if it is open while in motion it will be ripped off by the wind.
The underside of the vent has two layers of foam seal stripping to form a compression seal. I added a third layer directly to the outside of the finished cut hole.
Step 4: Drill and Rivet, Then Seal
Using a 1/4" drill to make holes and 3/16" aluminum rivets I carefully cinched down the vent. Once riveted down I sprayed around the underside of the cap with underbody coating. The rivet holes will leak and the exposed metal will rust if not sealed.
I didn't buy a garnish ring and may skip making one. This van isn't pretty. I haven't wired up the fan. I intend to add a solar panel to the roof to boost the vehicle power output to help run the window a/c in stop and go traffic.
If I do that I may hook up the fan to run directly from the panel's charge controller. I have the controller already.