Bypassing the heater core in the summer

I'm cross-posting this from the ISSF. The '91 B-bodies had a vacuum-operated heater core bypass valve that kept the heater core deactivated when the temp knob was turned to cold. I've pondered swapping it in to help my cabin run cooler in the summer, but to be honest, the '91 B-body valve is an ugly octopus and a plumbing nightmare.

I just popped my head under the hood of a coworker's '97 Ranger and the heater bypass valve is elegant and simple. This would probably be easier to splice into the lines than the '91 B-car setup. It appears to be common to the '96-2000 Ford Ranger or Explorer. The '91 Caprice one took up a lot more space than this one does. You could probably cut the hoses and add the valve in directly over the upper control arm where you've got lots of room. Retrofitting the '91 B-body valve looked a lot more tricky, and in a more constrained space.

Now granted, you still have to figure out a way to control it, but probably an Aquarium supply store valve hooked into the HVAC vacuum supply via a T, put it in the ashtray area, and you could control it manually from the driver's seat.

An electrical option would be to grab an EGR or EVAP solenoid off a junkyard B-body and run a switch with it (although I don't know how those solenoids would hold up under 100% duty cycle for long periods). That way you'd keep all of the vacuum piping under the hood and just run a wire into the cabin to control it.

I don't have time this summer to engineer this, but it's a nifty project. It looks like the pipe sizes are close if not identical to the B-body heater hoses.

Autozone sells it as an Everco heater control valve, PN 74809, $18.

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It is located on the passenger side of the truck, right where stock B-body heater core hoses would be.

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I already addressed this somewhere else, but here's the short version.

Last summer, I helped a friend do the heater core bypass mod to his Ford truck. Before he did it, the AC blew hot air. After he did it, the AC blew cold air. It made a huge difference. I thought about doing it to the Roadmaster, but the Roadmaster AC already blows cold air.

I also wonder if the heater core is part of an automatic defrost that keeps the AC coils from frosting up.

My 91 OCC is blowing a very comfortable 44 degrees with the temp set to 65 and fan set at
whatever speed it chooses.Once the car cools down inside the climate control sets the fan at
a quiet speed and everything settles down real nice.This is the first car that I have owned
with automatic climate control that works this damn good.I like it a lot and the only freon
I use is Artic Freeze and there is a difference.
Jim Gordon

If you look at the vacuum schematic, you may be able to tap into the same line that the OEM part uses. The system shuts a door to the heater core in AC mode. The same circuit could be used to shut the water off if the port is not available on the distribution valve.

Fred Kiehl wrote:

If you look at the vacuum schematic, you may be able to tap into the same line that the OEM part uses. The system shuts a door to the heater core in AC mode. The same circuit could be used to shut the water off if the port is not available on the distribution valve.

This is exactly what I was thinking. Unfortunately it sounds like the Caprice guys are out of luck, as only the Roadmaster with the automatic climate control would have this ability.

Hope evercool has done a better job of this valve than Ford did. Had the identical valve in my 87 Crown Vic. Average life expectancy was 18 months. Damn things would harden with age and then crack. At least I didn't have to remember when to change the coolent. The car did it for me.

Bill

Sounds like the antifreeze companys had a hand in making that part.Programmed destruction,
"a better idea"by Ford.
Jim Gordon

i think my wife's old 95 safari had a set up like this. i had to replace it when the flapper inside broke free inside (was making a vibrating noise was tough to figure out that noise). i now have 2 astr/safari o1 vans will check it out tomorrow. the 95 was a small set up and i would hate to put ford parts on my wagon

My first order of business when the sun rises in the morning is do bypass the core on my wife's Durango. AC in back gets nice and cold easy. AC in front not so much. And if you let it idle, well, the heater core leaks, so the AC gets hotter and the truck starts to overheat from not enough coolant pressure.

That and I think the fan clutch is toast.

But I've wrapped the underhood lines in reflective foam insulating tape and I'll bypass the heater core with a 3/4" male/male coupler and a pair of clamps. If this solves either the AC or hot running problem, I'll consider it a victory. If it makes the hot running worse but fixes the air, I know to go for that fan clutch next. Water pump and radiator are both new along with all hoses. So if it's not the fan clutch, might be a slightly blown motor. No smoke, no bubbles in the top hose, but it could be leaking just enough to heat it up at idle. Runs cool above 40mph no matter what, and AC cools down decently too. Washed the grunge out of the condenser but no change.

I hope the heater core bypass solves this. I'll buy a $700 beater with a heater for wintertime whether wife approves or not. But this truck has cold AC and we need to take advantage of it while we can.