Heater Bypass Mod: Cooler A/C!
 

Okay after searching around for random things on google a couple night ago, I ran across this thread:

https://www.ford-trucks.com/forums/9...ass-valve.html

It explains that the heater core can be bypass with a vacuum switch and that will cool down the inside of the cabin quite noticeably. I have never heard of anything like this on the Bronco forums and never thought about it before. The setup of the vacuum and heater core hoses seems the same on our broncos as in the 99-03 powerstroke trucks.

Anyways, here is the mod from 60RatRod semi-rewritten for our Broncos!

What this mod does is prevent coolant from flowing through the heater core when certain settings are chosen on the climate control on the dash. This makes a difference because in our stock Broncos, coolant is ALWAYS flowing through the heater core, and even when no heat setting is selected on the climate control switch, radiant heat from the heater core is being dissipated into the cabin. The air from the blower motor circulates right next to the heater core, so even if it is "sealed off" when you have the heat off, the heat still gets into the air and out through the vents. This mod aims to fix that.

Needed Supplies:

1. Auto Zone P/N 74809 Heater Core Bypass Valve for a 97 Ford Explorer V-6
2. 2 to 5 feet of 1/8 inch vacuum hose (depending on where you hook up the hose)
3. Four 7/8" thru 1" screw hose clamps
4. 1/8" vacuum "T" fitting

These pictures are from 60RatRods post:

The bypass valve
https://www.ford-trucks.com/user_gal...d=230217&.jpg=

All needed supplies
https://www.ford-trucks.com/user_gal...d=230215&.jpg=

Installation:

CAUTION Make sure your vehicle is cooled down before beginning because you will come in contact with coolant!!

The first thing you should do is cut your heater core hoses in half somewhere along the firewall. After they are open, you can take the bypass valve and hook the hoses up to it, securing it with the 4 clamps you have purchased. It does not matter what way the valve goes, as long as the hoses are "lined" up.

Here is where I installed mine:
http://i1267.photobucket.com/albums/...ps9690def1.jpg

After the valve is installed, determine where you want to hook up the vacuum hose.

I will proceed with the write-up with how I hooked it up, but later explain the other options.

I took the 1/8" t and connected it to the white vacuum line coming from the harness that normally goes into the re-circulation valve:
http://i1267.photobucket.com/albums/...ps63062b0e.jpg

I had to replace part of the vacuum line because my old one deteriorated away! If you have to do the same, just make sure you cut off enough where the remainder of the old line is still soft.

After that is connected, cut off enough of the extra vacuum hose you purchased and connect it to the bypass valve:
http://i1267.photobucket.com/albums/...psa327e56d.jpg

The last end goes to your re-circulation valve thing (I think that's what it's called. Basically this valve will is engage when the MAX AC is selected and makes it so that your cabin air is recirculated instead of pulling outside air.)
http://i1267.photobucket.com/albums/...psee5ddfe9.jpg


Once that is done, you finished! Now, when MAX AC is selected, that valve prevents coolant from going to the heater core so your AC will not be mixed with radiated hot air from the heater core! I don't have a temperature gauge to test this, but I know that it works quite well. Some people say 10-15* cooler from the vents and I believe it!

Now, the way it is set up here makes it only work with MAX AC, you can hook it up so it works with MAX AC, AC and VENT, but this will prevent the AC and defrost working at the same time. Hooking it up this way will make VENT and AC cooler though.

Here is a vacuum diagram explaining what color lines are connected to what on the climate control switch:
http://i1267.photobucket.com/albums/...ps9ec7e39a.jpg

To hook it up this way, you need to connect the vacuum line from the Heater Bypass Valve to the RED vacuum line underneath your dash. This means that you will have to route the vacuum line you purchased through the firewall and connect it find a place to connect it to the RED line. Here are some pictures of where to access the red line:
http://i1267.photobucket.com/albums/...ps5fbff718.jpg

This is the with the glove-box down, in the dark area, (my camera wouldn't flash right!:-arrgh) you can access the vacuum line from there.

With the ashtray pulled out, you can also access these lines, as you can see the red one in the picture:
http://i1267.photobucket.com/albums/...psf2a2c8d8.jpg


You would have to take off the ashtray assembly to get better access there, or you can try and access it from under the dash.

I decided not to go this route because I didn't want to have to route the hose through the firewall. However it may be something I do later so my VENT option seems feasible to use, because it always seems to blow hot air otherwise.

I hope some people find this useful because I sure know I did!

Awesome write up!!! I think I'm gonna try that one. SW Florida is so hot and humid, this will be a PLUS!! I wish I could remember what some A/C guys were doing at one of the Ford dealership here. They were doing some mods on the A/C system on some Super Duty trucks and they were blowing about 45 degrees!! I saw the thermostat!! I sat in one of them, and about 5 minutes is all I could stand!

Air Conditioning
 

Thanks!!! I printed this and put it on my list to do.

Thanks! Yeah this has helped my AC out... but shortly after my AC started to get warmer and I realized I have a leak in my semi-new AC system. I just recharged it and it works better than it has before thanks to the bypass mod. I just hope the leak gets sealed with the recharge kit since it says it has "lea sealer" in it. That's wishful thinking but I'll see how it goes!

Alright just an update now I got my AC recharged after that stupid leak. My AC is much colder than it ever used to be. I had it completely redone about 2 years ago and it feels quite a bit cooler than when it was new. The temperature reached 110 here yesterday and it didn't bother me with how cool my AC was running on the MAX setting so anyone who lives in hot weather should do this mod!!

A/C Modification
 

I'll take 37 degrees all Summer in Texas.

Roundtuit done. The A/C mod was successful for me today.
I read customer reviews for the 74809. Many reported leaks at the seams and coolant loss within a few months so I bought the Motorcraft YG 350 for $8 more dollars.

All readings with fully warmed up engine, 50mph, Max AC, Fan H. Temp on Coolest.

Before mod. temps
Ambient O/S 82 degrees
2" above hump 72
Vent below 4WD buttons 40

After mod. temps
Ambient O/S 89
2" above hump 71
Vent below 4WD buttons 37

Of course that's just shows a small drop in vent temp. I could not read the radiant heat reduction from the passenger side but the cab was much more comfortable with the mod.

Before installation I tested with my Myty Vac.
Valve shifted at 8 only inches.
Then I blew in the port to determine how it functions.
When activated with vacuum the coolant coming from the water pump is diverted back to the water "Tree". That generates the good thought that the ECT in the tree will continue to get information as originally designed. Putting a valve or valves in the heater hoses that just block the flow may cause performance issues. Back to blowing in the ports...it does not seal air tight, good, not perfect so there will be a little coolant going to the heater core. After the test drive, I could hold my finger on the blocked side hoses 7-8 seconds but only 3 seconds on the hot side hoses.

Before starting the mod the setting was Max AC. When I cut the hose to the recirculation motor it moved. That told me the check valve before the controls was working and there were no vacuum leaks in the control hoses. Note the white Tee added to the vacuum line that goes to the recirculation motor. That vacuum hose was originally white and comes out of the harness. Now it activates the recirculation motor and the new heater control valve.

There is an arrow on the bottom of the new valve by the nearest hose pointing away from the camera so I installed it this way thinking it is the flow direction from the water pump. My blow-in-it test confirmed it.

I did not try the temperature control but suspect we might get just a little temp increase while on Max AC due to the little leakage through the valve. I can't believe I am actually having the thought of possible wanting less cool. That tells you the mod works.

About thirty years ago a Ford mechanic who specialized in A/C advised...
Never use Lo fan speed, causes too much head pressure.
Always use Max to keep it clean.
Always use Max to remove moisture unless you are way out in a dry climate. We were 60 miles from the Gulf.

My fan preference is next to Lo, shall we call it 2? My alternator is not the best and higher fan speeds are hard on the battery in town.

Bubba Jones thanks again for sharing this with us. I'll take 37 degrees all Summer in Texas.

A/C paradox.
 

I'm still loving the mod.

Today I read the vent temp on high then changed the fan speed to "2" to see how much lower the temp would drop with air spending more time on the evaporator. To my surprise, the vent temp rose about 3 degrees!

Could the fan speed resistor in the fan housing be putting out that much heat?

Hmm I don't know.. I know my dad has a Yukon that had the resistor get really hot and start to melt some wiring (it was getting defective). I wouldn't think the resistor would get super hot normally though, but maybe a few degrees. I don't know where it is located exactly on the Bronco either... I"m interested in trying to find it and feel with my hand (around the resistor) to see if it changes.

I THINK I remember GS commenting it is in the fan housing and can be located by removing the fan.

Oh.. well if I have to remove the fan to check it out.. I may not be too inclined to test that. I had to replace the blower motor a while back and it was a pain getting it out with the vacuum box in the way.

Just got finished with this mod.......EPIC!! Works great!!! I didn't get temp readings, but could definitely tell a difference. Still have to clean up and wrap the harness....my white plastic vacuum line was eroded to nothing!! I don't think my blower motor is up to par. Just doesn't seem like it's blowing very hard. I believe it's the original that this Bronco was born with!!
P.S. Note to Autozone....One should have to wait for you to order parts that you should have in stock!!! Vacuum line....REALLY??? Smple vacuum tees.....SERIOUSLY!!!! :-arrgh Maybe it's just me, but if you walk by a shelf, at eye level, and see empty spools where vacuum hose should be, you would order some......that's just me though! :-X15

Cool!!!!!!

And that is why I don't use my local Autozone. My O'reilly's is leaps and bounds ahead of the competitors in town.

We have Advance, Autozone and a private owned NAPA which is the "KING" of "we don't have it, but we can get it in tomorrow!" Otherwise I have to drive about 20 miles to get to the big Napa.

I wear my O'reilly's cap when I shop and always start at O'reilly's. They can get Motorcraft also.