• Register Today It's free! This box and some ads will disappear once registered!

1991 Ford Explorer Heater Bypass Valve Installation

shamaal

Explorer Addict
Joined
April 25, 2005
Messages
1,248
Reaction score
5
City, State
Friensdwood, Texas
Year, Model & Trim Level
91 Mazda Navajo
I thought of this several years ago and a recent post showed it could be done. On the 91 & 92 Mazda Navajos, there is no shutoff on the heaters. This means the A/C must overcome heat from the heater core in addition to the cabin air. On the newer models Ford installed a vacuum operated heater bypass valve that prevents engine water from going to the heater core core when the A/C environment control is placed in MAX A/C.

MAX A/C also closes the vacuum motor driven RECIRC damper located behind the glove box. The idea will be to take the RECIRC line, add a Tee and route the Tee'd vacuum line to a new heater control valve installed in the engine compartment.

Measured at the vent I gain 10 degrees temp difference between MAX A/C on and MAX A/C off. Incredible!

This photo shows the Heater Control Valve for a 94 Explorer that I bought from O'Reilly (#74809), Autozone does not carry it. The Yellow lines are supply from and return to the engine. The green lines are supply to and return from the heater. As one expects when no vacuum is present the plunger is out (circled) and hot water flows from the top of the engine, into the yellow supply, out the green to the heater supply, through the heater and returns out the green to the valve, through the valve and out the yellow to the return heater hose at the bottom of the block. When there is a vaccum applied the plunger closes and the hot water loops yellow to yellow and the heater loops green to green.
32.JPG


Before cutting up the heater hoses I located the vacuum control line, this is accessed behind the passenger side kick panel, removal of the round plastic rivet that holds it in permits it to be bent out. Note the PCM location. Removal of the heater cover just above this may aid in access but it wasn't necessary. Use caution it's plastic and only bends so far. There's probably a correct way to do this but the rainclouds are gathering.

51.JPG


The object of our interest is the white line going to the vacuum motor shown below, it just slips off. There is also a black line running through the area, that's the vacuum supply coming from the reservoir in the engine compartment leave it alone.

heater1.JPG


With that disconnected I used a 1/8" X 1/8" X 3/16" Tee to tap the control line (Autozone Assortment #47328). The 3/16" white line went to the center, I added a piece of 1/8" hose that went between the Tee and the vacuum motor then ran 4 foot of 1/8" hose (Autozone #65113) through a hole I drilled in the firewall into the engine compartment.

91.JPG


I'm loathe to drill holes in firewalls, but the normal grommet pass through, blurred black object in pic) was filled with black caulk and I didn't feel like dealing with it.

42.JPG


The new control line was picked up by laying down under the car and bending forward the wheelwell cover enough to get my hand in. The fastidious may want to remove the cover and have access to the grommet and do the job right.

71.JPG


Confident I had the control line routed, the next step was to cut the heater hoses and install the control valve as identified in the first picture

102.JPG


The next picture shows the valve all installed. The right top hose comes from the top of the engine (supply) and the right bottom hose goes to the bottom of the engine. The next time I change heater hoses, I'll move the valve closer to the firewall, I think it sticks out to far now. Note that the vent control is in MAX A/C and the plunger is depressed. Compare with the first pic.

111.JPG


As I said earlier, switching MAX A/C in and out causes 10 degree temp swing when measured at the outlet. I wouldn't have thought the design was that bad. Incidentally , even when MAX A/C is selected the heater top hose gets hot while the bottom hose remains cool. I imagine there is some leakthough, but the A/C overcomes it.
 


Join the Elite Explorers for $20 per year. Gets rid of the ads! New $5 per month "try out" option.

Explorer Forum has probably saved you that much already, and will continue to save you money as you learn how to diagnose fix problems yourself and learn which modifications work without having to experiment on your own. Elite Explorer members see no advertisements, no banner ads, no double underlined links, can add their own profile photo, upload photo attachments in all forums, and Media Gallery, create and save more private Conversations, and more. Join Today. Your support is greatly appreciated.




Turdle

Lowrider
Staff member
Moderator
Elite Explorer
Joined
June 16, 2003
Messages
29,586
Reaction score
1,117
City, State
Humboldt, KS
Year, Model & Trim Level
2000 Mounty
You are a great thinker--
Good Idea!! I understand, and believe how it would work without seeing for myself--:thumbsup:
 




DeRocha

NEX Vice President
Elite Explorer
Moderator Emeritus
Joined
July 5, 2003
Messages
6,670
Reaction score
35
City, State
Brockton, MA
Year, Model & Trim Level
'93 XLT 4x4
Very nice mod and right up... :thumbsup:
 




msmith65

Well-Known Member
Joined
August 18, 2004
Messages
349
Reaction score
0
City, State
Dallas
Year, Model & Trim Level
'93 XLT
Nice work! Thank you for pioneering this, and for documenting it for all to see.

I failed to check this forum before starting and documenting my own valve-installation project at the end of this thread.

I used a hard, plastic line and was able to push through the grommet (rather than drill a hole), but it wasn't easy.
 




X-North

Well-Known Member
Joined
July 16, 2007
Messages
552
Reaction score
0
City, State
Montreal
My A/C dont work so im just gonna put a manual valve in the inlet.i will open the hood nd switch the valve on and off so it gonna stop like that...i wont put much on a 205000 kms rotten truck that i paid 750$ :D
 




rsoby

New Member
Joined
May 23, 2010
Messages
5
Reaction score
0
City, State
Cape Cod, Ma.
Year, Model & Trim Level
'94 XLT
Can you think of any reason this mod could not be installed in such a way as to use a vacuum control valve inside the vehicle so that you could turn the heater core on and off at will. I have a 94 Ex and when you slide the temp control to cool and it allegedly shuts the door bypassing the heater core the heat is still pretty strong coming out. It would be nice to be able to shut it down and get cool air through the vents on days that AC isnt neccessary.
 




josh000888

New Member
Joined
May 11, 2010
Messages
9
Reaction score
0
City, State
va beach, VA
Year, Model & Trim Level
91 Explorer XLT 4x4 4 dr
I found a valve in a 94 EXP at the junk yard on Saturday and picked it up after reading your article. Then stopped off at NAPA, and it appears their 21.00 valve didn't work as good as my 3 dollar junk yard piece of art. Thanks Shamaal! I had definite bleed through to the point of only getting 54 degree air through. Was going to put it on this evening, but my son came home and said no air is coming out of the vents Dad...How come? Could it be the dreaded plentym box door I've been reading about, or is their something else?
 




96AWD5.LOL

Active Member
Joined
March 14, 2012
Messages
50
Reaction score
12
Location
Austin, TX
City, State
Austin, TX
Year, Model & Trim Level
91 XLT 4x4 - Red Velvet
Ancient thread, but useful...

For those who have done this mod can someone verify for me that the top hose on the right side of this picture goes to the top of the engine by the thermostat and that the lower right hose goes to the water pump location? I'm asking because I did this mod this past weekend to improve vent temperatures and I've actually seen the reverse happen, it got warmer. The plunger moves, vacuum is working on the valve.. The top left hose is cool. The bottom left hose, which I thought was the heater core's "out" line, gets hot?

111.JPG
 




Maniak

Moderator-Stock 91-94
Elite Explorer
Moderator Emeritus
Joined
February 9, 1999
Messages
12,095
Reaction score
116
City, State
Vail, Arizona
Year, Model & Trim Level
1992 XLT 4x4
Ancient thread, but useful...

For those who have done this mod can someone verify for me that the top hose on the right side of this picture goes to the top of the engine by the thermostat and that the lower right hose goes to the water pump location? I'm asking because I did this mod this past weekend to improve vent temperatures and I've actually seen the reverse happen, it got warmer. The plunger moves, vacuum is working on the valve.. The top left hose is cool. The bottom left hose, which I thought was the heater core's "out" line, gets hot?

111.JPG

The Coolant direction is out the head to the heater core and then back to the water pump. the heater control bypass valve should have arrows molded into it so you can make sure the coolant is going the right direction. So, it your picture, the top hose should be coming from the head and the bottom hose (still on the right side) goes to the water pump.

~Mark
 




Top