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.
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.
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.
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.
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.
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.
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
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.
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.
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.
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.
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.
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.
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.
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.
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
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.
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.
