Vechile: 2003 Mazda Truck B3000 2WD 3.0L MFI FFV OHV 6cyl

Whenever I turn on the /AC, the heater hose coming from below the upper manifold near the water pump housing up to the heater control valve in the picture leaks from the fitting before the heater control valve and leaks from the inlet and out let heater core nipples on the firewall above the AC compressor box.

I already installed new hose claps and made sure they were sufficiently tight. I turned the AC heat on full blast and the hose started leaking after about 5 min.

Is it possible that the diaphragm inside the HCV is not closing when the AC is on and is always open and therefore the coolant flowing to the heater core behind the firewall is 'backing up' and leaks when the AC is on? too much pressure? how do I test a HCV?

Also after answering this question, if you want and can, can you please explain to me how turning on the AC while the coolant is still flowing through the heater hoses would cause pressure build up?

I doesn't leak when the AC is off. Sometimes the hose will leak from the inlet heater core nipple a tiny bit.

TIA!




2003 Mazda B3000 Heater Control Valve

 

It's actually a bypass valve. It is supposed to stop flow of hot water through the heater core and just send it back to the engine when the A/C is engaged. When A/C is off, it switches back to allowing hot water to again flow through the heater core and back to engine. I think I got that right. lol
You can also delete it all together like many have done, with no noticeable difference in cooling the cab.

 

The By-pass Valve is only used in MAX AC and OFF

If its leaking replace it

Grey Vacuum hose operates it, connects to port with red arrow

Cold engine
Remove BOTH heater hoses going to the heater core at the by-pass valve end, and at the "prestone" connector
Point one hose down, so water goes to the ground
Hold Garden hose to the end of the other and see what kind of flow you get

Then Reverse hoses, reverse flow thru heater core
This will tell you if core is plugged up
Should have good flow in either direction

Hope its not a clogged core, have to pull the whole dash out to change it
Try to clean it out as best you can

Heater cores have no assigned flow direction, so these 2 hoses should be reversed every year on ANY vehicle, it helps keep core cleaner

 

ty Ron. This is a reference picture, but on mine there's no gray vacuum hose so I think the bypass valve is not activating at all.
I just figured that the bypass valve might have something to do with the heater core hoses leaking when I turn the AC on.
From the info you shared, if the bypass valve is always open since there is no vacuum, it seems like the water/coolant keeps flowing through the heater core even when the hot A/C is on.
I dunno if the A/C compressor being turned on while the coolant/water flows through the heater core creates more pressure in the cooling system. Does the A/C produce it's own heat / cold air?
At first I thought that the A/C compressor when on affects the pressure in the cooling system, and therefore that might be why then heater hoses (especially if a bit loose at the fittings) might leak. Combined pressure.
Dunno if the compressor's pressure is independent of cooling pressure.
Im still learning this stuff. Appreciate any knowledge.

 

Then disconnected heater core hoses at the engine end or couplers, and do the heater core flush

AC systems in vehicles are separate add-ons, an Option, so vehicles can come with AC or without, doesn't effect the rest of the vehicle's systems

Heater system is part of vehicles cooling system, so found on all vehicles
By-pass valves are not required, and in some systems not designed for a by-pass valve, it causes an issue

In a 2003 Ranger/B-series, the TEMP Control **** on the dash controls an electric motor called the Blend Door Actuator, the Blend Door is a vent/panel that directs air coming from the Blower/fan(in engine bay) as it enters the cab's vent system
All Air is directed thru the heater core when HOT is selected, or all air is directed around the heater core when COLD is selected, so between HOT and COLD some air goes thru the heater core, so you can adjust the air temp at the vents, cooler or warmer

Blend Door Actuator motor was a known issue, its above and to the left of Glove box in the cab
If it fails you will have no TEMP control, blend door is stuck at whatever position it was at when motor broke


AC has a part called the Evaporator, its in the Blower/Fan box in engine bay, has 2 metal tubes coming out of the box
Air from the fan blows thru the Evaporator BEFORE going into the cab to the Blend Door
If AC is on then Evaporator cools the air down thats passing thru it, and the cooler air goes into the cab
There is no "temp control" for AC, its either ON or OFF
Blend Door is the only TEMP Control in the vehicle

MAX AC closes the Outside Air vent, so air in the cab is recirculated
If outside air is 90deg, and AC can cool that down 20deg to 70deg, then Cab air will be 70deg, and if you recirculate the 70deg air thru AC again and get 20deg cooler then thats 50deg air out of the vents so MAX cooling, MAX AC

MAX AC also operated a By-pass Valve in engine bay
Heater core itself will be 180deg after engine is warmed up, and it will radiate that heat even if Blend Door is on COLD setting, so stopping flow thru the heater core causes it to cool down and radiate less heat inside the cab, not much of a difference but not 0 either, lol

Test if Blend Door is working, AC OFF
After warm up change TEMP setting, should get HOT and then cooler as you move the **** to COLD
If not then Blend Door Actuator is not working

Heater at 180degF will over power AC at 40degF, middle temp coming out of vent would be 110degF, lol, if blend door is stuck at HOT

 

ty Grampa. Do You know if you can use the heater bypass valve again and 're-adapt' a vacuum line to use it so the bypass valve doesn't stay open on Max AC/ or off? For me coolant / hot water still seems to be flowing through the core even when I have the AC off. Heater hoses are hot to the touch. Are there any benefits to using a vac to the bypass valve? If so, how would you go about installing a grey vacuum line to the heater bypass valve?
TIA.

 

tyvm. This knowledge helps a lot. I have a few questions.

AIR
Does all air come from the outside fan in front of the accessories? I see that the fan is blowing toward a radiator/evaporator like panel (looks like a smaller version of the radiator) in front of the truck. Theres two metals lines coming from the AC compressor that go into this unit. they then branch out to the Blower/Fan Box.

So I understand that air for regular HOT --In Between-- COLD air is coming from this fan through the smaller radiator/evaporator like unit through the metal lines coming from the air compressor into the air box through the evaporator (even though it's off and doesn't have any suction with the AC off) and finally through the blend door and the cabs vents.

From what I understand, The Air compressor turns on when AC or Max AC is on and the evaporator 'turns on' to cool the air and the compressor also helps with cooling the air coming from the fan.

AC
by AC and Max AC being ''on or off" and not having any temp control you mean that the blend door always stays in the cold position when either AC or Max AC is on, right? AC and MAX AC don't produce hot air and the reason why it takes a while for them to produce cold air is because it takes a while for the radiation from the heater core to lower.

Please correct me if I'm wrong of the statement: "AC and MAX AC don't produce hot air" this will help me further verify if my AC is working properly or not.

TIA.

 

No, the Blower/fan is in the "heater box" in engine bay, passenger side, on the firewall(cab)
Picture here: https://www.therangerstation.com/Mag...eatercore4.jpg

Blower>>>>evaporator>>>>Blend Door>>>heater core

The Fresh Air vent is located above the Blower under the Cowl, between hood and windshield, the actual vent opening is hard to see it
In MAX AC a Vent flap is closed and outside air is cut off, the Blower then pulls in air from inside that cab, passenger side just under glove box


The engine cooling fan is near the radiator on the front of the engine, it circulates air in engine bay and pulls air in to cool the radiator when stopped, no connection to cabs Climate control


AC works by compressing a Fluid(R134A) to 200+ PSI
And then releasing the high pressure slowly into the Evaporator, this causes the evaporator to cool down to about 40degF
Compressor cycles on and off to maintain the 200+ PSI, it has a Pressure switch so pressure doesn't get too high or too low, when its ON
When you turn AC off then pressure in the system drops to about 50 PSI

Your refrigerator/freezer and Home AC system works the same way, except it will have a thermostat as well as the pressure switches to cycle compressor on and off as needed
New Vehicles can also use an AUTO TEMP control like a thermostat in a home
But in any setup the compressor is either ON or OFF there is no slower/faster settings, just compressor on or compressor off

AC is very simple, only 1 moving part, the compressor, it takes advantage of the physics of compressing and releasing, compressing cause heat and pressure(stored energy), releasing causes cooling and lower pressure
If you release air pressure from even a hot tire, air will be COLD, is going from high pressure inside the tire to lower pressure outside the tire


No, the Blend Door is controlled only by the **** on the dash(1995 and up)
Settings on other controls do not effect or change it
AC on or off just activates or deactivates compressor

In vehicles with Automatic Climate control, you can set a TEMP and most of these do control the Blend Door, and AC on or off as well