Mechanics

NO HEAT FROM HEATER

1998 Mazda b2500 • 100,000 miles

I've opened the heater water valve and the hoses to and from the valve get hot but no heat inside. The truck has A/C.
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Tom@andersonacres.com
December 27, 2011.



Check to see if the blend doors in the heater box open and close properly.


Rivermikerat
Dec 27, 2011.
How do I do that?


Watch the actuators and listen for the doors moving. With the engine running.


Rivermikerat
Dec 27, 2011.
I've removed the glove box and have access to some of the heater a/c actuators. The air is directed to foot, vents and defroster properly but always remains cold irregardless of the temp **** setting. Is there a blend door that would effect whether the air is passed through the heater core as opposed to an ambient sourse? Where is this door located?


A/C-HEATER SYSTEM -1998 Mazda B2500 SE
Page 1 of 1
TEST NO 2: INSUFFICIENT, ERRATIC OR NO HEAT

1.
Inspect cooling system. Check and fill coolant level, pressure test system and radiator cap. Ensure water pump and belt are okay. Repair or replace as necessary. Start engine and bring to normal
operating temperature. If cooling system is okay, go to next step.
WARNING: Heater core hoses may become extremely hot. When checking these hoses, caution should taken to avoid personal injury.
2.
Select heat mode and place temperature control to maximum hot setting. Feel heater control valve inlet and outlet hoses. If inlet hose is hot and outlet hose is warm or hot, go to next step. If inlet
hose is hot or warm and outlet remains cold, go to step 5). If both hoses remain cold, check cooling system.
Start engine. Select any mode other than MAX A/C position or OFF position. Disconnect and check for vacuum supply to heater control valve. If vacuum is present at heater control valve
vacuum hose, go to next step. If vacuum is not present, check vacuum circuit. See TEST NO 1. 4. Using a vacuum pump, test operation of heater control valve. While observing actuator rod of
heater control valve, apply vacuum to actuator. If actuator rod does not move or does not hold vacuum, replace defective heater control valve. If heater control valve rod operates and holds
vacuum, go to next step.
Remove heater control valve and check for plugged or restricted heater core. If core is restricted o
plugged, replace heater core. See A/C-HEATER CASE ASSEMBLY under REMOVAL & INSTALLATION. If heater core is okay, repair blend air door as necessary.
3.
R

5.

Also see image for blend door actuator connector layout.


Rivermikerat
Dec 28, 2011.