"heater head" failure

There are several possible reasons why your blower, vent, defrost, AC, and heater might stop blowing air:

1. Blower Motor Failure: The blower motor is responsible for blowing the air through the vents. If the blower motor fails, you will not get any airflow from the vents.
2. Blower Motor Resistor Failure: The blower motor resistor controls the speed of the blower motor. If the resistor fails, the blower motor may stop working or only work at one speed.
3. Fuse or Relay Failure: A blown fuse or faulty relay in the blower motor circuit can prevent the blower motor from working.
4. Control Module Failure: The HVAC (heating, ventilation, and air conditioning) control module is responsible for controlling the blower motor and other components. If the control module fails, it can prevent the blower motor from working.
5. Vacuum Leak: If your vehicle uses a vacuum system to control the vents, a vacuum leak can prevent the system from working properly.
6. Broken Blend Door: The blend door controls the direction of the airflow. If the blend door breaks or gets stuck, the air may not flow through the correct vents.
7. Wiring or Connector Issues: Faulty wiring or connectors in the blower motor circuit can prevent the blower motor from working.

Many vehicles that have both front and rear A/C systems utilize two blower motors; one for the front vents and one for the rear vents. Each blower motor also likely has its own dedicated blower motor resistor to enable independent airflow control. The most common failure items in blower motor circuits are the blower motor and resistor. When a blower motor fails it will not work on any speed setting. Blower motor resistors however, tend to maintain proper operation on HIGH speed but none of the lower speeds; this is not always the case though. Proper diagnosis begins with checking for power at the blower motor. If power is present, the blower motor has likely failed. If no power is present, the blower motor resistor should be checked for power. If power input is present but no output, the resistor has failed. If there is no power input, the fuse should be checked as either one of the component failures could have caused it to blow. After replacing the fuse the same checks should be made again to determine where the power flow stops and why. You can read more here: https://www.yourmechanic.com/article/symptoms-of-a-bad-or-failing-heater-blower-motor-resistor

94 CHEVY Silverado ????,heat/ac fan not blowing. K1500?????? Hear clicking when selecting l'm, SET high but not blowing! WITH AIR OR NO A/C? FIRST IS FUSES, MAKE SURE THE BLOWER FUSE IS NOT BLOWN.
EASY NO? CHECK ALL FUSES FIRST. ON ALL ELECTRICS FAILING OF ANY KIND.
BAD FUSE, BAD WIRINIG , BAD CONNECTIONS. OR EVEN BAD RELAYS TO THE BLOWER OR BAD SWITCH BLOW.
THE OLD CARS , HAD A SPEED BLOW , RESISTOR BLOCK
THAT FAILS ON ALL SPEEDS BUT HIGH, SO ITS NOT THAT.
OWN A VOLT METER????
HERE IT IS, ANY OF THIS CAN FAIL THIS OLD
WE USES A VOLTMETER TO FIND THE POINT OF FAILURE.
A SHORTED BLOWER MOTOR CAN BLOW LEFT SIDE TOP
FUSABLE LINK.RIGHT FUSE BLOWN MAKES THE CONTROLLER DEAD.

Air temperature and delivery are controlled via small actuators on the heating, ventilation & air conditioning (HVAC) box located behind the dashboard. These actuators operate doors inside the HVAC box in order to channel air through different passages to achieve the desired result. A "blend" door actuator can channel air through the heater core, around the heater core or a mix of these two to achieve the desired temperature. A "mode" door actuator can direct airflow to the ducts that lead to the defrost vent, front vent, floor vent or a mix between. When a vehicle has dual climate control (where driver and passenger sides of the vehicle can have different air temperatures) there can be multiple of actuators of each type which can make diagnosis difficult. The first step would be to retrieve diagnostic trouble codes (DTCs) from the HVAC Control Module using an advanced level scan tool; these codes help determine the location of the issue and if it's an electronic or mechanical failure. Electronic failures would include items such as HVAC control module failure, actuator circuit failure or actuator failure. Mechanical failures would include items such as actuator failure or internal HVAC box door failure. You can read more here: https://www.yourmechanic.com/article/what-components-of-the-heating-and-ac-system-are-most-likely-to-fail

so find out which vent is dead,?
before 5 gallon LYSOL flush an a week long GAG !
make sure first never to use RECRIC, when wanting to defog.
and is the A/C running in dash defrost mode (compressor main shaft spins)

if a vent is dead, its a bad damper valve, (not saying a part, a function)
the book is free, you can read it, HVAC. see venting and dampers.
its very simple in concept, a fan, a damper and dry air. hot.
the heater core makes heat the non recirc, damage gives you fresh air, the A/C makes that air dry. and the dampers the supply all vents work work.
so make sure the controls are set right,
then see if the upper vents all blow, with hand waved on them.
see? that is easy, and not reporting a dead vent ,makes help harder.
the FSM is on line, ill look for you.
but first HVAC 101

1. does blower work on high?
2. does the recirc turn to fresh are,and you get fresh air with blower off moving, at all top vents. y/n
3. do you have full heat? 180F + engine heat (scan tool shows this as ECT)
4. do all vents top work , blower on?
5. is the A/C compressor working in A/c mode (cold) and Defrost?
6. more... below.

Rule one, dont work in dash until air bags are DEFEATED (injury) (pull battery neg lug, and wait 1hour)

got fsm page open, ill state some facts needed to fix this.

first ill prove the dash system does not need total dismantle
for all jobs. Does NOT.
Air /mix blend door
Single Zone/Dual Zone Driver's Side(FSM)

1. Disconnect and isolate the negative battery cable.
2. Remove the instrument panel silencer from the driver side of the instrument panel.
3. Remove the three screws that secure the blend door actuator to the driver side of the HVAC air distribution housing .
4. Remove the blend door actuator from the air distribution housing and disconnect the HVAC wire harness connector from the actuator.
5. Remove the blend door actuator from the vehicle.

next page, is blend door 2, type.
has vacuum servos.
we move the controls and make sure all servo vacuum motors
work

this car has driver side and passenger side seperate blend doors.
so,,, we are getting close here>
?
if the defroster fails,(seems not) then that is electric motor drive
and very hard to test . (if not door jam)

in any case, we need to know what part is failing,
if the passenger blend is dead.
seen below,
we then must find out why
1: just stuck.
2: servo actuator failure
3: controls to #2 above bad, or connections to each.



login to alldata.com see HVAC chapter, read how it works and the tests.

I assume your heater setting is electric control, if so either your defrost and floor heat switch failed or wire problem. For the air not hot, check the heat control valve on the top of the hose it should be in front of the firewall. I don't know your car is using mechanic valve or electric control valve. Anyway check there first. Good luck.

Hello from cold Kentucky.
The system uses a fan switch, resistor, and probably a high blower relay.
In the high position, the switch powers a relay that powers the blower motor. Any lower speed goes thru the resistor.
The resistor is on the firewall or under the dash depending on if the truck has air cond.
You can look up a blower resistor on the auto parts websites to get a visual.

you probably have a vacuum leak from the engine or vacuum storage canister to the heater/a/c control head. Defrost is default mode required by law when system fails.

replace the a/c blower motor resister. If it fails again, you will have to replace blower motor.

For the air blowing out defrost (failure mode), you probably have the vacuum harness on the back of the control head not fitting tightly, causing a vacuum leak. Use tie straps to hold it tight.

I have a picture but it's 2.3 mb. Can't post here.

email address is needed to send to you.

If I remember correctly the mode door is vacuum operated. Check to make sure that there is vacuum to the control head. If not is is possible you knocked the vacuum line off when replacing the heater core. The default position for a vacuum controlled mode door on just about every vehicle is the defrost position. This is so if there is a failure in the system you will at least still have a clear windshield to see through.

I’m happy to assist further over the phone at https://www.6ya.com/expert/jeremy_d728a59f986299fa