[Unknown User]

I have a problem of no heated air coming out of my automatic temp.
system (when set to fully hot). I've recently replaced the heater
control valve/****, and it didn't make a difference.

The a/c works still and the air gets redirected properly when I go to
defrost and hot, it's just that the air is no longer heated. I also
think I felt the heater hoses in the engine compartment and they
were also hot.

Does anyone have any ideas of what else I could look for. I've heard
of inspecting the air-mix door and even backflushing the heater
core, but I'm not too familiar with those areas.

 

[Bob A]

I am certainly not an expert on the Heater/AC unit but as I recall there are only two things that can cause you to have no hot air.

The first is that you aren't getting air through the heater core. If this is the case it's most likely caused by the air mix door. This door is independent of the defroster or vent doors and proportions the hot and cold air by changing position from full cold to full hot or somewhere in between. A vacuum servo provides the power. As I remember, you have to have vacuum to it to move it to the heated air position. No vacuum will move it all the way to the cold air position.

The second thing is you have to have water flowing through the heater core. The water valve/**** turns flow off and on. Since you replaced it, the only other thing to keep water from circulating is if the hoses, lines, or core is plugged. I don't think that's the case because you say the lines are hot. Are they engine temp hot? If so then you have water circulating and the problem is probably vacuum to the air mix door servo.

The Haynes manual I have does not go into any detail on the auto AC/Heat. I also have a Popular Mechanics CD that I can access repair info on and it's got a lot but still probably not enough. That disk is available at www.alldata.com for around $30.

Hope this helps.

Bob A
IZCC #5497
83 280ZX N/A

>I have a problem of no heated air coming out
> of my automatic temp.
> system (when set to fully hot). I've
> recently replaced the heater
> control valve/****, and it didn't make a
> difference.

> The a/c works still and the air gets
> redirected properly when I go to
> defrost and hot, it's just that the air is
> no longer heated. I also
> think I felt the heater hoses in the engine
> compartment and they
> were also hot.

> Does anyone have any ideas of what else I
> could look for. I've heard
> of inspecting the air-mix door
> and even backflushing the heater
> core, but I'm not too familiar with those
> areas.

 

[Unknown User]

I've determined that the following are OK:

- Heater hoses
- Vacuum hoses (all of them)
- Heater valve/**** (which was replaced)

The only thing I can think of is the source of the vacuum, something called the actuator (or servor). If this part went bad as I suspect it did, then I'm looking at just replacing that or the entire control unit.

 

[Bob A]

Like I said I'm not an expert. So I consulted my Haynes manual.

If your air mix door is in the full cold position you will get no hot air out of the heater. This is independent of the other doors that direct the air to the defroster etc.

In order to get the air mix door to move from the full cold position there must be vacuum applied to the power servo. This vacuum is directed to the power servo from a device called the transducer which takes an electrical signal from the temperature control amplifier and converts it into a vacuum signal.

So.... the vacuum is provided by a line from the intake manifold that runs to a vacuum tank on the right fender well and then in to the passenger compartment. It spits off to the transducer, a mode vacuum selector and a temperature vacuum selector. From the transducer it goes to something called the vacuum lock valve (which blocks the vacuum signal during momentary vacuum drops) and then to the power servo.

There are several electrical devices that tie in to the temperature control amplifier. They are called the ambient temperature sensor (located behind the front bumper), the In-car sensor (located in the dash), the feedback reostat (connected to the air mix door), And the temperature control reostat (I think that's the knob that you slide back and forth for the different temperatures). Anyway the temp control amp takes the resistance from all these devices and send a signal to the transducer which then varies the amount of vacuum applied to the power servo and therfore varies the position of the door.

So... while i really can't tell you any more than this, it is my opinion that just about any of the previously mentioned components could be causing the air mix door to remain in the full cold position.

Hope this helps.

Bob A.

> I've determined that the following are OK:

> - Heater hoses
> - Vacuum hoses (all of them)
> - Heater valve/**** (which was replaced)

> The only thing I can think of is the source
> of the vacuum, something called the actuator
> (or servor). If this part went bad as I
> suspect it did, then I'm looking at just
> replacing that or the entire control unit.