Pressure Switch on Luxaire Furnarch
throwa...@gmail.com
that the pressure switch is stuck open (2 flashes) - this is probably
because the fan with the pressure tube does not start. If I bypass the
control and run the motor straight from power, the switch now reports
stuck closed (which makes sense). If i pull the tube off and put it on
quickly the furnace will start no problem.
When I first looked at it, the switch wouldn't switch at all - I had
to clear out the tube going into the fan housing. Logic is telling me
that the issue is the control unit which isn't starting the fan, which
makes the sensor report stuck open - correct?
PS I did take the pressure switch off and test it - it works fine.
Before I go out and but the control unit I was just looking for a
second opinion.
Thanks!
Joe
>snip<
> PS I did take the pressure switch off and test it - it works fine.
Pressure switches operate at very low pressures. If your test was a
brute force one like blowing into the small tube and checking
continuity, the test could be meaningless. Before buying a pricey
control board, it would be interesting to see if a new pressure switch
and related tubing would solve the problem. Good luck.
Joe
throwa...@gmail.com
Thanks Joe, while it is true that the test was 'brute' force,
shouldn't the motor switch on first? otherwise there would never be a
vacuum ????
The Daring Dufas
air to clear them, sometimes a piece of wire is needed
too. If you removed the switch, make sure you reconnect
the correct terminals. If it's like many of them, it has
a common (C) a normally open (O) and a normally closed (N).
This is the type that has a microswitch on the back and
looks like this example which has only two terminals:
http://www.johnstonesupply.com/catimages/4557.jpg
There could be some debris in the switch also. Sometimes
whacking with a screwdriver handle can knock it loose
and get it back into operation, often permanently.
I would check all the safeties because control boards
can be quite expensive.
TDD
throwa...@gmail.com
The switch is just like that. I did actually have to clean out the
connection and tube to even make it work, so I'm pretty sure that the
switch is working as the furnace does at least run now after I 'faked'
it out.
Should the motor run before turn on before it does a status check on
the switch?
The Daring Dufas
If you can fake it out, it's not the control board.
There could still be debris or a partial blockage in
the metal line. You can take a piece of stranded wire
and strip about inch of insulation off, fray the wires
into a sort of brush and run it in and out of the metal
tube. Those pressure switches are very sensitive and
any restriction in the draft inducer blower or exhaust
from the furnace could keep things from running. The
way most furnaces of your type work is:
1: The thermostat calls for heat by sending 24 volts AC
down the white wire to terminal "W" on the control board.
2: The draft inducer blower starts running and the motor
has a switch that tells the control board that the motor
is turning.
3: The control board expects a signal from the pressure
switch within a few seconds.
4: If the control board gets a proper signal from the
pressure switch, the igniter comes on, I assume it's a
hot surface igniter. You can tell by the bright orange
glow in amongst the burners.
5: The electric gas valve opens feeding gas to the burners.
6: If the burners ignite, a flame sensor probe signals
the control board that there is a flame.
7: After a few minutes, the heat exchanger gets hot enough
to trip a sensor that tells the control board to turn on the
air handler blower.
Nothing will work if things are out of sequence or no signal
is received when expected by the control board's program.
There are several over temperature sensors and one or more
"anti roll out sensors" which detect if the flame rolls out
backward into the furnace. The safety sensors and anti roll
out switches usually have a little manual reset button between
the electrical terminals. Your furnace may vary slightly from
my description, a spark igniter instead of a hot surface type
for instance but most standard modern 80-90% efficiency gas
furnaces work this way. This is not a complete explanation of
the inner workings of the furnace but it may help you understand
it better.
TDD
Tony Hwang
Pressure switch is of differenbtial type. Never bow into it.
If incuder motor turns normal and there is no obstruction in the tube,
maybe the swtch is a toast.
Tony Hwang
That switch is differential type pneumatic switch. If you blow into it,
it'll be damaged, If inducer motor spins normal and there is no dirt
inside the tubing, the switch assembly is a toast.
Don Young
<throwa...@gmail.com> wrote in message
news:0c5f40e5-2eeb-4d87...@l76g2000hse.googlegroups.com...
At least some of the controls check the status of the switch(es) before
starting the fan. If the status is correct, the fan is started and the
status of the switch(es) is monitored for a status change. This is an
additional safety in case the switch is stuck or bypassed.
Don Young
The Daring Dufas
state for the switch to be in until after the draft inducer
has had time to spin up and activate the pressure switch.
Anything that's out of sequence will cause a shut down and
or lockout. Often a lockout can be reset by turning the power
or thermostat off then back on.
TDD
ransley
> Clean out the tubes, port or condensate lines
> Replace the inducer motor
> Replace the control board
> Replace the Heat exchanger
> Prob a few other possibilities too.
> Depends on how much time and money you want to waste.
> Bubba- Hide quoted text -
>
> - Show quoted text -
And this hack advise is from a guy that knows from on job learning, no
schooling of course.
throwa...@gmail.com
*** So, based I'm deducing that the control is history as the
thermostat does close the circuit (triggers), but the draft inducer
does not start. I'll check the wires as a final option, but I feel now
that I'm in denial about the unit. Thanks everyone for the input.
The Daring Dufas
involved in the various functions. Since I've never seen
your furnace, I can only generalize. I repair equipment
all the time that I've never seen before but I know who
to ask. I helped a friend work on a new HVAC unit that I
had no experience with and we thought something was wrong.
After a quick call to the factory rep our questions were
cleared up and what we thought was a malfunction was, to
my surprise, normal operation.
TDD
Don Young
<throwa...@gmail.com> wrote in message
news:595cd9cf-e101-48f2...@b31g2000prb.googlegroups.com...
You have not verified that the control is bad unless you have verified that
the pressure switches are in the correct state for start-up (probably open)
and the control has been reset. Also verify that your AC wiring is correct
as some controls will not work if the ground is missing or if the hot and
neutral lines are reversed.
Don Young
ransley
> On Fri, 31 Oct 2008 05:10:18 -0700 (PDT), ransley
> You on the other hand ransley are a complete and udder fuckwit. One
> merely has to google search your posts to figure that out.
> Sucks to be stupid like you, ransley, eh?
> Bubba- Hide quoted text -
>
> - Show quoted text -
Is there ever a post or customer, or person you dont use profane
insults with. You must be a sucessfull business person, HAAAAAAAA
hAAAAAAAA Haaaaaaa.....
ransley
> On Fri, 31 Oct 2008 05:10:18 -0700 (PDT), ransley
>
>
>
>
>
> <Mark_Rans...@yahoo.com> wrote:
> You on the other hand ransley are a complete and udder fuckwit. One
> merely has to google search your posts to figure that out.
> Sucks to be stupid like you, ransley, eh?
>
> - Show quoted text -
So post em moron, you are the guy that said 20 years is needed to
learn to do Your job, So I say you just hacked your way through 19 yrs
11 months 3 weeks of unhappy customers. Our local tech college teaches
you with Pros, not hacks. But geese im no Hvac person, but I can sure
spot a loudmouth dumb ass crook.
Baldy
out the blower and found out that air was leaking around the gasket. I
removed some of the spacers from under the fan and tightened it down and
the vacuum switch functions normally now.
--