5. Too much gas pressure causing the furnace to overheat because too much heat
is being produced. This causes the furnace to cycle too much on high limit. Does
your furnace’s gas pressure sound like a jet when it is running? Your gas
pressure on your gas valve might be set too high. This produces too many BTU's
or too much heat. I would recommend a HVAC technician adjust this problem.
Turning the adjustment screw clockwise gives more pressure. Counter clockwise
gives less gas pressure. If you attempt to adjust this yourself, do not adjust
more than 1/4 turn clockwise or counter clockwise. Delayed ignition, blow
back, and a mini explosion, could occur. Again, I would recommend an
HVAC technician do this adjustment. Getting this adjustment right will save you gas utility costs,
and wear and tear on your furnace in the long run.
Pressure Switch, Limit, Roll out Switch
or Furnace Control Board Problems?
Problem: My furnace's ignitor does
not glow? This could be a pressure switch, limit, roll out switch, or furnace
control board problem.
I see this problem many times during the heating season here in
Louisville, KY. When your thermostat calls for heat the draft inducer
(please see pictures below) should start which creates a draft in your vent pipe. If your vent piping is
open and your pressure switch is working properly the pressure switch will close
the connection between two wires and send a signal to the control board saying,
"Yes it is OK to continue with the ignition process."
Above
are pictures of a draft inducers showing where the pressure switch tube attaches. Pressure switch tubes sometimes attach on the top
bottom or near the center of the draft inducer. These are just two of hundreds
of different draft inducer designs. Some are metal and some are plastic. Most of the time
draft inducers are plastic on 92% furnaces
& metal on 80% furnaces. Make sure the opening where the pressure switch
tube is attached to the draft inducer is open. Sometimes a small wire can be
used to reestablish the hole. Make sure your water drain on a 92% furnace is
open. If too much water backs up into the draft inducer it will not allow the
pressure switch to close.
Also, all of your
limit controls and other safety devices must be closed (a closed circuit between
the two connections) to allow the furnace ignitor
to glow and start the ignition process. If there is a break down in the pressure
switch or other limit safety controls the furnace, for your safety, will not
proceed with the ignition sequence. The computer chip inside the board says,
Wooooh, something is wrong here! Most furnaces will try this sequence for a
total of three times then lock out. On most furnaces the only way to get them
out of lock out mode is to turn the switch (looks like a light switch) on the
side of the furnace to off and then back on again.
Above
is a picture of three different types of limit controls. The two on the
ends
should reset automatically when the furnace cools down. The rollout
limit
switch in the center has to be manually reset by pressing the button in
on
the top. All limit controls are there for your safety. Never
by-pass these.
How do you test a pressure switch and other limit controls? This
is for people who are experienced with electrical equipment and the use of a
Volt Ohm meter. *Please never by pass a pressure switch or limit control. The
pressure switch and limit switches are there for your safety.
In the top picture I am testing a rollout limit switch to
see if it is good. You would test by setting your volt meter to "Volts AC" and
test the rollout switch by placing one meter probe on one terminal of the
rollout switch and your other meter probe to a good ground. Below I have the red
probe touching the top terminal of the rollout switch and the black probe
touching a ground (body) of the furnace. You can see the I am getting 25.85
volts which means the rollout is good on the top terminal. I would next test the
bottom terminal of the rollout by touching the red meter probe to the bottom
terminal on the rollout switch and the black terminal to ground. If I get 25.85
volts on the bottom terminal the rollout is good. If I do not get any voltage on
the bottom terminal then the rollout has tripped and can be reset (if equipped)
by pressing in on the little button or replaced.
If your rollout switch is tripped you
probably have a stopped up heat exchanger or a leaking heat exchanger. I would
recommend calling in a service technician to find out why the rollout switch
tripped. If you have an open limit control either the furnace has over
heated or the limit has gone bad. Problems that would make a limit open up would
be dirty filters, dirty evaporator coil causing a restriction in the air flow or
a slow blower motor (check the capacitor on the blower motor to make sure it is
good). A weak blower motor capacitor will cause the blower to run slow and
eventually fail. Pressure switches, and limit switches can be tested with a
meter in the same manner. With the furnace calling for heat you can test
each of the terminals on the pressure switch to ground to make sure the pressure
switch is closed. You should be getting between 24 to 28 volts from each
terminal to ground if the pressure switch is closed. If the pressure switch is
open you either have a stopped up vent, drain line (if you have a condensing
furnace) or bad pressure switch. Below
we have three pictures of pressure switches. The picture on the left shows the
full view of one pressure switch. Please keep in mind there are many different
types. The picture on the right shows the two terminals that you can use to test
to see if the pressure switch is operating properly. The front terminal is burnt
and discolored. This is a clue that this pressure switch has a problem. The
picture on the bottom is a black Goodman, Janitrol plastic pressure
switch.
Above pic
shows me testing a rollout switch.
Above
are two pictures of pressure switches. The pressure switch on the left came off
a 92%
furnace.
It has two connections for pressure tubing. One tube would go to the water
collection
box
and the other tube would go to the draft inducer. The switch on the right has a
burnt front terminal.
Above
is a picture of a Janitrol Goodman pressure switch.
How do I test to see if a pressure switch
is operating properly?
Set your meter to volts AC, turn your furnace on so it is
calling for heat. The draft inducer should start. There should be either two or
three wires going into your pressure switch. Probe one lead of the pressure with
one lead of your meter while touching the other lead of your meter to ground.
Ground would be any bare metal part of your furnace. This must be bare metal. I
always try to touch the other lead of my meter to the furnace's switch box. If you have a two wire
pressure switch you should be getting 24 or more volts between both leads to
ground. By this I mean if you touch one terminal of the pressure switch with one
lead of your meter, and touch the other lead of your meter to a ground, bare
metal part of your furnace, you should get 24 or more volts (24 to 28 volts). If
you do not get 24 or more volts with the furnace running then you have a
pressure switch problem. Your vent could be stopped up, The tube that runs from
your pressure switch to the draft inducer could be plugged up or the draft
inducer hole could be plugged up. On high efficiency condensing furnaces the
water drain line could be stopped up, causing a water back up and blockage in
the pressure switch tube. I usually take the drain hose loose from the
condensing furnace and use a wet vacuum to open the drain back up. I hope this
will help you in troubleshooting your gas furnace pressure switch.
Problem: Draft inducer will not start,
ignitor will not glow or gas valve will not open.
Solution: Any combination of the above problem or
problems could be caused by a bad furnace control board. I always troubleshoot
and test the least expensive parts first, such as the pressure switch, limit
switch and rollout switches to make sure they are all closed and operating
correctly before I go to the control board. First, and
most important things to remember is turn your electrical power off to the
furnace. Most control boards are located in the
blower compartment.
Many control boards have a fuse located on them to protect
the board from getting burned up if you have a short to ground. The fuse is
usually a 3 to 5 amp fuse similar to the fuses that you might find in a car's
fuse box. Please see picture below of the furnace control board:
If you fuse is blown you will want to check and see if any of
the low voltage thermostat wires are touching the metal frame of the furnace or
grounding out. Most of the time I see fuses that are blown from animals chewing
through the thermostat wires and from the wires grounding out to the body of the
furnace where the wires enter or exit the furnace. The vibration of the furnace
over time sometimes wears through the wires insulation and causes a short to
ground. I would try a new fuse first, then if the fuse blows again you are going
to need to find out where the wires are shorting out. This can be quiet time
consuming.
If your fuse is OK, tape your door safety switch shut so you
can view the status LED light on the control board with the furnace power on.
Please remember to turn the power back off before touching anything inside the
furnace. I do not want to hear of anyone getting hurt or shocked!
Turn your thermostat up so it is calling for heat. Let the
furnace cycle and see if the Status LED flashes a code. The directions for
reading the code are usually located on the furnace door. The code will usually
tell you what is wrong with the furnace. Technology is amazing! Best of luck on
repairing your furnace. Please remember to turn
that power back off before touching anything.
Troubleshooting Electric Heat
problems:
Problem: Electric heat will not
come on or fan will not come on.
1. First and most important, Please
make sure your electrical power is turned off before trying to repair or inspect
any type of electrical appliance. I would
recommend that you purchase an Volt Ohm meter for some of the troubleshooting
procedures listed in this section. We have a reasonably price Volt, Ohm,
Temperature testing meter on our Favorite HVAC
Supplies & Tools Page.
2. Inspect the inside of the air handler or electric furnace
for burnt wires. I find this to be a major problem. Electric furnaces use lots
of electricity. Any connections that are the least bit loose inside the furnace will cause a
heat build up, arcing and eventually a completely burned off connection. Before long the entire wire will be burnt
off. Please see picture (compliments from one of our nice customers) below of a
burnt heat sequencer. You can see where the heat build up and arcing has caused
the terminals to completely burn off the left side! This looks like a three
stack sequencer, because of the divisions in the layers of the sequencer:
I intend to include a wire repair kit with connectors before
long on our site.
3. Check your breakers or fuses inside the air handler. Again,
make sure your power is off. A good electrical
tester multimeter would be nice to test your fuses. Many air handlers have
fuses in them like the ones pictured below. You can remove these fuses and test
them with a multimeter or if you do not have a multimeter, install new fuses to
make sure they have not gone bad.
4. If you still are not getting electric heat then you should
test your sequencers to make sure they are working. I made myself a tester so I
could get portable 24 volts without having the furnace power turned on by using
an old fan center connected to a junction box with alligator clips attached to
the fan center. We sell new fan centers on our Fan
Blower Controls Page.
Tester
made from Fan Center.
Son's
13 Tennis shoe propping up tester. Ha!
When 24 volts is applied across the two bottom connections on
this sequencer you should get continuity (a closed circuit) between the two
terminals the one on the left M1 and the one on the right M2. You should also
have continuity between M3 & M4. This might take 30 to 90 seconds after the
24 volts is applied before you get the continuity. If you do not get continuity
then you might want to purchase one of the sequencers we have below.
Below are links to some of my favorite sites for Heating, Air Conditioning repair and
advice:
We Sell Heating, Air Conditioning Parts & Supplies To You At Low Wholesale Prices!