How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Phil Your Own Question
Phil
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 8511
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
23932409
Type Your HVAC Question Here...
Phil is online now
A new question is answered every 9 seconds

Goodman GDS not lighting. Light blinks 4 times. Just

Customer Question

Goodman GDS not lighting. Light blinks 4 times. Just installed new high limit switch. Still not lighting... Any ideas?
Submitted: 1 year ago.
Category: HVAC
Expert:  Tim H. replied 1 year ago.

Hi, I'm Tim and I'm an HVAC expert here to assist you with your questions. Please provide all information I request as it makes it more difficult to troubleshoot something when I'm not there onsite. Essentially, you become my eyes and ears. Thanks for the opportunity to help. At the end of our dialog, you will have a chance to rate my service, but please wait until we are finished and you're satisfied you have all the information you need.

Is the blower working?

Customer: replied 1 year ago.
The blower and another fan both run and seem to change speed.
Expert:  Tim H. replied 1 year ago.

The 4 flash code refers to an open pri***** *****mit switch. This can be caused by insufficient airflow through the furnace as well as a bad limit switch. It can also be caused by defective wiring to and from the limit switch.

Customer: replied 1 year ago.
When you raise the temp on thermostat to make heat come on the blower starts right away. But it doesn't light...
Expert:  Tim H. replied 1 year ago.

It won't light as long as the board sees an open limit.

Customer: replied 1 year ago.
What needs to be checked?
Expert:  Tim H. replied 1 year ago.

As i mentioned, first make sure blower is working. You could have a plugged filter or plugged A-coil (for the air conditioning). Finally the wiring could be bad from the board to the limit.

Customer: replied 1 year ago.
Are there tests you know I should perform?
Expert:  Tim H. replied 1 year ago.

See below:

Customer: replied 1 year ago.
Where is the pri***** *****mit switch? This happened during/after wind storm... How can the pri***** *****mit switch be tested?
Expert:  Tim H. replied 1 year ago.

In other words, it is not just a faulty pri***** *****mit that can cause this code.

Expert:  Tim H. replied 1 year ago.

I thought you said you had already replaced the high limit??

Customer: replied 1 year ago.
What's a primary A coil? Located where? The wiring looks good. Yes I replaced Upper limit switch (same thing?) with OEM part.
Expert:  Tim H. replied 1 year ago.

A-coil is the part on top of your furnace connected to your air conditioning.

Customer: replied 1 year ago.
Are there other filters to check/service besides the normal house filter in the ceiling?
Expert:  Tim H. replied 1 year ago.

Shouldn't be, no.

Customer: replied 1 year ago.
Wiring looks ok, filter was dirty but you could see through it still... New limit switch... Sounds like I need to look at A coil. What do I look for?
Expert:  Tim H. replied 1 year ago.

Plugged fins.

Customer: replied 1 year ago.
No other tests or something to jump to bypass to test? If the fins are dirty and I clean them the furnace will work again?
Customer: replied 1 year ago.
What is preventing the gas and igniter to operate?
Expert:  Tim H. replied 1 year ago.

Start with the simple stuff. Put a new furnace filter in. Turn your thermostat fan to ON position. Is air flowing good out of the house vents?

Expert:  Tim H. replied 1 year ago.

If not, you may need to have your A-coil cleaned. Any place that does duct cleaning should be able to clean A-coil.

Customer: replied 1 year ago.
Yep... Did that first. Then turned off breaker and tried restarting with no call for heat. Then raised thermostat... Blower comes on ut no heat
Expert:  Tim H. replied 1 year ago.

As I said previously, the burners will not ignite as long as the board is seeing an open limit switch.

Customer: replied 1 year ago.
What is holding the limit switch open?
Expert:  Tim H. replied 1 year ago.

Plugged A-coil, dirty filter, blower not working or running slow.

Customer: replied 1 year ago.
electrically speaking what switch or sensor is holding the limit switch open?
Expert:  Tim H. replied 1 year ago.

There is no switch or sensor holding it open. It is there to keep furnace from overheating. Things mentioned previously will keep it open.

Customer: replied 1 year ago.
Your story doesn't add up electrically. I make wire harnesses for Diesel engines. Something must be interrupting the circuit allowing the igniter and gas to operate.
Expert:  Tim H. replied 1 year ago.

The limit switch is a switch designed to open (electrically) when furnace gets too hot. At the same time, it shuts off burner because if we are getting poor airflow through the furnace (caused by the things I previously mentioned--plugged furnace filter, blower not working or running slow, or a plugged A-coil), we do not wnat the burner on. It is designed to open and shut off burner in the event of any of these things.

Customer: replied 1 year ago.
How does the board know the A coil is plugged? How does the board know the airflow is insufficient?
Expert:  Tim H. replied 1 year ago.

Switch has a temperature rating designed to open above that temp.

Customer: replied 1 year ago.
The blower is working normal. Lots of air out of the registers
BTW the limit switch is cold... No hot air. But lots of air flow
Customer: replied 1 year ago.
How could limit switch be keeping system from lighting?
Expert:  Tim H. replied 1 year ago.

Then I would check the wiring. It may look OK, but if anywhere along the line of the wiring between the limit switch and the board it is a poor connection, the board would see that as an open limit.

Customer: replied 1 year ago.
I'm sorry to say you have been of little help. Other than checking wires and cleaning you haven't offered any tests to confirm or trouble shoot the circuits responsible for operation.
Expert:  Tim H. replied 1 year ago.

I have tried to explain to you the things that cause an open limit. I have alos explained why, with an open limit, furnace will not light. I'm not sure what else I can do. I suggest checking the things I mentioned if you've already replaced the limit switch itself.

Customer: replied 1 year ago.
I'm not satisfied... I'm no farther along than I was before I contacted you. How do you test the limit switch? Maybe we shouldn't assume the new switch works?
Expert:  Phil replied 1 year ago.

Hello, if you have the patience to continue I can help I believe.

If that is the case please attach a well focused, close up photo of the wiring diagram glued inside the service panel, the picture needs to be taken from straight on, in very good light.

You can use the paper clip- icon at the right end of the tool bar at the top of this dialog box to attach it here.,Include a picture of the thermostat wire connections to the printed circuit board in the same area.

If you have an error code showing, tell me what the code read out is on the wiring diagram or a sticker next to the diagram please.

If there is no paper clip-icon, look for the '+attach files'link at left of your send button.

I can mark it up with trouble shooting instructions.

Its late here, I will pick up your response in the morning, or you can opt me out if need immediate assistance. Other of our experts might be up this late, its a long shot though.