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: 6022
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

I have tried replacing the thermal limit switch and I am

Customer Question

I have tried replacing the thermal limit switch and I am still getting the 4 blink error code. HELP
Submitted: 1 year ago.
Category: HVAC
Expert:  Rick replied 1 year ago.

Welcome to Just Answer, my name is ***** ***** I will do my best to help you with your issue. First I’ll need some more info so I have a more complete picture of you situation.

The rollout switch(es) (see attache pic) are also in the limit circuit. You can try resetting them by pushing the small button between the 2 wires. If it clicks you have reset it. If it doesn't click it wasn't tripped. They are located just outside the burner chamber.

Customer: replied 1 year ago.
This is a Trane XR80
Expert:  Rick replied 1 year ago.

The same answer still applies

Customer: replied 1 year ago.
I can call you on my cell so I can show you what I see
Expert:  Rick replied 1 year ago.

A phone call is an additional cost. Let me know if you want to talk and I'll post an additional service offer. Or we can continue here. You can post pics here by clicking on ADD FILES next to the SEND button

Customer: replied 1 year ago.
I don't see any button like the one you showed. Would it be behind what looks like a breaker box inside the furnace compartment
Expert:  Rick replied 1 year ago.

It will have 2 wires attached. They will be just outside where the burners are.

Expert:  Rick replied 1 year ago.

If you still can't find them then post a pic here of the burner area and I'll point them out to you

Customer: replied 1 year ago.
Is this it?
Expert:  Rick replied 1 year ago.

Yes, if it doesn't click when you push the small tan button between the wires then follow both of those yellow wires to see if there are more than 1.

Customer: replied 1 year ago.
The tan button will push down but won't stay down
Expert:  Rick replied 1 year ago.

Then try this, turn the power off and connect the 2 wires attached to the switch together then turn the power back on. If the unit fires up then replace that rollout switch. Do not operate the furnace with the switch bypassed this is for testing purposes only

Customer: replied 1 year ago.
How would I go about connecting the 2 wires together without stripping the sheath off
Expert:  Rick replied 1 year ago.

You can usually insert a small piece of wire into the spade connector once you pull it off the switch. A paperclip can also work. Don't cut the connectors off unless you have more and a crimping tool to replace them. Don't let the paperclip or other bare wire you use to connect touch anything.

Customer: replied 1 year ago.
Like this power is off and I have inserted a paper clip into the 2 wires
Customer: replied 1 year ago.
Now what? Should I turn the power on above and see what happens
Expert:  Rick replied 1 year ago.

Yes if that white wire has bare copper ends and fits tight into the connectors. If so then turn the power on and see if the error goes away and does the burner fire up? If that's a paper clip it won't work with a painted clip. It has to be a bare metal clip.

Customer: replied 1 year ago.
I have tried the wire and the code is not going away. The board will start off with rapid flash and then u hear a click and it goes back to 4 blinks right away
Expert:  Rick replied 1 year ago.

Ok, if you have good contact in the connectors (bare wire tight fit) then the next step is to check for continuity along the yellow wire circuit. You'll need a multi-meter to do this. You can also check all the connection along that yellow wire from end to end (where it connects to the control board).

Customer: replied 1 year ago.
Should I turn the power off again to trace continuity or leave the power on
Expert:  Rick replied 1 year ago.

You should do this with the power off. If you do have a meter then check continuity where both ends of that (yellow wire) circuit connect to the control board. If you have continuity then the board is suspect. If you don't then you have to trace along that yellow wire and test every device you find for continuity and a good connection.

Customer: replied 1 year ago.
What will the readings look like on the multi if there is or is not like 0 or some other number if nothing or if I get a number reading then there is a fault with the board?
Expert:  Rick replied 1 year ago.

You need to set the meter to OHMS. If you have continuity then the meter will read a very low (probably single digit) number. If there is a break in the circuit due to a bad connection or a bad device then it will read infinity or OPEN CIRCUIT. If you read a low number then the board is suspect.

Customer: replied 1 year ago.
What should I set the meter to
Expert:  Rick replied 1 year ago.

Just answered that. Be sure the power is off to the furnace.

Customer: replied 1 year ago.
There is a series of numbers ranging from 2000k to 20k then 2000 and 200 with no k then a sign with an arrow pointing toward a + and a sign that looks like a snake slithering at right angles. Which do I use
Expert:  Rick replied 1 year ago.

Doesn't matter but but the lowest setting is probably best. I guess that snake is the omega symbol which is the symbol for ohms.

Expert:  Rick replied 1 year ago.

Once you set it touch the probes together. You should get a 0 or close to it reading. The reading with the probes apart is open circuit or infinity.

Customer: replied 1 year ago.
I have touched the yellow wires with the probes and I don't get any readings should I touch opposite ends of the same wire with the probes or should I touch the point where they are hooked up to the furnace
Expert:  Rick replied 1 year ago.

you need to probe where they connect to the control board.

Customer: replied 1 year ago.
The board that I replaced this am or to the main board
Expert:  Rick replied 1 year ago.

The main control board where you're seeing the blinking LED

Customer: replied 1 year ago.
none of the tracing I did yielded any discontinuity results. In the end I called an HVAC tech to come look at it and he had it up and running in 5 minutes
Expert:  Rick replied 1 year ago.

Do you know what he did to get it running?

Customer: replied 1 year ago.
There was a loose fuse on the board that he resettled.
Expert:  Rick replied 1 year ago.

That doesn't sync with what you were telling me. A loose fuse means no 24 volt power so no LED flashes and no furnace start up. What ever the actual culprit I'm glad you have it running now.