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Billy
Billy, HVAC Technician
Category: HVAC
Satisfied Customers: 19723
Experience:  Endorsed for unlimited heating, cooling, oil burners, boilers, refrigeration, hydronics
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I have situation on our Carrier furnace. The diagnostic light

Resolved Question:

I have situation on our Carrier furnace. The diagnostic light is blinking 4 times and repeating. I already removed the furnace filter (very dirty) and powered off for 5 minutes ... then powered on again. That diagnostic light is still blinking 4 times. Can you help me?
Submitted: 4 years ago.
Category: HVAC
Expert:  Billy replied 4 years ago.
Chat Conversation Started
Billy :

The Carrier usually is a 2 digit code. example: short blink, short blink, short blink,...long blink = 31. Are you positive it is 4?

Customer:

Yes ... There is a pause after each 4 flashes ... then it repeats

Customer:

If you want me to locate the model of the Carrier furnace - I can do that

Customer:

I can't tell if you are thinking or you left me .. Can you ping me back to let me know that I'm still a customer?

Billy :

The unit is variable speed motor?

Customer:

I don't belive that is true ... it is 16 years old and there are no noticable variations in speed at all

Billy :

The code is for a blower lockout which is associated with variable speeds units like MPV. Can you pleas get model number

Customer:

sure .. where will I find that model number - on a plate or inside the control area?

Billy :

Inside upper compartment

Customer:

I apologize .. I relly messed you up ... The unit above says Carrier ... The lower fubnrace unit says YORK ... Inside the unit the model is P2MPD08W04801B

Billy :

Ok this makes more sense...code 4 on York P2 unit is open limit. On the front wall of the furnace, do you see a 2"x3" rectangle flat plate with 2 wires attached?

Customer:

I should have taken my laptop down stair with me ... I will be right back while I run down and check

Customer:

Yes I saw it ... two large guage wires - one red and one white

Billy :

Tap that switch and see if codes ceases. If not remove and tap bulb end and reinstall. Try and let me know

Customer:

will do

Customer:

are you instructing me to do this with the powere on?

Billy :

off...and then back on

Customer:

ok

Customer:

ok .. I tapped both the limit switch and lamp ... no change, so ... I removed the switch form the wall and cleaned it off (tiny bit of dust) ... tapped it and checked all the connectors - everything seemed in order ... Power it back on and no change - I still have the 4 blinks from the diagnostic bulb

Billy :

Now remove the two wires and touch directly together thus bypasing switch. Make metal ends touch of wires...if plastic coated use a paper clip to insert into each and loosely tape so meatal does not touch cabinet

Customer:

Sorry ... There were storms in our area last night and I lost power for 2 seconds ... just rebooted and back now ...

Customer:

I see what you want me to do ... I will connect those two wires together and bypass the wsitch ... heading downstairs now

Billy :

There is also a roll out switch may be included in that code sequence...but we will eliminate the main limit first

Customer:

You are a genious sir ... That bypass did the trick ... I had to resort to a paperclip, but I bypassed the switch and powered on ... The diagnostic lamp remained dark ... and the glow from the igniter turned on ... I turned off the power at that point since I saw that you figured out the problem - bad limiter switch.

Customer:

Does that make sense to you that I need to replace the limiter switch?

Billy :

You are correct. Apparently either due to plugged filter..OR...loss of power durning heat cycle made the switch trip and it did not reset. One last test you can try is to remove switch....hold sense in air stream of hair dryer...get it warmed good and then put in freezer...quite often the extreme will reset the switch. I still recommend replace though eventually

Customer:

I think I'll take your advice and replace it now ... How would I find the part number?

Customer:

Wow .. $81 ... the last one you showed me was $56 ... Do these prices vary that much? I need the heat today, so I was going to find a local place. Are there variations in the switched that are of low quality and I should make sure I get that exact part number?

Billy :

All you need to do is get the same temp range...any limit switch will do the same thing. Every store has different mark up...see this one - http://www.gsistore.com/yo02170op140.html I would take off and take it to a heating repair shop and just get a replacement.....yours opens at 170f and is supposed to close at 140f

Billy :

as long as you get a lmit with a open value of 170f you are ok

Customer:

That's great ... I think your service is excellent ... You were patient and right on the mark each step of the way ... God Bless you for your excellent help ... thanks you.

Billy :

You are very welcome and I wish you luck!

Billy, HVAC Technician
Category: HVAC
Satisfied Customers: 19723
Experience: Endorsed for unlimited heating, cooling, oil burners, boilers, refrigeration, hydronics
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