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Category: HVAC
Satisfied Customers: 14389
Experience:  15yrs in the HVAC industry with certificates and degrees.
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Havoc low voltage issue, 3 days, yes, calling for cool blows

Customer Question

havoc low voltage issue
JA: I'll do all I can to help. How long have you been dealing with this?
Customer: 3 days
JA: Do you plan on doing the work yourself?
Customer: yes
JA: Anything else we should know to help you best?
Customer: calling for cool blows the panel fuse
Submitted: 6 months ago.
Category: HVAC
Expert:  HVAC Guru replied 6 months ago.

Hello, one minute while I get some information together.

Customer: replied 6 months ago.
OK it is a lennox c33-30b-2f-3
Expert:  HVAC Guru replied 6 months ago.

Hello and thanks for using this service! If you are a JA Member I would like to personally thank you and welcome you back! I am HVAC Guru an extremely experienced tech on the site and I try to get to as many customers as I can. NOTE it takes time for me to type research and add links so please wait for me to respond back I can only do this so fast. Secondly, I do not know your skill level so please try and let me know if I am going beyond your knowledge or comfort zone thanks! I strive for a 5 star rating from everyone especially our JA members.


You need to remove 1 thermostat wire at a time from the board starting with the Yellow wire then try it to narrow down which one is causing it to blow. The you will have to trace the wires to see if one is rubbed through or there is a bad connection on the wire. One of the thermostat wires is typically causing this issue.

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Customer: replied 6 months ago.
The panel fuse blows when calling for cool. It works with heat.I have disconnected all LV wires to the ACThe fuse doesn't blow As soon as I connect them at the board the fuse blows immediately on start up
Expert:  HVAC Guru replied 6 months ago.

Yes then you need to put one wire on at a time to see which one is causing it or run a new thermostat cable.

Customer: replied 6 months ago.
I have ohm d the wires i get 1.6 ohms between them. I even connect an unused green wire and same thing happened . This is with them DC at AC
Customer: replied 6 months ago.
Ok I have two fues left I will try one at a time now
Customer: replied 6 months ago.
I'm out of fuses. Both white and red wires blew the fuse when the were individually connected to the Y terminal.They are disconnected outside
Customer: replied 6 months ago.
Just one wire at a time
Customer: replied 6 months ago.
Posted by JustAnswer at customer's request) Hello. I would like to request the following Expert Service(s) from you: Live Phone Call. Let me know if you need more information, or send me the service offer(s) so we can proceed.
Customer: replied 6 months ago.
I don't want to pay any extra charges just advise me what I should do now I did one wire at a time at the Y terminal and continue to blow the fuse is
Expert:  HVAC Guru replied 6 months ago.

OK then remove the G wire

Customer: replied 6 months ago.
I replaced the whole wire to the ac. The fuse no longer blows. But now the unit won't start in either heat or coolTwo slow flashing lights. I have it on heat now with the ac low voltage wire DC. Nothing but blinking lights.
Expert:  HVAC Guru replied 6 months ago.

Read the error code on the back of the panel for the two slow flashing lights...I think that is in standby waiting for a signal from the thermostat.

Customer: replied 6 months ago.
Two slow flashing is normal operation. I have three t stats here and have tried them all.
Customer: replied 6 months ago.
The transformer secondary is 28vac
Expert:  HVAC Guru replied 6 months ago.

Jumper R to W at the board and see if the heat comes on if it does something is wrong with the thermostat wiring or thermostat...also make sure you have the switched depressed on the panel on the furnace or it will not work.

Customer: replied 6 months ago.
I did that and heat cane on. Switched that's and heat comes on. Cool comes on now at the handler but nothing outside.Getting voltage on c and y so the switch on the compressor?