COMMUNITY FORUM

mattb8888

01:18PM | 12/15/04
Member Since: 12/14/04
8 lifetime posts
Bvhvac
Had a tech inspect my malfunctioning furnace and he indicated that it was the circuit board. Researched my problem and found that similarly described problems were the result of a defective circuit board. I have a carrier gas furnace and replaced the old board, HK42FZ004, with a brand new circuit board #325878-751. Installed it, found the correct homes for all the wires and am stuck at System Check Out (Component Test). The instructions indicate to shut the thermostat off, turn on the power to the furnace and manually close blower door switch. I do this and the blower goes on. No heat or AC. The LED is continously on (no blinks) at this point. The next step is "...with a short piece of wire, briefly short TEST/TWIN terminal to Com/24v terminal." That's where I am stuck. Does this mean to actually take a wire and touch each terminal with it at the same time with the power on? I think that I am just not understanding this part. I can do it, but want to make sure it is done right. Any suggestions from the brilliant and hardworking members of this messge board would be greatly appreciated.

mattb8888

02:10PM | 12/16/04
Member Since: 12/14/04
8 lifetime posts
Was able to connect the 2 terminals to start the component self test, but nothing happened. As per the instructions, when I Turn the power on to the furnace and manually close the blower door switch, I used a piece of test wire to connect the terminals. As per the instructions, the LED is supposed to flash 4 times then turn on the inducer motor... What happens for me is that the continously on LED will go off then after a few seconds blink rapidly until I remove the connection. The Component test sequence does not start.

Any suggestions?

JGRIZZ

06:41AM | 12/17/04
Member Since: 12/16/04
54 lifetime posts
The fan runs continuously because the 24 volt circuit is broken somewhere, and the relay on the board needs 24 volts to open the fan circuit to the blower to keep the fan off during heating. In cooling the relay is deenergized and the blower operates on high speed. trace the low voltage wiring through all of the limit circuits and see if the 24volt circuit is broken. Also besure to check that the t-stat is in the fan auto position, if this is the case then disconnect the green wire to the furnace circuit, in case there is a short in the fan circuit out side of the furnace, if there is the fan will stop running until called upon by the circuit board. If the 24 volt circuit is broken the fan will continue to operate with the green wire disconnected, that is assuming that the wire going to the g-terminal was actually green, if not the color doesny matter as long as it is the g terminal that gets disconnected. leave this wire off until you iscolate the 24 volt problem.

JGRIZZ

06:43AM | 12/17/04
Member Since: 12/16/04
54 lifetime posts
The main wires the black and the white may be reversed, the polarity may be reversed to the board. Simply switch the wires or reverse the plug.

mattb8888

06:59AM | 12/17/04
Member Since: 12/14/04
8 lifetime posts
Thank you for the infomation. I will examine the wires again. I spent a lot of time making sure I connected them exactly as per the instructions, but I can double check.

After the board was installed and all the wires connected, when I turn the power on and manually close the blower door switch, if everything was done correctly, what is supposed to happen? Nothing until after the test sequence? Is there a way to bypass the testing and just see if the furnace will work regularly?

JGRIZZ

06:48AM | 12/20/04
Member Since: 12/16/04
54 lifetime posts
SImply instll the blower door and turn the unit into a call for heat, set to heat and turn the desired temp up as high as it goes.

The induced draft blower should start, a minute or so later the pressure switch will sense a negative pressure in the combusion chambers or a positve pressure in the vent stack, then the hot surface ignitor will begin to glow then the gas will flow across the ignitor and then you should have combustion, the flame sensor will sense the flame and lock in the gas valve and the board will turn off the ignitor. 90 seconds later the blower will start.

mattb8888

10:37AM | 12/21/04
Member Since: 12/14/04
8 lifetime posts
JGRZZ,

I've been following your advice but I just can't get the darned thing to give me heat. I tried bypassing the testing but the furnace just continued operating as previously described.

In your experience, is it possible that it is just a question of a wire or 2 connected to the wrong terminals. For example, there are 2 Aux furnace wires (black and white)coming from the top and a handful of colorful blower wires (red, blue, black, white...)coming from the bottom. When I disconnected the original circuit board, I carefully labeled each wire and where it went. Since the updated circuit board is a little different, I'm thinking something got lost in the translation. For example, the white furnace wire did not seem to go in the same position (relative to the new board) compared to the old board. In your experience, what would be my first step to backtracking (without having to spend a couple of hundred for a tech to come visit ;). Any further assistance would be greatly appreciated. If you can even point me to more specific reference material than these boards, that would be appreciated also. Thank you again for all your information.

JGRIZZ

05:33PM | 12/21/04
Member Since: 12/16/04
54 lifetime posts
I was just looking at your original post, what exactly was the original reason that you had a service technician outhere anyway?

Was your original problem that the fan ran continuously and you got no heat? If so, what is the model and serial number of your furnace?

my email address is

john_grizzco@wans.net

mattb8888

09:51AM | 12/23/04
Member Since: 12/14/04
8 lifetime posts
JGRIZZ, thanks for all your advice. In the end I had to bite the bullet and call the tech. He looked at it (said the circuit board was installed correctly, yeah for me.) and discovered that the wiring between the thermostat and the furnace weren't matched up correctly. ie:Greeen wasn't going to Green. He fixed that within 30 minutes, I wrote him a check for $80 and turned my heat on.

Thanks for your time and advice. Have a great holiday season.
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