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Brian HVAC Guy
Brian HVAC Guy, HVAC Technician
Category: HVAC
Satisfied Customers: 770
Experience:  I have been an HVAC/R mechanic/technician for 30+ years.
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I have a GMH950703BXAF Goodman

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 I have a GMH950703BXAF Goodman I bought a Honeywell RTH8500WF Thermostat installed and someone messed up namely (ME)one of the wires. thought they would just take apart with no reference.

The fuse on the main board was BLOW. replace that and have a heartbeat! But I have the red 3 code flashing.. lights Pressure switch stuck closed.
it turns it on all you hear is the blower is just spinning. no control at t-stat.
is there a manual reset for the presser switch?

Need help with wiring??

I have 2 little wires that go the the ac unit outside.
I think they connect to Y and C on the main board?


click to see pic

Ac Out side unit

to the main board inside wiring

and here is the thermostat wiring

You can see there us a 3wire red green white
(green) G
(white) W
and 2 wires
(Red) R
(White) C

Now there is a pump on the side of the unit

A pump of water needs 24 volts looks like it turns on when water needs to be pumped?

out side ac wires


inside ?? y & C


pump on side of unit


Main board wiring


t-stat wiring

Brian HVAC Guy :

Hi, I'm Brian and my goal is to diligently answer your HVAC/R questions to your complete satisfaction! It sounds like you could use a helping hand. I'm here to help and hopefully we can figure your issue out together!

Brian HVAC Guy :

I see you are standing by, are you receiving my chat messages?

Brian HVAC Guy :

I am going to switch to the question/answer format instead of the chat format in case you are not receiving my chats.

First I want to thank you for the model numbers and the pictures. It really helps us when troubleshooting problems. Ok let's get to it. First let's tackle the wiring:

The two wire cables from the thermostat and condensate pump:
R/RC (red wire) on stat to red wire on condensate pump cable (use a small wire nut)
White wire on condensate pump cable to R on ahu control
C (white wire) on stat to C on ahu control

The Three wire cable from the thermostat:
W (white wire) on stat to W on ahu control
Y (red wire) on stat to Y on ahu control
G (green wire) on stat to G on ahu control

The two wire cables going to the condenser (outside unit)
White wire from condenser to C on ahu control
Red wire from condenser to Y on ahu control

That will complete the thermostat wiring. The wire going to the condensate pump is a safety cut-off so if the condensate pump stops pumping water out it will stop the system and the unit won't produce anymore condensate so you won't have water everywhere.

Now for the 3 flash code. You are correct that it relates to an inducer draft blower pressure switch issue but it is not stuck closed, it is indicating that the inducer blower is running but the pressure switch is not closing it's contacts to tell the system that it is ok to fire up the burner. There are quite a few things that could cause this. If the inducer is operating correctly and is supplying the burner with air properly then the problem lies with the pressure switch. The first thing I would do is (with the power off) disconnect the tubing and with a can of compressed air blow the tubing and fittings clear as sometimes they can get clogged. Reattach them and see if that worked. If that doesn't work make sure the flue or inducer air pipes are not clogged anywhere especially at the ends. Make sure the flue isn't filled with condensate from the furnace. Make sure the inducer blower wheel is attached securely to the inducer motor shaft and the blower wheel is clean. Those are the main things to check with an inducer airflow switch issue. If you still can't get the unit to work properly, please message back and I will troubleshoot the system further with you.

Thanks for using Just Answer and good luck!

Customer: replied 3 years ago.

OK wiring Done.. thanks I remember you are correct with the wire nut..


the system is only a year old and work perfectly before I messed with it..


don't see any clogged tubes/ lines there is pvc piping running from the furnace to the out side as a vent


here a pic of the upper unit with the cover off



3 code


can you point out in picture






There is no manual reset for the inducer draft pressure switch(s) and they are not adjustable. The link below is to your furnace installation and operation manual. It outlines the location of all components. From your picture it appears everything is installed properly. It seems a bit odd that a pressure switch would fail just because you had some wiring issues replacing a thermostat but stranger things have happened. The pressure switches are the round black devices with the flexible black tubing attached to them. These are the devices that the code 3 is referring to. It appears there is an issue with one of them. Double check that the wires are firmly connected to the pressure switches, it looks like there may be an issue with the wire connections on the pressure switch on the left. If you have access to a multimeter I can guide you through a basic check of the pressure switches. If this doesn't solve your issue it may be time to call in a tech to get to the root of the pressure switch issue. Please message back if you have any further questions.

IO-299P 10-2012.pdf
Brian HVAC Guy, HVAC Technician
Category: HVAC
Satisfied Customers: 770
Experience: I have been an HVAC/R mechanic/technician for 30+ years.
Brian HVAC Guy and other HVAC Specialists are ready to help you
Customer: replied 3 years ago.

Well problem solved


Watch a u tube video on how a presser switch works in the a furnace . I am a automatic by trade, so i know how to test vacuum and operated switch.

Look like this system is in place so houses don't burn down!! You HVAC guy got us covered thanks.


Well problem solved right side presser switch stuck.. open


With vacuum left side OK right no continuity . With a little Blow and suck LOL it started I got continuity from the right side. System is up and running I think I should order a presser switch it may get stuck again..








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