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Matthew
Matthew, HVAC Technician
Category: HVAC
Satisfied Customers: 1994
Experience:  14 years experience in the HVAC field of service, installation, Manual J & D calculations
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I have a Concord furnace model # CG80TA100D20CL a Honeywell

Resolved Question:

I have a Concord furnace model # XXXXX a Honeywell gas valve SV9520H 8026. The A/C works but on a call for heat, the T-stat send 24 VAC back to the blower control center. The inducer blower does not start. I checked for voltage (is it 24 or 120 VAC)? I saw 2.5 VAC. The valve LED flashes multiple times and then starts a two flash operation showing that the pressure switch is closed although it is open. I pulled the leads and it reads open; especially since the blower is not run. The main circulation fan is running. Is the inducer supposed to be running immediately on a call for heat. The LEDs lights don't match the problem. It appears to be a board problem but I need help to determine if the inducer blower is bad, there is a safety lockout, a bad blower control board, or bad smart valve.
Submitted: 3 years ago.
Category: HVAC
Expert:  Matthew replied 3 years ago.

Matthew :

Hello, My name is XXXXX XXXXX I will do my best to help you today.

Matthew :

Inducer motor comes on immediately it runs off of 120v you should be able to take the two wires hooked to it off and put one test lead on each from your volt meter then push in the door switch and it should have 120v if you have W and R jumped to call for heat. If you are getting the pressure switch is closed error then this would cause the inducer to not come on. If the board is getting the signal that the pressure switch is closed before the inducer is energized it will never energize the inducer it will just go straight to the 2 flash pressure switch stuck closed code.

Matthew :

If you pull one wire off the pressure switch and then start up the furnace again and it still says pressure switch stuck closed then one of two things is going on. A. the two wires going to the pressure switch are bare and touching each other simulating a closed pressure switch or the control board is bad and not reading what is actually happening.

Matthew :

hold on sorry back up

Matthew :

This is a smart valve so the pressure switch wires hook into the valve. These things are terrible when it comes to losing signal through these plugs. Most of the time it's the igniter plug that gives the most troubles not sensing the flame, but the pressure switch and limit circuits are known to give problems too.

Matthew :

try wiggling the plugs and pressing in on them see if you can't get it to bring on the inducer.

Matthew :

I have taken a small zip tie and tightened these plugs down by wrapping the strap around the valve and over the plug, but this has only ever really worked a couple times most often you have to replace the valve. My wholesale house sales rep calls these smart valves "stupid valves"

Customer :

How would it give a pressure switch closed in this instance?

Customer :

This is the funky diagnostic I received.

Matthew :

The plug is shorted where it hooks to the "smart valve" Telling it that the wires have continuity when they shouldn't

Matthew :

These valves do some funky things

Matthew :

If you unhook the plug from the valve then you get the open limit switch code so there is no good way to test it. They are a troubleshooting nightmare.

Customer :

In this case, do I need to replace the entire valve or only the electronics?

Matthew :

There is a special tool honeywell came out with to specifically diagnose a smart valve but it costs over $600.

Matthew :

The whole valve they don't sell the power cell on top seperate

Customer :

How much do you think the valve costs?

Matthew :

That is the cost you would be paying if you get a tech to put it in. Our cost from a wholesale house is around $150

Matthew :

You may could find one online for that $150 cost

Customer :

I will look into replacing the valve. I simply wanted to make sure it was the valve, especially since the inducer did not fire when in heating mode. It does appear to be difficult to troubleshoot these valves. The diagnostic threw me off and I appreciate your help. If you can think of any other checks before I replace the valve, I would appreciate the heads up.

Matthew :

I will bet you money that if you sit there and wiggle the plugs around while the system is starting to fire you will get the inducer to kick in.

Customer :

Could you give me a short heating mode sequence. For example, on call for heat it does step1, step 2. Thanks

Matthew :

inducer fires up

Matthew :

this pulls in the pressure switch

Matthew :

This allows the igniter to energize

Matthew :

Once fully energized the valve opens and gas hits the igniter lighting the burners

Matthew :

The flame sensor senses the burners

Matthew :

Sends signal to control board to bring on the blower.

Customer :

Thank you for your help

Matthew, HVAC Technician
Category: HVAC
Satisfied Customers: 1994
Experience: 14 years experience in the HVAC field of service, installation, Manual J & D calculations
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