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Hi - I have two Goodman furnaces, but Im having a problem

Hi - I have two Goodman...
Hi -

I have two Goodman furnaces, but I'm having a problem with one. I keep getting a pressure switch stuck open/closed error. We switched the control boards between the units (it was the same board) and I still get the same error. Do you have any other ideas as to why the pressure switch error keeps happening?

Thanks.
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Answered in 1 minute by:
11/18/2013
Rick
Rick, HVAC Supervisor
Category: HVAC
Satisfied Customers: 23,075
Experience: 40+ yrs. experience as a licensed oil & gas technician.
Verified

Rick :

Welcome, my name is XXXXX XXXXX I will do my best to help you with your issue.

Rick :

You could have a bad pressure switch or there could be a blockage in the exhaust vent

Customer:

HI

Rick :

Or your draft inducing fan could be weak and not provinding adequate draft

Customer:

when the unit comes on we hear the click in the switch

Customer:

doesn't that mean it's working?

Rick :

I don't think your hearing the pressure switch click

Rick :

You might be able to hear it if the fan wasn't running

Rick :

but the fan makes too much noise for you to hear the switch

Customer:

yes...we do hear a click when the service panel is open and you put your ear next to the switch

Customer:

yes the fan does make some noise, but if you listen carefully i hear a small click

Customer:

is there a way to test the pressure switch?

Customer:

or to test the draft inducing fan?

Rick :

You can check for continuity through the switch with an ohm meter. You need a manometer to check the draft

Customer:

this is a Goodman high efficiency furnace

Rick :

Same procedure no matter what furnace you have

Customer:

the unit works if we replace the switches with ones that have lower gauges

Rick :

"lower gauges"?

Customer:

lower sensitivities

Customer:

there is a number on the switches

Rick :

Then that could be an indication of a draft problem

Customer:

ok...what types of draft problems should I check for?

Customer:

the exhaust vent is clear

Rick :

How do you know that? It could be a blocked vent (including any sags in horizontal vent piping runs) or could be a weak fan (only a manometer test will confirm this)

Customer:

the vent is made of 3 inch pvc piping

Rick :

sags can fill with water (condensate) restricting the air flow

Customer:

the piping is rigid so any condensation should drain

Rick :

BotXXXXX XXXXXne is you need a manometer to be sure. The fact that the unit runs with a switch that has a lower pressure rating indicates a draft issue. If you are sure there are no vent obstructions then the fan is the most likely culprit or possibly too long a vent run. A too long vent run doesn't always cause a problem at first but it can show up as the fan output weakens a bit over time

Rick :

One other possibility and it might not apply to your unit

Rick :

Some unit have a condensate drain at the beginning of the run. If the drain is (partially?) plugged this too can affect the draft. The only other possibility could be a (partial) blockage where the vac tubes connect to the furnace (not the switch)

Rick :

You can try poking a straightened paper clip into the hose port on the furnace (not the switch)

Customer:

there are two tubes...on going into the furnace and the other into the fan?

Customer:

what can clog the tubes? water?

Rick :

Water can clog the tubes but it usually shows in the tubes and you said you cleaned them. Blocked ports are rare but they do happen. They can get blocked by debris as well

Customer:

ok...I'll try cleaning the ports...if the manometer shows the fan is too weak...how much of a stronger fan would I need?

Rick :

You should replace it with the OEM (original equipment) fan. The only reason the orignal fan wouldn't do the job is because the run is too long

Customer:

if the run is too long what would be the corrective action? moving the furnace?

Customer:

the holes in the unit are for two inch pipes and we put three inch

Rick :

Take a different shorter route with the vent.

Customer:

so i though the three inch pipe would compensate for the longer run

Rick :

The size of the vent piping is determined by the furnace btu input and the length of the run. I only mentioned the length of the run as a possibility. I wasn't saying it was likely

Rick :

The vent length limits are listed in the installation manual

Customer:

ok...i'll double check the limits for the length of the run...so to recap it good be clogged ports, a weak fan or the run might be too long...any other possibilities?

Rick :

Check the vent condensate drain (if you have one) for blockages. It could also be the original switch too is faulty. Even though you hear it click doesn't mean it's making good contact. You need to check for continuity through the switch while the fan is running or check for 24 volts (to common) in and out of the switch while the fan is running.

Customer:

the unit is only two years old...do the switches go bad that often?

Rick :

These switches work on extremely low pressure so they are very sensitive. Consequently they can fail at any time. It's not common for a switch to fail in 2 years but it does happen

Customer:

if it's a switch issue, should I replace both at the same time?

Rick :

It's best to determine which one is the culprit in this case. If your unit was 20 years old I'd say replace them both.

Customer:

so since the unit works with switches with lower pressure ratings then would the more probable cause be the switch instead of the fan?

Rick :

No way to know from that alone. Could be either one

Rick :

are you still there?

Customer:

yes

Customer:

ok...the problem is recurring as well

Customer:

we were able to get the unit to work by resetting the control board, the unit works for sometime and then the problem happens again

Customer:

does this indicate anything?

Rick :

Could point to a balky pressure switch. Sometimes it works sometimes it doesn

Customer:

what do you mean by balky?

Rick :

sometimes it works sometimes it doesn't

Customer:

i see...ok...thanks for your help

Rick :

You're welcome!

Rick
Rick, HVAC Supervisor
Category: HVAC
Satisfied Customers: 23,075
Experience: 40+ yrs. experience as a licensed oil & gas technician.
Verified
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Satisfied Customers: 23,075
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