York Diamond 80 Bad Pressure Switch?


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Old 12-10-14, 07:37 PM
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York Diamond 80 Bad Pressure Switch?

I came home to no heat from my York Diamond 80 (P4HUC20N09201A - upflow/horizontal) furnace. The diagnostics control was flashing 2 red lights which the manual indicates is an issue with the pressure switch: "This indicates that the normally open pressure switch contact are stuck in the closed position. The control confirms these contacts are open at the beginning of heat cycle. This would indicate a faulty pressure switch or mis-wiring." I found the following thread (http://www.doityourself.com/forum/ga...ot-coming.html) and tapped/smacked the pressure switch a few times and the furnace fired up and it is working fine. I read several threads on various forums that indicate the pressure switch is rarely bad. Should I replace the switch or wait for it to happen again (e.g. assume anomaly?) If so, where do I get the part number from? The previous owners documentation is from Source1 HVAC Service Parts but it is of the P4DN series (not sure why they have that if the furnace is P4HU...).

Thanks for help in advance.
 
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Old 12-10-14, 09:02 PM
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Here is a link to the parts manual for your furnace:

http://www.master.ca/documents/Repair_P4HUA_B_404.pdf

As shown on page 5 the pressure switch (switch, air pressure) part number appears to be 024-27630-001.

You are correct that the pressure switch rarely goes bad. It is usually doing it's job and indicating there is another issue that needs to be corrected. Sometimes the contacts inside the pressure switch go bad and cause issues. Many times it is the port where the pressure switch hose connects to the inducer motor (collector box for some models) that causes the issue. The small hole in that port gets clogged up with crud such as rust and needs to be reamed out with an opened paper clip making sure it is clear all the way through. Here is a link to a thread posted earlier today where that simple procedure cleared up his issue:

http://www.doityourself.com/forum/ga...rol-board.html
 
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Old 12-11-14, 07:11 AM
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Thanks for the reply. I'll check the incoming house to see if there is any blockage or at the nipple area. If none, should I still replace the sensor? I have no issues right now but I am not a big believer of "it just happened once".
 
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Old 12-11-14, 07:50 AM
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I wouldn't replace the pressure switch yet. Have you checked the pressure switch for continuity to see if the switch contacts are actually stuck closed. To do so, remove the wires from both terminals of the switch. Place voltmeter on ohms setting and place a probe on each terminal. You should get a reading of 0 or very close to 0 ohms if the contacts are closed. Have you checked the condensate drain system to ensure it is not clogged/restricted, checked the vent pipe to ensure there is nothing restricting it such as leaves, bird's nest, bee hive, dead bird and etc. It could be a problem with the inducer draft motor. The best method to check the pressure switch is to use a manometer to see if the inducer is producing enough air flow to close the pressure switch. If it is then that would point to a bad pressure switch. If it was not producing enough air flow then it would point to a problem with the inducer. But, I would first start by checking to see if the contacts are stuck closed inside the pressure switch and go from there.
 
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Old 12-11-14, 08:08 AM
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I am comfortable checking via volt meter but I am not sure where the condensate drain system is located, vent pipe (actually is that the inlet to the switch?), or the inducer draft motor. I agree. Let's start with the volt meter test. However, I thought there were a couple different terminals on the switch but I could be mistaken.
 
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Old 12-11-14, 09:06 AM
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Yes, there are two terminals on the pressure switch. If memory serves me, the wires are blue and white. Remove those two wires and test for continuity across those terminals. The vent pipe is the exhaust pipe that goes to the outside. In your case, you probably only have a single metal pipe going to the outside.
 
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Old 12-11-14, 10:23 AM
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[SUP]Thanks. I'll check this weekend as everything is still going well. Given this occurred once, do I more than likely have a problem or could this just be a hiccup? Trying to determine priority...[/SUP]
 
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Old 12-11-14, 10:35 AM
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Since tapping the pressure switch allowed it to operate again it may have just been a sticky contact. i suggest you monitor the operation and see if any flash codes are observed.
 
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Old 12-11-14, 10:52 AM
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Thank you sir for all your help.
 
 

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