Carrier 9200 Pressure Switch Problem

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Old 01-02-16, 03:15 PM
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Carrier 9200 Pressure Switch Problem

I have a Carrier 9200 model 58MXA08-12 and I am experiencing a problem with the pressure switch. I had a large wasp nest in the intake pipe which got sucked in to the screen at the top of the combustion chamber. I cleaned this out but still cannot make the pressure switch. I pulled the draft inducer blower and it looked fine. I checked all of the drain hoses and the vacuum lines. Everything is clear. I also blew compressed air through the hoses and fittings.
1. on the small hose from the burner enclosure to the top of the pressure switch, should I be able to feel a vacuum or should it be blowing out?
2. on the hose from the secondary heat exchanger to the bottom of the pressure switch should I have vacuum?
I can attach a hose to the bottom of the pressure switch and if I plug the top hose, I can create a vacuum and the switch will close but only with the top hose plugged. Any suggestions would be helpful. Thanks.
 
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Old 01-02-16, 09:48 PM
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Welcome to the forums.

Typically the small lines to the pressure switch are under a minor vacuum. We use a manometer to actually monitor the vacuum level during servicing.

These condensing furnaces have a lot of drain lines that can cause issues. They can be pretty hard to diagnose online. This furnace is not one of my specialties.

I'm going to leave a link for the startup manual. It describes setup based on orientation. Maybe between that and your questions we can get you running again.

hvac partners/docs/1009/Public/09/58MXA-10SI.pdf


 
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Old 01-03-16, 01:48 PM
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Thanks for the reply. I actually work on large ladle and tundish preheaters in a steel mill (millions of btu's and capable of 3000 degrees). I will bring a digital manometer home from work tomorrow. This furnace is in a machinery repair building on our farm and is not critical but it is suppose to be single digits the next couple of nights here and I would like to get it running. I normally keep it set at 50 degrees and might turn it up a little if I'm going to wash something off.
1.) If I temporarily plugged all the drain lines, would this increase vacuum to the pressure switch just to see if I can get the switch to make?
When I first started working on this, I did find a crack in the drain line that is to be plugged for an uplow installation. I repaired this. There was also a small crack in the small line that connects to the condensate pump. I also repaired this. Then I found the wasp nest. I thought this was the problem for sure since it blocked 90% of the inlet pipe. Reassembled everything and still no luck of the pressure switch making. The draft inducer is running full speed and the inlet pipe has very good draw on it. I'll keep searching.
 
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Old 01-03-16, 03:00 PM
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The specs for the pressure switch should be printed on it.
 
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Old 01-04-16, 01:43 PM
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Ummm....


In my experience, manufacturer's usually don't include the pressure at which pressure switches should close. That's usually true for Carrier furnaces.

But perhaps yours will have that information on it.

As a general rule, I find that a furnace in good operating condition will have a pressure of about -.5 inches WC being applied to the pressure switch, which will keep the switch closed reliably if it's operating properly.

If the pressure increases to -.1 inches WC, the pressure switch will usually stay open, indicating a problem that needs to be diagnosed.

You've identified several possible problems which could cause the pressure switch to stay open. If you connect up the manometer to the furnace properly, you can measure the pressure being applied to the pressure switch.

Of course, without definitively knowing thwe pressure that ought to be applied, knowing the pressure might not be enough to diagnose the problem.

I've always thought that information of the recommended pressure ought to be on the furnace rating plate.

Anyway, good luck. Let us know what you find.
 
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Old 01-04-16, 02:51 PM
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Ok I hooked the digital manometer to the hose that runs from the collection box to the bottom of the pressure switch and started the draft inducer. I had -3.3 in/h20. I then disconnected the tube from the burner enclosure that goes to the top of the pressure switch and read -0.6 in/h2o. I then disconnected the the other hose from the opposite corner of the collection box that runs to the condensate pump. This also read -3.3 in/h2o.

The pressure switch doesn't have any markings which indicate how much vacuum it takes to operate it. Next step was to connect a hand pump vacuum used for brake bleeding to the bottom of the pressure switch. I hooked a multimeter to the actual switch. The switch would flutter at -5 in/h2o but I couldn't pump fast enough to keep the switch made. I removed the top hose from the pressure switch and plugged the hole. Now the pressure switch makes at -5 in/h2o and holds shut. As soon as I unplug the top port, the switch instantly opens up.

I have been starting the furnace by jumpering the pressure switch when the draft inducer turns on just to heat the building up and then shutting everything off when I get it back up to 50 degrees or so. The furnace seems to heat fine. I plugged a carbon monoxide detector in by the furnace and it is not reading anything so I'm not putting CO into the building.

Thanks for the replies!
 
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Old 01-04-16, 03:10 PM
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It looks like HK06NB124 is the part for the pressure switch.
It also looks like it's rated at 1.81 In.WC

High fire make 1.81"WC..... break 1.51"WC.
 
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Old 01-04-16, 04:55 PM
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Thanks, I'll start looking for a pressure switch.
 
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Old 01-08-16, 07:33 PM
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New pressure switch arrived today. Five minutes to install it and I'm back in business. Thanks for you help.
 
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Old 01-11-16, 11:42 AM
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<<he pressure switch doesn't have any markings which indicate how much vacuum it takes to operate it. Next step was to connect a hand pump vacuum used for brake bleeding to the bottom of the pressure switch. I hooked a multimeter to the actual switch.>>



That's very creative!
 
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