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Old 03-04-2011, 06:31 PM   #1
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lennox xp15 high pressure fault code


UPDATE: The problem was a failed thermistor in the garage furnace. It had nothing to do with the heat pump.


Hello, I have a 1-1/2 year old lennox xp15 heat pump.

This morning at 33 degrees outside temperature, the HP turned on by itself, as thermostat was setback to 64 degrees. We noticed the HP sounded especially loud. The HP turned off after 5-7 minutes, then turned on again normally, at which time I woke up and turned up the thermostat to 70 degrees. When I left to go to work 9am, the house temperature was as 67 degrees and seemingly running normally. .

My son was home from school today and at 2pm, the house was up to 70 degrees and my son noticed a smell, but he can't describe it for me.

I returned home at 3pm and noticed the thermostat said "heat on" but I didn't hear the HP noise. I lowered the thermostat and the "heat on" turned off. I waited, then turned it up to 72 degrees, and the "wait" came on, the "heat on", but I never felt warm air come out. Current outside temperature is 45 degrees.

The breakers were okay. I turned the HP and furnace breakers off, cleaned the air filter, turned it back on. Waited, "heat on" but nothing. I turned the temperature to 67 degrees and it turned off.

I went outside and opened up the HP, both green/red simultaneous slow flash"-normal operation, but the HP was off.

So I went inside and turned it back up to 72 degrees and went outside and noticed the HP was making noise, then it shut off and I got the fault code of "green slow flash and red off"--High pressure fault.

1. restricted airflow over indoor or outdoor coil
2. improper refrigerant charge in system
3. improper metering device installed or incorrect operation of metering device
4. incorrect or improper sensor location or connection to system.

I called the furnace installing company and have an appointment for them to come out Monday afternoon. I have to pay for the service charge and labor, but the parts would be under warranty.

The coils (#1) should be fine, area is completely clear and not much pollen, leaves, debris around here.

Is there any other simple stuff I can do to trouble shoot/fix the problem, hopefully to avoid the service call?

Thank you in advance


Last edited by GEAF; 03-11-2011 at 08:45 PM.
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Old 03-04-2011, 06:49 PM   #2
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lennox xp15 high pressure fault code


"Cleaned the air filter". Is that one of the washable foam filters or an EAC? If it's a washable 1" filter try replacing it with a cheap disposable one. Turn the power off at the furnace and then back on, that will reset the pressure switch lock out on the heat pump.

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Old 03-04-2011, 07:24 PM   #3
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lennox xp15 high pressure fault code


sounds like a possible bad indoor blower motor.... bad smell inside and high pressure tripped outside in heating mode.......... Most likely a blower issue.
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Old 03-04-2011, 07:33 PM   #4
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Thanks Marty S, yes it is a 1" washable filter and I've been thinking to switch back to a basic disposable filter. I do vaccuum/wash the washable filter monthly.

HVACTech, I think though you may be right. So, we decided to give up on the HP and turned on the emergency propane gas heat. After 15 minutes, notice no heat and no fan, even though the thermostat said "aux heat on"

So we checked our furnace in the garage and just got the fault error code 44-blower calibration fault on our Carrier 58mvp furnace, going on 11 years of age.

So I'll have to search prior threads, but basically do we need to replace the blower motor? Is it a very handy DIY type job?

Also just got the fault code 41.

So does this mean my Lennox HP is okay, just reacting to my blower problem in the Carrier furnace?

Last edited by GEAF; 03-04-2011 at 07:50 PM. Reason: add question
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Old 03-04-2011, 08:09 PM   #5
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lennox xp15 high pressure fault code


correct, most likely HP ok and just blower issue. Prob not a DIY job, hard to get parts for VS motors if not a PRO.
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Old 03-04-2011, 08:13 PM   #6
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Yep that means the heat pump was just protecting itself from the blower problem. I'm not positive but believe that motor is ECM. If so and it's 11 years old(out of warranty) your going to cry like a little girl when you see the price.
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Old 03-04-2011, 08:20 PM   #7
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Thanks again. In researching, found this thread and will try to open up the blower tomorrow to see if it could be the $5.00 thermistor. Looks like I'm lucky to get 11 years out of the blower regardless. Also any estimate on costs to replace the blower + labor.

Carrier 58MVP Blower Problem

These high efficiency variable speed blower motors are maufactured by GE. They are used in many brands including Lennox, Carrier, Bryant, Payne, York and Trane.

There are two parts to the blower motor.

The two parts are the motor itself and the ECM module that is attached to the blower motor. The ECM looks like a black hubcab and it is attached, to the motor, with two long bolts.

You can remove the ECM module by simply unscrewing the two long bolts. You do not have to remove the blower motor from the mounting.

The motors in different series and brands are often the same. The difference is the ECM module. The ECM module must be matched up exactly or it will not work.

What usually fails on these high efficiency units is the ECM module. A service [COLOR=blue ! important][COLOR=blue ! important]truck[/COLOR][/COLOR] can not possibly carry all of the hundreds of ECM modules that are used in the various brands and series of brands.

However, the part that often fails in the ECM unit is part number SG379 which is a black disc about the size of a quarter in the center of the ECM.

You can look at the SG379 disk and often tell it has failed without any further checking. The disk will often be broken, brittle or disconnected from the circuit board, and there will be an obvious spot on the circuit board that has received a lot of heat. As long as the board is not broken, or deformed and the traces are in place, then this componet can be replaced. This component is designed to take a lot of heat and the circuit board will be discolored from the heat. This is normal and this is common.

This propierity part is a thermistor and it is used for surge protection as well as regulating the current to the motor.

SG379 has a finite life and like a light bulb it gets weaker and weaker until it finally just fails.

Although not available from GE or any or the HVAC companies, a SG379 part substitute, manufactured to OEM standards, is available from amazingkeys.com and can be soldered into the ECM circuit board in about 5 minutes.

If you are a serviceman, you can keep a few of these parts on your service truck and have the unit up and running in one service call and not have to replace the motor or the ECM. This also saves the customer a $1500 blower motor replacement or an ECM replacement.
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Old 03-05-2011, 02:08 PM   #8
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lennox xp15 high pressure fault code


Update: Found the thermistor in my carrier 58mvp has clearly failed. part Number sg379 written on the part.

I can get the exact part at amazingkey.com for $19.99
Appears other vendors have it for cheaper, but they are different part numbers/brand
I believe the specs are 1ohm, 20amperes and are equivalent at all vendors

mouser electronics
digikey
newark

I certainly don't mind spending $20 for a repair and exact part replacement, but any thoughts on non-oem replacements raging from $1.50-$10.50ish?
I'm going to a local furnace supply shop first thing Monday morning to see what they may have in stock, but otherwise will place an online order Monday morning.
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Old 03-05-2011, 02:24 PM   #9
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Call and cancel that service call now,, so they don't knock on your door Monday and bill you a trip charge.
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Old 03-05-2011, 02:42 PM   #10
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lennox xp15 high pressure fault code


Thanks beenthere, MartyS and hvactech. I appreciate all of your help. I will update this on Monday or whenever I get the part, hopefully with a happy ending success story.

Now time to go stack some more wood for the next few days. Also going to shopvac and use the air compressor to really clean the furnace out.
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Old 03-11-2011, 08:44 PM   #11
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lennox xp15 high pressure fault code


Success! Replaced the thermistor in my furnace today that was ordered from newark.com and the furnace blower started right up. It ended up being the 1ohm, 30amperes and the size was equivalent to the OEM sg379. Thanks everyone for your help!

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