2 McQuay Home Units with blowers shutting off intermittantly


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Old 06-06-10, 06:55 AM
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2 McQuay Home Units with blowers shutting off intermittantly

Hi all, I have 4 McQuay units in my how. These are the WWLL model water source heat pumps that provide both A/C and heat. These are 208 volt units. Needless to say they are very expensive. Let me begin by saying these units are precisely 10 years old. I have 4 of them currently 2 do not work properly. I've spent many years working on cars, pinball machines and home appliances - so I thought this would be something I could tackle.

Both of the units shut down and show a "Hi Pressure fault" reading on the led indicator. After unplugging and replugging back in, the unit will clear the fault and begin working again. I observered what was going on and think the hi pressure fault is due to the fact that the fan blower is STOPPING but the compressor continues to run thus building up the pressure and shutting down.

I tested for voltage and see that voltage is there. 110 volts at the common and 110 volts at the red or black lead coming off the hi/lo switch going to the motor. Something I do find odd is that when I disconnect the blower motor from the circuit the voltage reading at these leads drops to around 12 volts? not sure why this is.

Anyway - the fan blower spins freely and works. It sometimes just shuts off. Sometimes when I turn the units on again after being on for a bit the blower will not even start up again, this morning the one I have not completely disassembled seems to be working.

I looked at the run caps and they seem okay, no leaking or swelling. I could not do any definitive test.

Please help - I am pretty stumped at this point... I guess I could change the run caps as a cheap guess, but I would like to understand more.

thx, Big
 
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Old 06-06-10, 07:41 AM
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The unit which is disassembled is right next to the computer her. I disconnected the compressor, but reconnected the fan blower and powered up the unit. Sure enough after some time the fan motor just stopped spinning. no clicking of relays or anything it just stopped.

After a few minutes it turned back on and is not running...

stumped. thx, Big
 
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Old 06-06-10, 08:32 AM
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actually meant to say, it turned back on and is now running... still running on high.
 
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Old 06-06-10, 08:42 AM
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A hi pressure trip is usually related to lo water flow unless we are in heat mode.

How many conductors do you have to the blower motor?
Is this a PSC or ECM motor?

It is pretty easy to measure the cap on a PSC motor...


Some meters use this symbol...



Some will have a CAP setting...

 
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Old 06-06-10, 08:48 AM
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so you don't think the fact that the fan blower turns off is what is causing the unit to shut down. if the blower is not blowing over the fins how does it convert the presurized gas back to liquid? there is only one fan blower in these units it blows the air over the fins and out into the room.

when the fan stops blowing the unit starts to ice/heat up and eventually shuts itself down?

thx, Big
 
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Old 06-06-10, 08:53 AM
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Seems like it should trip on lo pressure.
Can you measure your cap?

I'll see If I can read some literature on your McQuay. The oldest I'm finding is 2002.


http://www.mcquay.com/mcquaybiz/lite.../C_1140-11.pdf
 
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Old 06-06-10, 12:26 PM
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Hi Houston,

yes this is precisely the units I have... I have a 009 and 012, which are the 9,000 and 12,000 btu units. Mine have the Mrk IV circuit board as does these units we are looking at in the pdf.

Thanks.
 
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Old 06-06-10, 06:33 PM
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sure enough, the unit which is broken but not completely disassembled just flaked out. Unit was working all day today. So just now I was warm so I looked at the unit. compressor was plugging along, but the blower was not working. I pressume pressure was building and ultimately the unit would have shut down with a high pressure fault error reading on the led's...

anyone have some ideas. any other boards I should be posting on???
 
 

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