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JoeFL77 05-12-2008 12:11 PM

Low Pressure Cutout?
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I have a 25 yr old MarvAir 2 1/2 ton water to air air conditioner in my attic. The compressor turns on OK. It runs for about 10 seconds until the low side pressure drops below 35 psi. The high side is about 210. If I hold the contactor closed, it is about 25 low side and 210 high side.

Does any one know the approximate pressures it should be running at? Could the low side cutoff switch be bad?

We use it rarely, but I realy could use one more season.


8 Ball 05-17-2008 05:28 AM

Your low press. switch is doing what it is supposed to do.

1.- Make sure the fan is running.
2.- check your filters
3.- May need to add refrigerant
4.- Restriction in refrigerant piping (look for frost on tubing)

5.- Do not allow unit to run for very long ( could freeze and break)
Suction should be above 65psi (depending on ambient temp) Head press. should be 225psi / 250psi, depending on water temp and flow rate.

JoeFL77 05-21-2008 08:42 AM

Dear 8 Ball,

Thanks for the info. I added some refrigerant to bring the suction to 65 and the high side is about 280. It has been working for about a week. Tomorrow I'm getting a Amana 4 ton heat pump installed. I can't wait. I've been nursing this system for 17 years.
Thanks for helping get though this!:thumbup:

biggles 05-24-2008 08:17 PM

you solved the LP now your approching the HP trip with that head at 280PSI...your condenser is fouled with something is that city water on there,that original head of 210 was right on for water cooled in the middle of the have a restiction feel the LL dryer on both sides during the run if it is cool going to the evap coil your dryer is restricted...but for now your over are the rounds on the squirrel cage and the evap coil

JoeFL77 05-26-2008 08:16 PM

Dear Biggles,

It was well water so it probably was resticted. I replace the system so it is in the A/C grave yard. I kind of miss it. I had it for 17 years. Thanks for the help. It was very nice of you to help.

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