Question about Mastercool 67680 Evaporative Cooler Air Conditioner

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My Mastercool cooler with a MC thermostat does not shut off nor does the control for high and low speed work. Is the thermostat defective? I've had it a few years.

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Posted on Jan 02, 2017

  • 4 Answers

SOURCE: I have a Mastercool 2 speed 1Hp 220 volt cooler

Go manual turn switch, sounds like an overload problem. I have a Mastercool unit and going on 12 years with same motor.

Posted on May 10, 2010

  • 587 Answers

SOURCE: high speed does not work but low speed does

If your motor only works on low speed and not on high speed first check to see if you have the proper voltage to high speed. Check with a voltmeter or multimeter, check from common on the motor to high speed on the motor at the switch. If you have the proper voltage then you have an open winding on high speed and the motor needs replaced. If you don’t have the proper voltage or any volts, then the switch is bad and needs replaced. This also will be the same if, medium speed won’t work and low speed does.

Posted on May 30, 2010

Testimonial: "great answer - I'll check it today"

SOURCE: I have a White Rogers 8A18Z-2 for my Evap cooler.

ya its open for the low speed it will not sto till u switch off the mwchine no probs u can enjoy it happyli

Posted on Apr 20, 2011

Testimonial: "Thanks for the quick answer. I thought that was the case but nice to have confirmation."

  • 413 Answers

SOURCE: My Mastercool motor hums when

It more than likely has the bearing or bushings worn. Usually better just to take the motor out and get a new one unless there is a place that can replace bearings nearby. This kind of repairman is very few and far between.

Posted on May 11, 2011

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Mastercool plus 6500 thermostat problem


Posted also on the Cooler quick cycling problem:
My Master Stat Controller (CC2000A Rev 2003) was in 2 parts. The Thermostat unit in the house and the Power Control unit in the Cooler. The power Control unit was mounted on the squirrel cage fan housing so it vibrated some when running. That means the components vibrated slightly with respect to the PC board. Especially the larger components. My first symptom - Intermittent failure to turn the water pump on. I could see a faint crack in the solder around the pin of a relay on the PC board. Re soldering the PC pins solved that problem. Later, the second symptom was quicker than usual on-off cycling of the fan. I re-soldered all the pins on the PC board and all problems subsided. A better mounting place for the Power Control Unit would be good, but outside of the cooler might be a thermal problem here in the hot desert south west.

Apr 24, 2012 | Mastercool 67471 Evaporative Cooler Air...

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I have a MasterCool II MC63/64B and the thermostat has gone out. Since MasterCool is out of business, what model/brand would I replace it with.


If you are just running the evaporative cooler any single stage thermostat will suffice. You can buy them at OSH, Home Depot or Lowe's and probably Ace Hardware.

Aug 03, 2011 | Mastercool 67680 Evaporative Cooler Air...

1 Answer

Can i install a time temp. type defrost control instead of the demand defrost type in the above unit? also i see no reason for the fan control board (low to High speed) since the fan motor does not call...


Defrost timer might be more reliable here in NY I set them @ 45minutes..The fan speed is out side tempature (ambient) selected ,low speed, running when its cooler out but you still use cooling.HIGH speed being the default speed.High/low during spring and low all winter.If your new motor is only one speed power it direct from the contactor

Jun 07, 2011 | Heating & Cooling

1 Answer

High speed does not work but low speed does. Is there an easy fix, or will this require a motor replacement to get both speeds working again? The cooler is a Mastercool model MC64C


If your motor only works on low speed and not on high speed first check to see if you have the proper voltage to high speed. Check with a voltmeter or multimeter, check from common on the motor to high speed on the motor at the switch. If you have the proper voltage then you have an open winding on high speed and the motor needs replaced. If you don’t have the proper voltage or any volts, then the switch is bad and needs replaced. This also will be the same if, medium speed won’t work and low speed does.

May 29, 2010 | Mastercool 67680 Evaporative Cooler Air...

1 Answer

Motor does not go from low speed to high speed If the motor is set to low speed it does not turn on until the high speed range is hit then it tries to go from stop to high speed and throws thw belt


MOST OF THE TIME IT IS THE DIGITAL THERMOSTAT OR LOOSE TERMINAL AT THERM. THESE STATS ARE TRICKY TO CHECK. LIKE WHITE ROGERS 4 WIRES CONTROL WITH A RED WIRE TO GREEN YOU GET PUMP WHITE YOU GET LOW YELLOW YOU GET HIGH AND SO FORTH. MASTER COOL DOES IT DIFFERENT SO YOU BUY THEIR TSTAT

Apr 21, 2010 | Mastercool 67680 Evaporative Cooler Air...

1 Answer

The Mastercool cooler is not cooling. It is only


Can you see if water is on the pad?If it is the humidity level outside might be too high,above 15-20%. the dont work too well.good luck.

Jul 11, 2009 | Speed Port-A-Cool 16" Evaporative Cooler...

1 Answer

No low speed on my mobile master cooler module no mmb12c


Could be as simple as the switch, could be as complex as a pole burned out on the motor. If you reverse the connections on the speed selector switch and you end up with low speed and no high speed then you know it's just an inexpensive switch.

May 30, 2009 | Cfm 2000 Swamp Air Cooler MMB10 MasterCool...

1 Answer

Low voltage wires


I just tested a mastercool control box and found these 4 control wire colors:

Red (24v supply)
White (pump)
Green (low blower)
Yellow (high blower)

The yellow acted as a common for testing when the blower was not on high.

Blower on low just green has 24v.
Blower on high green and yellow have 24v.

If there was a fifth wire added hopefully it would be a ground wire.

There was also the low gauge wires that were black, white, and ground that were not control wires and delivered power to the control box.

May 05, 2009 | Mastercool 67680 Evaporative Cooler Air...

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