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Community and Q&A

Vacuum Pump Procedure for MrCool

raul4817 | Posted in General Questions on

I’m running my lineset tomorrow weather permitting.

I’m getting hung up a bit on vacuum procedure with this particular model.

I have a mr cool universal (rebadged midea i think) and from what the manufacturer is telling me the coil and condensor are precharged. The liquid and gas valves @ the condensor and air handler are both equipped with stop valves.

So my hang up is pulling a vacuum with this setup.

Can i pull from either unit indoor or outdoor? Inside would be  way easier for me.

Here is my game plan

1)Remove  valve core from both liquid and gas valves at the air handler side.

2) pressure test both lines

3) pull a vacuum on the gas valve(3/4″ line)

4) open stop valve on gas line at the air handler.  Reinstall  valve core.

5) repeat steps 2&3 on liquid line(3/8″).

6) open stop valves on condensor.

Is this the correct methodology?

Not as pressing hard but still in the back of my mind.
The install manual calls for a 5 wire thermostat wire however the motherboard has 6 spots.
B,W1,R,C,G,Y.  the manual omits Y . Im calling the manufacturer monday on this.

Lastly I opted for an 8kwh heat kit that comes with a 45amp breaker. The blower motor calls for a min 4amp max 15amp. The wiring diagram on the unit states to omit the wiring to motherboard if using a heat kit. So my math is as follows
8000 watts/240= 33amps + 4amps.
Puts me at 37amps on a 45amp breaker. Mr cool rep says to wire the motherboard on a separate breaker but then said I could do it as the diagram states. I don’t see the need to take up more breaker spaces if not necessary. I’ve wired only the 45amp side unless someone here has a different opinion.

The manual is lacking to say the least and tech support is fair.


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  1. bfw577 | | #1

    The indoor coil is most likely filled with nitrogen at the factory and all the refrigerant is in the outside unit. That is pretty much the standard in the hvac industry. No need to open both valve cores. Just remove the larger 3/4 one and connect your vacuum pump there.

    There appears to be no input wire on terminal Y so there should be no issue omitting it.

    1. raul4817 | | #2

      I'm going to call Mr cool on Monday. If it is indeed nitrogen then I would

      Remove valve core 3/4"
      open the stop valves on the coil,
      add additional nitrogen to leak test,
      Pull vacuum,
      Open stop valve on condensor,
      Reinstall valve core,

      This can all be done from air handler gas valve correct? The condensor side valves are in a terrible spot inside the housing. No room to attach the valve core removal tool comfortably.

      This unit is has an optional no vacuum precharged linset you can purchase. hence the coil being precharged. The question is if it's with refrigerant or nitro as you say. There manual says to connect precharged lineset and open four stop valves inside and outside. If the coil is indeed nitro filled then it would in theory mix with the 410a?


  2. walta100 | | #3

    The MRCool I installed was the “DIY” unit with the “precharged” lines with screw together connections. From the sounds it made the indoor unit and line set were shipped under vacuum as I could hear the refrigerant flow into the unit when I opened the first valve.

    First point to be 100% clear do not open the valves on the outdoor unit until you are sure you have no leaks in the line set or evaporator unit and both are under a full vacuum.

    How long are you planning on leaving the lines under nitrogen pressure when testing for leaks?

    Do you have a micron gage to measure your vacuum level? No your gage set is not accurate enough.

    Do you have the correct torque wrench and flaring tools to connect the line set correctly?

    You did get the federal license to avoid someone reporting you to collect the $10k bounty from your $25k fine?

    Unless you are on a clock is a lot of trouble to remove and reinstall the valve cores and the only advantage is how fast you can evacuate the system. I say let the pump run an extra hour and skip 2 steps.


  3. raul4817 | | #4

    From what ive gathered online it seems as though the air handler is precharged with 410a. Im waiting on confirmation from Mr cool and there recommended best practices

  4. proxybox | | #5

    Raul, I'd like to ask you details about your mr cool installation. I'm going to vacuum and charge too and like your instructions. Appreciate your help

    1. raul4817 | | #6

      If I recall correctly this unit was pre charged with 410a per mr cool. Air handler and condensor both precharged.

      I ended up pulling a vacuum on each line individually then releasing refrigerant one by one.

      A little time consuming but that made the most sense. I believe I pulled each line down to about 75 microns +/-. Triple vacuum on both.


  5. proxybox | | #7

    Raul, Thanks for the response! You're the only guy on the net who I found who has done his own lineset by himself. The air handler has the 410 charge.

    1. Did you install a drier-filter?
    2. Did you add additional 410a? (standard length 24.6 feet: no charge up to ≤31.2 feet | ≤9.5m: add refrigerant at 0.32 oz/ft)
    If so, did you add .32 oz for distance past the 24.6 or 31.2 feet? Or did you do the supercool method assuming that figure is on the condenser spec label.

    Thanks Raul!

    1. raul4817 | | #8


      No I did not use a filter drier.

      My run was right around 24ft so I didn't add any extra charge. However I probably would have added after 24. I would have to read the manual again to justify my reasoning though. The manual is definatley lacking and tech support is a good resource but definatley some fuzzy details provided by Mr cool.

      One thing to note is the final bend to the condensor? It is a tricky one and I ended purchasing a Hilmor tubing bender to make it. I kinked my 1st linset using the spring type benders.


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