Mini Split Not Blowing Cold Air (MR COOL DIY)

In this article, I show you how to troubleshoot a MR COOL DIY mini split not blowing cold air.

Tools I Used



First, I installed a MRCOOL DIY Ductless Mini Split (MRCOOL model: DIY-18-HP-230A) in my home office about 10 months ago. 

Also, I installed the same unit in my workshop – view blog post and video here.

These 2 units worked great during the winter and spring.


MRCOOL DIY Mini Split Problems

My DIY mini split stopped blowing cold air in May of 2017, so I notified MRCOOL via email of my problem.  

The folks at MRCOOL were very responsive and we traded a few emails regarding troubleshooting tips and results.

Unfortunately, we were not successful in resolving my issue.

Consequently, MRCOOL informed me I would need to call a certified HVAC professional and have them check my unit.

How to Install a Ductless Mini Split - Part 2 - Intro


Low Refrigerant

The HVAC professional tested my unit and determined my DIY ductless mini split was low on refrigerant.  

After spending roughly 30 minutes checking for a refrigerant leak, he could not find a leak.  The HVAC technician and I came to the conclusion my MRCOOL mini split was not properly pre-charged from the factory.  

Or, refrigerant was lost during the installation. Either way, my ductless mini split needed more refrigerant.  

As a result, he added more refrigerant and my mini split began cooling again.


Second HVAC Service Call

My MRCOOL mini split stopped blowing cold air again in August.  

I didn’t spend much time in my home office in June and July, so it is quite possible it stopped cooling in June or July. 

In turn, I did not call MRCOOL for this issue; rather, I called my HVAC professional again.

The HVAC professional put his gauges on my mini split and explained my unit was in a ‘vacuum’.  

This means the unit has no refrigerant whatsoever.

So, it was obvious now my mini split definitely had a leak.  

After he recharged the unit with refrigerant, he spent over an hour taking apart my ductless mini split (outside and inside unit) to locate the leak.

Despite his best efforts, he could not find the leak.


MRCOOL Warranty Claim

I found the original email chain I sent to MRCOOL in May and used it to notify them of my updated issue.  

In turn, they responded immediately and asked for additional information from the unit.  

Once I provided them with the serial numbers, receipt, and a few other items – they shipped a new inside unit and line set.  

In addition, the unit arrived at my home 2 days later.


Troubleshooting Process

I was definitely irritated I had to pay an HVAC professional to diagnose my MRCOOL ductless mini split issue on two separate occasions.  

Furthermore, my irritation increased considering my unit was under warranty and less than a year old.

After thinking about the situation from MRCOOL’s perspective, I began to understand why it is not feasible for MRCOOL to have technicians spread throughout the country to diagnose warranty issues.  

Essentially, these units are roughly half the cost of the similar units.  

Furthermore, it is not possible for MRCOOL to sell their DIY mini splits at such an affordable price and pay technicians throughout the country for maintenance issues.  

Ultimately, the technicians would significantly raise MRCOOL’s operating costs.  

The increased operating cost rolls downhill to the consumer in order for MRCOOL to remain profitable and stay in business.


Traditional Mini Split Cost vs DIY Mini Split Cost

Obviously, balance exists with everything and mini splits are no different.  

First, a conventional DIY mini split costs approximately $3800.00 with a full warranty, which includes diagnosis and troubleshooting.  

The MRCOOL DIY Ductless Mini Split of similar size is $1,450.00 with a factory warranty.  Normally, not as comprehensive as the traditional system.  

In other words, pick your poison.

Now, on to the steps I took to install my mini split I received as a result of my warranty claim.


Remove Mini Split Covers

The unit on the right is for my home office and the unit on the left is for my workshop – view video and detailed instructions here.  

First, I removed the top cover and disconnected the electrical line that connects to the inside unit.  

Next, I removed the bottom cover and placed it to the side.

How to Install a Ductless Mini Split - Part 2 - 2


Close Refrigerant Valve

First, it is important to close the refrigerant valves with a hex wrench. 

Essentially, this will prevent the refrigerant from escaping when the lines are disconnected in the next step.  

Next, I remove the nut that protected the valves. 

Then, I tightened the top valve and then the bottom valve.

I take pictures when I work on things I am unfamiliar with.  

Ultimately, this helps me remember how to reassemble things.


Prepare Refrigerant Bundle

I’m not a fan of heights, which is ironic considering I am 6’7″ tall.  

First, I had to release the drain hose & cut out the spray foam in order to pull the refrigerant bundle back through.

Furthermore, the drain hose for my MRCOOL DIY Ductless Mini Split was secured to the refrigerant bundle with tie straps.  

Additionally, I had to cut away the spray foam that sealed the hole for the refrigerant bundle.

It doesn’t look high, but it certainly is higher than it looks.

How to Install a Ductless Mini Split - Part 2 - 7



Remove Inside Unit from Wall

First, I disconnected the drain hose from the inside unit of my mini split.

MRCOOL DIY Ductless Mini Split - Remove Plug - 9


Once the drain hose was disconnected, I pulled a bit of slack inside from the refrigerant bundle.  

Next, I slowly lifted the inside unit from the wall bracket and gently laid it on the ground.

MRCOOL DIY Ductless Mini Split - Lift Mini Split - 10



Pull Refrigerant Bundle

First, I slowly pulled the refrigerant bundle through the wall.  

Obviously, this job requires 2 people.


Improve Mini Split Cosmetics

Most mini split installs are very straightforward.  However, mine is a bit different and more complex.

FIrst, this DIY ductless mini split is upstairs in my workshop. 

Also, the wall the inside unit is mounted on is not an exterior wall.

Furthermore, my staircase is behind this wall.

As a result, the refrigerant bundle has to pass through this 4 foot space to get to the exterior wall.

Since my home office has a maritime/marine theme, I built a box with a ship bell to hide the 3″ PVC pipe that houses the refrigerant bundle.


I also decided to purchase a toilet floor flange (not sure the proper name) to improve the look of the PVC wall plate that comes with the unit.  

It actually fits nicely with the theme of the room

MRCOOL DIY Ductless Mini Split - Toilet Flange - 13


Unbox new Mini Split Wall Unit

I unboxed the new MRCOOL DIY Ductless Mini Split.  

Instead of replacing my remote control mount and reconfiguring my WiFi, I transferred them from my old unit to my new unit.


Hang New Mini Split Wall Unit

Next, I pushed the refrigerant bundle through the hole in the wall to the exterior wall as far as I could while the mini split was on the floor.  

Then, I placed the new DIY ductless mini split on the top of my ladder and strapped it down so it would not fall.  

Quick Tip:  Ask someone to help you because it makes things much easier.

While the mini split was on the ladder, I pushed more refrigerant bundle slack through the wall.  

I mounted the new mini split on the existing wall bracket.

Also, I forgot about the drain hose.

In turn, I had to get my cable fish stick, tape the drain hose to the end and push it through to the exterior wall.


Connect Mini Split Refrigerant Lines and Drain Hose

While I was on my ladder to retrieve the drain hose and straighten the refrigerant pipes, I heard a horse behind me. 

So, I turned around and saw a horse at the back of my fence fussing at me.

Moreover, I completely forgot my neighbor has a few horses on their 10 acre property.

Next, I reconnected the refrigerant lines to the outdoor condenser unit on my MRCOOL DIY Ductless Mini Split.  

If you would like to learn how to do this, checkout my post on how to install a DIY Ductless Mini Split.


Final Mini Split Not Cooling Test

First, I performed a final test on the unit and everything worked well.

My mini split obviously has refrigerant in it because it is cooling.

Also, I’m sure I lost some since the HVAC professional refilled it.  

Ultimately, I plan on calling him back one more time to come check the levels.

MRCOOL DIY Ductless Mini Split - Final Test - 22



Obviously, this was not an ideal situation.  Equipment & electronics fail – it happens.

However, I’m happy with the support from MRCOOL.

MRCOOL fixed the issue and responded to my issue.

Ultimately, that is all anyone can ask for.

NOTE:  MRCOOL did not pay me nor did they send me anything for free in exchange for this video or blog post.  


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In this article, I show you how to troubleshoot a mini split not blowing cold air from MRCOOL.  I filed a MRCOOL warranty claim and replaced my mini split blowing cold air.
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2019-07-18T11:41:51-05:0010 Comments


  1. Steve Hess March 18, 2018 at 1:36 am - Reply

    I subscribed, going to install my unit on my next days off. Wish me luck, I have to go through 3 walls.

    • Jeremy March 18, 2018 at 11:24 am - Reply

      Hi Steve, good luck on your project! Feel free to contact me if you have questions. I really appreciate you visiting my website and reading this post.

  2. Dan Casey March 31, 2018 at 6:20 pm - Reply

    Hey just wanted to say great job on both install videos of the Mr cool units ! And then the warranty claim video too…I just finished installing the diy mr cool 24 k unit seems good so far but like you come August here in central Florida will be the…
    I do have a question …on my unit the fan keeps running on the indoor unit even after the compressor (outdoor) stops running ….do yours do this also ?

    Also great web site you have too…enjoyed looking around….thanks and have a good one…

    • Jeremy March 31, 2018 at 11:18 pm - Reply

      Hi Dan, thanks for the compliments and perusing my website!
      To answer your question: Yes, this is normal operation of mini splits. The indoor fan will run all the time unless you turn the unit to off. The temperature sensor is in the indoor unit not the remote or thermostat. The fan keeps running to sense the temperature. It uses very minimal electricity when running the inside unit only.
      I was worried about this as well and, after speaking with numerous hvac professionals, learned this is normal behavior.
      Thanks again for visiting.

      • Mark Gerace May 18, 2018 at 11:23 am - Reply

        Jeremy, great video. I just started to install my Mrcool system and since you seem very knowledgeable maybe you can answer a question. In the installation manual step 5 it explains about connecting the drain hose. No problem there but it has highlighted 2 sentences that say Plug the Unused Drain Hole “to prevent leaks you must plug the excess space in the drain hole with the rubber plug”. Not really understanding what they are talking about and in not one install video do I see anyone doing this. Any help would be greatly appreciated.

  3. Jon L April 14, 2018 at 1:59 pm - Reply

    Thanks for putting together this write up, extremely through and balanced on your commentary. Very much appreciated!

    • Jeremy April 19, 2018 at 7:34 am - Reply

      Jon, I really appreciate your message. I also hope my blog post provided you with value. Don’t hesitate to reach out to me for help!!!

  4. Jeff Combs November 30, 2018 at 8:51 pm - Reply

    Unit is not blowing cold air is it able to have freon added? And when I turn heat on it won’t work at all and unit is alittle over 2 years old. Suggestions please.

  5. TrTri-Tech Air Conditioning May 17, 2019 at 12:30 am - Reply

    Split system air conditioners use a quirk in the laws of physics to cool indoor air: namely, the tendency for liquid to absorb heat when it transforms from liquid to gas or vapour!

  6. Gary Ruprecht July 3, 2019 at 11:02 pm - Reply

    on the 18000 split I just bought it says to keep the back of the unit at least 10 inc from the wall it needs to cool proper to work the reason you might have trouble with the one and not the one in the work shop the work shop one don,t have a far to go so so don,t need as much cooling ,,,that one in your upstairs have father to travel so needs more cooling causeing the unit to over heat

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