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John Dirks Jr

Mini split lines frosting up

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Hi folks,

I recently installed a  Mr Cool DIY mini split system.   This one    It comes with a pre charged line set.

The installation went well and the system worked fantastic for a few weeks but then the cooling performance dropped substantially.  I noticed the the high side line frosting up and a little research tells me that blockage in the line set is a likely culprit.  I removed the panel to observe the innards and ran the system to watch. 

Now, please understand that on this system, the high side line exists of two very small lines that run the distance from the evap to the condenser.  The only exception is these two tiny lines come together into a larger line at the fitting connection to the condenser unit.  Then, they split back into two tiny lines inside of the condenser body.  From there, one of the tiny lines loops back to the junction and the other goes through what looks like a small inline filter or dryer.  At the other side of this little inline thing,  the line gets larger and runs directly to the bottom of the condenser core.

In the pictures below you'll see the tiny high side line spun in a coil.  During my observations, one side of the coiled line frosts up during the heat cycle, and the other side frosts up during the cooling cycle.  This makes me think there is a blockage in this coiled portion of high side line.  

What do you think?  Blockage here or possibly something else to consider?  If it is a blockage here, is there a way to clear it up or am I left with hiring a pro to cut out and replace the blocked portion?

First pic shows frosting during heat mode.  Second picture shows frosting during cooling mode.  I'm thinking theres blockage in the tiny coiled line.  

 

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Edited by John Dirks Jr

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This is the first I've ever heard of a liquid line divided between two smaller lines, unless there is more than one indoor section to the single outdoor section.

The coiled tubing looks exactly like capillary tubes, which take the place of an expansion valve.  They will frost up in high humidity.

I'd check temperature differentials to confirm that you do indeed have a problem.

Assuming you do have an issue, the most useful diagnostic move towards isolating the issue is to put the gauges on the system and see what the pressures are.

If I were to take a guess, you either don't have an issue or you've a low refrigerant charge resulting from a refrigerant leak.

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No doubt there is a problem.  I can get a 20+ degree differential in the heat mode.  70 in 93 out.  In the cooling mode, very little temp drop, especially after the line frosts up.  And it is the high line frosting up.  Cooling diff just a few degrees at best.  

While it was working good prior to the issue, condensate would be coming out the drain line and running down the driveway in a stream.  Now, it still comes out but only in a faint trickle.  

Again, good exchange on heat cycle, poor exchange in cooling.  The head unit does not have electric backup heat so the exchange in the heat cycle suggests that maybe the refrigerant charge is ok.  But I’m not sure of that. 

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You can get a heating differential with low refrigerant charge on account of that heat coming from the compressor discharge but cooling differential depends on having enough charge to hold off expansion of the liquid until it reaches the capillary tubes.  I think that might be what's happening; the liquid is evaporating before it reaches the capillary tubes in the indoor section.

A single lo-side gauge connected to the vapor line, with the system in cool mode, might be all you need to identify a low refrigerant charge.  Charging it requires gauges.

I looked at the two photos again.  The first one shows liquid returning to the outdoor section evaporating before it even reaches the capillary tube.  It's supposed to remain liquid until it passes the tube.  The tube is the constriction device that creates the pressure differential across the compressor.  The second photo shows liquid exiting the condenser coil evaporating already, still inside the condenser section.  It's supposed to remain liquid until it arrives at the capillary tube in the indoor section.  Low refrigerant charge.

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Since the system started acting up just a few weeks after installation, the leak is likely a fast one, making it easier to find.  Go to an AC wholesaler and buy a bottle of blue soap.  It's a pump bottle, always blue in color.  Wet down every connection in the lines until you find the leak.

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Edited by Marc

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Just curious: how do you make the refrigerant line connections on a "do it yourself" heat pump?

Those lines have to hold some pretty high pressures over some pretty wide temperature swings. There's a reason why they're typically brazed. 

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Jim,  there are special fittings on the line set.  The line set is attached at the evaporator unit from the factory.  You feed the lines through the wall and lift the evap into place.  Run lines to condenser unit and attach.  The fitting has some sort of check valve that gets forced open as you tighten the nut.  

The instructions say to work quickly through the fitting connection process and that there may be some slight leakage during such.

Maybe there’s a leak like Marc suspects. Maybe I didn’t tighten the fittings enough.  I’m going to search for leaks, hopefully find them, fix them, evacuate, recharge and cross fingers.  

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I stopped trusting any connection but brazed for R 22 over 30 years ago.  It works for 134A but I sure as hell and taxes wouldn't trust it with 410A because 410 A operates at pressures higher than even 22.  Get some dish-washing soap/water and wet down them line set connections.

Edited by Marc

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I’ll do that Marc.  Meanwhile, here’s another question while we’re at it. 

Is it possible for the leak to happen only at higher pressures, such that if I check it after being shut down for a while it won’t show leakage?  But start it up, build pressure, then leaks are evident?

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1 hour ago, John Dirks Jr said:

I’ll do that Marc.  Meanwhile, here’s another question while we’re at it. 

Is it possible for the leak to happen only at higher pressures, such that if I check it after being shut down for a while it won’t show leakage?  But start it up, build pressure, then leaks are evident?

It's possible for leaks not to show up when the system is off.  Those would be the leaks that act up only under condition of line side pressures, temperatures typical for normal operation of the AC and perhaps vibration.

Edited by Marc

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2 hours ago, John Dirks Jr said:

Jim,  there are special fittings on the line set.  The line set is attached at the evaporator unit from the factory.  You feed the lines through the wall and lift the evap into place.  Run lines to condenser unit and attach.  The fitting has some sort of check valve that gets forced open as you tighten the nut.  

The instructions say to work quickly through the fitting connection process and that there may be some slight leakage during such.

Maybe there’s a leak like Marc suspects. Maybe I didn’t tighten the fittings enough.  I’m going to search for leaks, hopefully find them, fix them, evacuate, recharge and cross fingers.  

The data plate that you posted shows 550 psi. Damn!

I'd love to see a field-assembled fitting that can hold that pressure under 100-degree swings in temperature over the lifetime of the equipment. 

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I used dish washing detergent on the fittings both while shut down and in operating modes.  No signs of leaks at the fittings whatsoever.

When put in cooling mode, the frosting of the high side line happens really quick.  Like 30 seconds it begins and by one minute it’s frosted over totally.  It’s not humid at all here today.  

Are we sure there’s no chance of an internal blockage?

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Can't be sure of anything at this point, except that it's time to put the gauges on it.

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Will do.  My acquaintance with HVAC experience was here earlier but his gauge set didn’t fit the new larger 410a fitting on this unit.  I have an adapter on order and it should be here tomorrow.  

Now, if the gauge confirms the charge is still with in normal range, then would you be suspicious of a blockage?  

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Let the gauges speak first.  Give me the readings, along with indoor and outdoor temps.

The symptoms shown in the two photos don't suggest a blockage.  A blockage would have frost immediately adjacent to it.  Course, I could be wrong.

Edited by Marc

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Well, one side of that tiny coiled high line frosts in the heat cycle, and the other side in the cooling cycle.  I can duplicate over and over and it happens quickly.   Like nothing is passing through that tiny coil. 

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I see two coiled lines and the refrigerant isn't taking the same path on both photos.  One of the small tubes is used for cooling mode, the other for heating mode.

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The second coiled line you see in the back loops right back to the high side line.  

It’s like this.  There’s  larger line that comes through the case from the fitting (high side).  This line goes into a bubble like thingy.  Then the two tiny coiled lines come out of the other side of the bubble.  One of the coiled lines goes to the evap core.  The other coiled line just returns to this bubble thingy that it came from. 

So, the way I see it, both tiny coiled   lines are on the high side. Because one just comes from the high line, then returns right back to it.  

So, for any refrigerant to pass through the evap, no matter what direction or mode, it has to pass through the tiny coiled line in the foreground of the pictures.  

Edited by John Dirks Jr

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3 minutes ago, Marc said:

Could that bubble like thingy be a check valve?

 I think its purpose is simply to transition from the larger diameter portion of the high side line back into the two smaller ones, just like in the line set.  As I said before, the line set high side is comprised of two very small lines that transition into on larger line at the attachment to the evap and the fitting at the condenser.  Then,  after going through the fitting and into the condenser case, it splits back into the two smaller lines.

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7 hours ago, John Dirks Jr said:

The second coiled line you see in the back loops right back to the high side line.  

It’s like this.  There’s  larger line that comes through the case from the fitting (high side).  This line goes into a bubble like thingy.  Then the two tiny coiled lines come out of the other side of the bubble.  One of the coiled lines goes to the evap core.  The other coiled line just returns to this bubble thingy that it came from. 

So, the way I see it, both tiny coiled   lines are on the high side. Because one just comes from the high line, then returns right back to it.  

So, for any refrigerant to pass through the evap, no matter what direction or mode, it has to pass through the tiny coiled line in the foreground of the pictures.  

I made a mistake in this post.  I mentioned evap core in two places.  In both instances I meant to say condenser core.

Also, I cant believe I have not mentioned this yet but the system has built in leak detection which shows "EC" on the indoor unit display when leakage is detected.  Considering my lost performance, if refrigerant loss were the cause, that's a substantial amount of loss.  Surely enough loss to trigger the detection system to signal loss, I would think.  I've gotten no "EC" display signals.

 

 

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John, where's the reversing valve on this thing?

Is the compressor inverter-fed?

Edited by Marc

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The reversing valve is in the condenser just above the little coiled lines we’ve been discussing.   

I don’t know how to determine if the compressor is inverter-fed. 

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