Help With Mr Cool Universal - Failed Fusible Plug

[brianpgriset]

Recently my Mr Cool Universal 3 ton ducted split system started throwing an E3 code - low pressure protection. What was odd was the unit would throw the code immediately, even before the compressor started running. To me that suggested a large sudden leak or a bad pressure switch. Zero issues prior to this since I did the install 5 years ago. With some help from Mr Cool I confirmed the pressure switch was working fine. I called out a local HVAC tech, they hooked up gauges and confirmed no pressure. They then connected a nitrogen bottle and pressured the system to 200psi and quickly found the leak. Unbeknownst to me this system contains a fusible plug, which appears to have relieved. The small lead plug in the middle was missing and gas was coming out the port. I suspect this plug is for the same purpose as other fusible plugs I am familiar with - to relieve gas pressure in the event of a fire. Not for over pressure protection. In addition the unit has a high pressure cutoff switch which has never triggered and the unit has never had refrigerant added, only the factory charge, again with five years of perfect operation.

When I showed this to the Mr Cool support they said they have seen this on a few units in the Deep South where it gets very hot. They are going to send a new plug under warranty, but that isn’t the issue so much as the 10lbs of R410a that was released.

Per the Mr Cool tech support the fix is straight forward. Replace the plug (it’s threaded). Pressure test with N2 and confirm no leak at the replaced plug. Evacuate the system and recharge with the correct weight of R410a (9.85lbs).

My questions and concerns:
- my original plan was to replace the plug myself and call a local HVAC contractor to pressure test and evacuate/charge the system. I’ve called two local vendors and both want ~$1000 to do this which is frustratingly high, considering 410a looks like it costs $10-$12 per pound. I would like to get the vac pump and gauges and do it myself, along with taking the EPA608 certification (seemed pretty easy and I almost passed on a practice test with zero prep). Would this be a reasonable path?

I’m also a bit concerned the system has been “open” to the atmosphere for awhile now (About 10 days, albeit through the very smal fusible plug port). Won’t moisture contaminate the system? My concern is if I hire someone they will do a quick evacuation of th system and not really take the time to draw a deep vacuum and make sure all the moisture is removed. Thats part of my motivation to do it myself, but I’m also worried I might mess something else up.

Input welcome. Oh and depending on the threads of the fusible plug, I might just get rid of it and put a regular plug its place. I do not want to be doing this again in 5 more years.

 

[fitter30]

Just because you can buy refrigerate or a part for X amount there is markup, labor and service call. Also have the nitrogen, a scale and vacuum pump. Most hvac companies charge by a flat rate book. Time and material charging is about gone for residential. Most minis have a split condenser coil where the two coils are in configuration front to back like slices of bread. The inner catches all the dirt and coils have to be split to clean them properly. Can only split them about 80-85%.
You tube should have videos.
Also check the operation of the high pressure switch.

 

[bonneyman]

Not a good situation by any standard.

When a fusible plug blows it's not just the freon, but the oil, too. Air and moisture infiltration can occur as well. The system needs a thorough flushing, new filter driers, oil charge added then evac and freon charge. Not a quick one-and-done.

 

[brianpgriset]

That’s part of what I’m worried about. I’ve asked the local HVAC company for scope of work for a system that went flat to see what they recommend. It’s not obvious to me where the inline filter drier is on this unit. Also Mr Cool technical mentioned nothing about this, only to replace the plug, evac, and charge. I hope it’s not the case, but I wonder if they are trying to dodge the replacement filter dryer.

 

[bonneyman]

That’s part of what I’m worried about. I’ve asked the local HVAC company for scope of work for a system that went flat to see what they recommend. It’s not obvious to me where the inline filter drier is on this unit. Also Mr Cool technical mentioned nothing about this, only to replace the plug, evac, and charge. I hope it’s not the case, but I wonder if they are trying to dodge the replacement filter dryer.

Possible. This problem is obviously not a defective fusible link, as they told you some units all over the deep SE have blown it "because it's hot". Uh, aren't A/C's supposed to run when it's hot? What troubleshooting did the guy do to determine the underlying issue? A fusible plug blows on high temp - not high pressure. High discharge temperatures can destroy the oil (depending on what type of oil that was in the system). Any burned/overheated oil residue must be removed. Plus, what damage was done to the comp while the oil was getting hot BEFORE the plug blew? A new filter/drier is a must to save the comp. Sounds like they're giving you a new fusible plug as a way to cover their arses.

 

[brianpgriset]

The fusible link is rated to blow at 70C/158F according to the writing on the plug, which seems pretty low. As such I am not convinced that there is some other underlying problem. I wouldn't be terribly surprised if it could get close to that temp inside the compressor casing during a hot SE Texas summer day. At this point I think its at least credible the fusible plug operated as designed. That said, the design is not great in my opinion.

At this point I think the only reasonable course of action is to get the new plug. I will install the new plug, but will be defeating it by putting epoxy on the outside or some other means. I've asked Mr. Cool tech support about the filter dryer, we will see what they say. After the plug is replaced I'll have the local HVAC company to as much as practical to clean the unit (triple evac, replace filter dryer if possible, etc..) and recharge. It's a gamble but it's probably the best balance of cost and longevity of the unit.

Overall this is pretty disappointing. I new i was taking a gamble getting this DIY unit. Looks like I may have lost out. Just sad it had appears, at least to this point, to have been over a $10 part.

 

[mm08822]

If this is still under warranty, can't you ask Mr. Cool for an authorized servicer and require a performance guarantee for their rep's work? Is any labor covered in the remaining warrantee period? The fusible plug is peanuts in terms of cost to get this back online.

If you were to do this work yourself, after purchasing all of the equipment and consumables, I would think you easily reach $1,000. For certain you will own the outcome of each and every step until finished - whether successful or not each step of the way.

 

[bonneyman]

The fusible link is rated to blow at 70C/158F according to the writing on the plug, which seems pretty low. As such I am not convinced that there is some other underlying problem. I wouldn't be terribly surprised if it could get close to that temp inside the compressor casing during a hot SE Texas summer day. At this point I think its at least credible the fusible plug operated as designed. That said, the design is not great in my opinion.

Yeah, that temp does seem low. Temperatures on the discharge line in an R-22 unit could get to 275 deg on a hot summer day. I didn't work on enough R-410a units to have established a baseline. But 158 deg seems low.

 

[bluedog225]

And another warranty that’s not all that helpful.

Parts only.

We’ve just come to accept it.

 

[brianpgriset]

That’s correct. Parts only. At this point I’m going to get what I can out of it and move on. Very frustrating as the unit worked great and it was this simple $5 part that caused all this.

 

[mm08822]

That’s correct. Parts only. At this point I’m going to get what I can out of it and move on. Very frustrating as the unit worked great and it was this simple $5 part that caused all this.

That's an almost useless warranty agreed.

See if you can get more parts then....dryer, lineset, compressor. Blame it on the oil breaking down attacking copper lines and motor insulation life. It's a stretch but until you try..............

 

[brianpgriset]

$1800 for evac and recharge.