Mitsubishi mini not heating

[MushCreek]

Any of you guys know anything about Mitsubishi mini-splits? My main one (12K BTU) is getting a bit old, and stopped heating the other day. I may take a shot at fixing it, if I can figure out what's wrong. If you turn it on, it may (or may not) work normally for a few minutes. Then, the louvers move up into the 'idle' position and it stops blowing, acting as if it has hit the thermostat setting. I know it's making heat, because the refrigerant lines get warm at the compressor. It's well above freezing here; I tried it at 50 F yesterday, and it still wouldn't heat for more than a couple minutes. Any ideas why it's doing this? I hesitate to call a pro out, because very few of them around here seem to have much experience with minis. Plan B would be to simply replace the thing. I have all of the HVAC equipment to do that.

 

[Yankeefarmer]

It sounds like it’s going into defrost mode. Is the outdoor unit clear of air flow obstructions?

 

[MushCreek]

Yes, nothing on the outdoor unit. No leaves/snow/plastic bags.

 

[PoorUB]

Could be anything, but I would suspect it is low on refrigerant beings it tries to run.

 

[MushCreek]

Could be. It was leaking a couple years ago, and I ran stop-leak into it and added Freon. I've been expecting it to fail the whole time.

 

[Phuckin' Jim]

How is the airflow through the indoor unit?

 

[MushCreek]

No obstructions indoors, either. If I override the automatic fan, and put it on 'high', it doesn't speed up like it used to.

 

[Phuckin' Jim]

Any faults showing up on the temperature display?
How old is the unit?

 

[MushCreek]

The unit is 8 years old. I've heard that minis are only good for 5-7 years, like a lot of things these days. This is our main unit, so it runs a lot. I'll look up in the manual and see if it's giving any error signal. It doesn't have a temperature display; just a couple of colored lights.

 

[Jackfre]

One of my Fujitsu’s is 14 yrs old and going strong. I find mini-splits, the top brands, to be very durable When installed properly. Yours wasn’t. I think your problem is you had an installation issue with the leak, gave it a shot of stop leak, which is prohibited by the manuf and added “Freon.” The stop leak may have looked like the solution, but years later I’ll bet you the leak continued at a low level and low 410a shows its problems in the heat mode when you can be operating in the 600# range. Try recovering the refrigerant, Nitrogen pressure test, evacuation, and charge with liquid to the proper critical charge. You may be able to rescue this unit.

 

[MushCreek]

That's why I hesitate to use local 'pros'. The guy that hooked mine up vacuumed it, but never did a high pressure nitrogen test. When I installed the unit in my barn, I put 500 psi on it for 24 hours. I had to re-do the flares, as it very, very slowly leaked down. The factory flares looked like they had been done with a rock.

As for the existing household unit, I can pump it down and check for leaks with high pressure. I can vacuum it down as well after leak checking. I have a lot more equipment and know-how than I did a couple years ago. The only thing I don't have is a way to remove the refrigerant from the system so I can weigh in new stuff.

I read up some more, and turned off the breaker for a while. I turned it back on. The compressor ran for a while. The lines got hot, particularly the larger one, which was almost too hot to touch at the compressor manifold. After a couple minutes, though, the compressor shut completely off (not the breaker). In checking the unit in our bedroom, the manifold didn't get nearly as hot, yet it heats the room fine. The unit in question was not blowing warm air, even after the lines got warm (hot). Seems odd to me.

 

[65ranchero]

Here is a thought.
It's not on "Auto" setting is it?

 

[Phuckin' Jim]

Could very well be low on refrigerant.

Since it does run for a short time on heat mode, I would hit all of the refrigerant connections with soapy water while it is running.

If you see ANY bubbles, I would consider the unit to be low on charge.

You could try gently tightening any leaking connections to see if you can stop the leak.

After all leaks are stopped, recover, evacuate, then weigh in the correct amount of refrigerant.

 

[MushCreek]

OK, I tried it again. It took several minutes for the compressor to do anything at all. It came on, slow. After a couple more minutes, it sped up. The manifold got up to about 140 F using a spot thermometer. It started to slow down, like it was laboring. It slowed down more, and finally went off with a 'click'. It really sounded like it was working too hard. Would low refrigerant cause that in heating mode? When it was low on refrigerant in cooling mode, it just didn't cool as well, but it ran fine.

I've been all over the system checking for leaks, but have never found any, even when it did leak down. A few years ago, I replaced the coil in the indoor unit, although we never really could see a leak. That worked for a couple years, until it leaked down again, and I put the stop-leak in it. Wherever it leaks, it's never been at the connections, or at least, not that soapy water would detect. The leaks we've had have been so slow that they're hard to find. Can these things leak somewhere else, like compressor seals?

 

[yeldogt]

Did you put dye in it .. that's normally a good way to detect.

When they are low you just get the temps close to the compressor ... not enough refrigerant to pump around ... enough to expand as all the action is outside .... not at the evap like a typical system.

Shame you have problems .... they can run for a long time. 20 years is not uncommon ... my old LG is chugging along -- although not hard use.

 

[Phuckin' Jim]

Does it have a variable speed compressor?
If not, you could put an amp clamp on one of the compressor leads, and compare it to the data plate on the compressor itself while it is laboring like that.

 

[MushCreek]

I believe it's a variable speed compressor. Normally, it never shuts off, but just slows way down once the set temperature is reached. This unit gets used a fair amount, as it's the main HVAC for our house. Probably 5 months 24/7 in the summer; 2-3 months 24/7 in the winter. Luckily, our house is very efficient. We're using a 1500 w space heater to keep it at 68 F. I shut it off over night, and on a 30 F. night, we only lose about 3 F. in 10 hours.

 

[Phuckin' Jim]

A 1500 watt heater puts out 5120 btu, so the house must be fairly well insulated!

Odd that your compressor shuts off with a distinct click. I think variable speed inverter units should just shut off without any click.

Can you grab a picture of the tag on your outdoor unit?

 

[PoorUB]

A 1500 watt heater puts out 5120 btu, so the house must be fairly well insulated!

It take a lot less to heat a house than people think!

I have said it before. but I have an 1950's rambler, 930 sqft, original insulation in the walls, like a 1" bat with some sort of paper on each side. The ceiling has been blown in with more fiberglass. I can heat the house on 24,000 BTU until -30F then I need to turn on second stage on the furnace. I have no doubt that I could heat this place on 5K BTU at 30F.

 

[MushCreek]

Our house is ICF, with R-50 cellulose in the attic. The HVAC loads are so low that I couldn't size a central system, which is why we went with minis.

 

[FredWanaker]

some compressors have a crankcase heater that must be on for many hours to a day before firing up the system if it has been allowed to get really cold. I have read that a failed crankcase heater can cause all sorts of issues if one has / needs one.

 

[LS6 Tommy]

The unit is 8 years old. I've heard that minis are only good for 5-7 years, like a lot of things these days.

Fortunately, what you heard was wrong. If you had a leak before, it's back. Don't use any more stop leak. It's garbage and does sometimes screw stuff up.

Tommy

 

[MushCreek]

The problem is finding the leak. I guess once the weather warms up a bit, I'll dig into it further.

 

[yeldogt]

There were line set leak problems with some tubing -- is the insulation white? There is a specification code for the tubing and many time the kits don't meet it.

The name brand mini's have been variable for 20+ years. The old ones has VS fans and the compressor would cycle to keep the heat exchanger at temp. In the beginning they were like small splits w/ the metering device inside.

 

[MushCreek]

No, the insulation is black.

The problem is that I've had three 'pros' out here. None did a high pressure nitrogen test. None used torque wrenches on the fittings. I do better work than they do, now that I've bought some tools and done some studying. I guess I could call out a Mitsubishi service guy, but it would probably be cheaper to just replace it. Back when I bought them, installation by a dealer was significantly more than the cost of the unit.

 

[Raisedonadeere]

OK, I tried it again. It took several minutes for the compressor to do anything at all. It came on, slow. After a couple more minutes, it sped up. The manifold got up to about 140 F using a spot thermometer. It started to slow down, like it was laboring. It slowed down more, and finally went off with a 'click'. It really sounded like it was working too hard. Would low refrigerant cause that in heating mode? When it was low on refrigerant in cooling mode, it just didn't cool as well, but it ran fine.

I've been all over the system checking for leaks, but have never found any, even when it did leak down. A few years ago, I replaced the coil in the indoor unit, although we never really could see a leak. That worked for a couple years, until it leaked down again, and I put the stop-leak in it. Wherever it leaks, it's never been at the connections, or at least, not that soapy water would detect. The leaks we've had have been so slow that they're hard to find. Can these things leak somewhere else, like compressor seals?

Just wanted to share that I have three mini's going for over three years and very pleased with the performance. The 12K bedroom one quit heating; - I added a pound of refrigerant and it started working again so I started soaping down everything I could except the coils and no bubbles and but then after a week it quit again, seemed like definitely a leak.
I decided to give up the DIY stuff and call a HVAC company. I told the tech my history. He hooked up gauges saw low refrigerant and looked a few things over then climbed up next to the wall unit and stuck his ear next to it moving around a bit. He said I think i hear a leak. He slathered the coil on one end and sure enough there were bubbles about two inches in from the end. Just a manufacturing weakness. Here I was just knowing it had something to do with my self install.

Called Mr Cool dealer (Ingrams) and told them what I had, and they sent me a whole new unit with no requirement to return the bad part or other questions asked. I had always assumed if something like that happened i was without warranty because it was not a certified install.

Find yourself a someone with good ears and give it a try. Maybe train your dog