Split ductless heat pump conversion

mbrummal

mbrummal

Well-known member
Jan 23, 2009
2,893
22
Willow Spring, NC
I have a Air-Con 2 ton split ductless heat pump in my shop. It worked great until recently where the control board in the inside unit keeps throwing an error code (E4, Condenser Abnormal).

I've gone through the troubleshooting steps mentioned in the manual and checked the charge. The last suggestion in the manual is a bad control board. But the system is old and I don't think I value it enough to find a new one or replace it. It seems to work fine until it errors out...

So... My question is: would it be a horrible idea to bypass all of the controls on the board and use a standard house thermostat? I know I would loose the remote control (don't care) and the movement offered by the vanes but I could live with them being in a fixed position. It just sends 240v out to the compressor contactor coil and fan from the inside unit so I think I could do it with a few 24Vac relays. Any thing I'm not thinking of? Anyone else done something like this before?
 
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discostew

Well-known member
Sep 14, 2010
7,725
1,022
Northern Illinois
I have a unit kind of what your talking about. I have one made by Mitsubishi called Mr. Slim, just A/c without a heat pump. Mine is worn out. My HVAC guy says the condensing units wear out. My pressures aren't right because its worn.

As far as using the low voltage circuit of a normal house t stat. I would try it.
 
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gimebakmybulits

Well-known member
Dec 11, 2013
1,067
85
Pasadena
mbrummal

mbrummal

Well-known member
Jan 23, 2009
2,893
22
Willow Spring, NC
reading deeper into the service manual it says:

After the compressor runs five minutes, the lamp flashes 4 times per six seconds or display E4 if the temperature of indoor coil pips is more than 25℃ in the continuous 20 minutes. The controller will automatically shut down if the temperature of indoor coil pips is more than 25℃ in another continuous 20 minutes, that is the abnormality protection of outdoor units and the indicator lamp keeps its former state of flashing. If the temperature of indoor coil pips is less than 25℃ in the second 20 minutes or the compressor shuts down, the electric control board will store to the normal display and the time is restarted when starting up the compressor next time.


Translating that from chinglish I think that means if the evaporator coil doesn't get below a certain temp (25C) in 20 minutes it will flash E4 and if it doesn't cool down below 25C after another 20 minutes it will shut down. So now I'm thinking it was just too hot in my shop for it to keep up.
 
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discostew

Well-known member
Sep 14, 2010
7,725
1,022
Northern Illinois
mbrummal said:
reading deeper into the service manual it says:

After the compressor runs five minutes, the lamp flashes 4 times per six seconds or display E4 if the temperature of indoor coil pips is more than 25℃ in the continuous 20 minutes. The controller will automatically shut down if the temperature of indoor coil pips is more than 25℃ in another continuous 20 minutes, that is the abnormality protection of outdoor units and the indicator lamp keeps its former state of flashing. If the temperature of indoor coil pips is less than 25℃ in the second 20 minutes or the compressor shuts down, the electric control board will store to the normal display and the time is restarted when starting up the compressor next time.


Translating that from chinglish I think that means if the evaporator coil doesn't get below a certain temp (25C) in 20 minutes it will flash E4 and if it doesn't cool down below 25C after another 20 minutes it will shut down. So now I'm thinking it was just too hot in my shop for it to keep up.
Click to expand...

I put the system in my house when I had the old furnace that didn't have outlets in the second floor. It worked for what I wanted. But it wasn't long after that my furnace took a shit and I replaced it and got outlets and a return on the second floor. Put a regular old central air system in.

So now I'm thinking about moving that system to my garage. If I do that I'm going to get a new condensing unit cause it's lost a little cooling ability like I mentioned. When it works it does a great job.

With your problem I wonder if your dealing with the same kinda problem I am. Did you have guages on it when it was trying to cool down the shop?
 
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gimebakmybulits

Well-known member
Dec 11, 2013
1,067
85
Pasadena
Gauges on a mini split won't tell you much (other than high side pressure), check out the second link i posted for a list of potential causes for high discharge temps. Most mini split issues are dirty coils and lack of refrigerant due to leaking flare fittings. As to just replacing the condenser on an older system I'd run the numbers given the price of R-22 (most R-22 come dry) plus a new air handler will be much more efficient.
 
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Leadvagas

Well-known member
Jun 10, 2010
232
2
Leadville CO
Clean your outdoor coil, check your condenser fan, is it running?. Inspect all flare fitting for signs of leakage. Inspect the condition of condenser and evap coils, the aluminum can get pitted and loose efficiency. If there isn't anything big wrong with it, it would be worth recharging, if it's anything more than a leak you are better off going to an R-410a system.
 
mbrummal

mbrummal

Well-known member
Jan 23, 2009
2,893
22
Willow Spring, NC
I had a gauge on the low side when it was malfunctioning this weekend. It had the correct superheat but it was still erroring out. I think it was because it couldn't cool the evaporator coil enough in that 40 minute window until saturday night when it got a bit cooler.

Both of the coils are clean and everything is running like it should.
 
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Leadvagas

Well-known member
Jun 10, 2010
232
2
Leadville CO
Sounds like you have lost compressor, and or coil efficiency. If your super heat number is in range, probably a little of both. Low super heat indicates poor compressor performance or poor coil performance. Usually condenser coils that cant reject heat fast enough, high head & low super heat. If the head wont come up to over 250 psi poor compressor performance. As a general rule R-22 super heat should be 12-20 degrees corrected for elevation above 5000 feet. One other thing to check is the heating switch over valve on a heat pump, check to make sure you are not pushing hot gas into the suction side. Shows up as low super heat, low amp draw, low head and higher than expected suction. Hope this helps.
 
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gimebakmybulits

Well-known member
Dec 11, 2013
1,067
85
Pasadena
Can you post a model number? On most mini-splits there is no such thing as sub-cool and super-heat, completely different setup than a traditional split system because of TXV location.
 
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Leadvagas

Well-known member
Jun 10, 2010
232
2
Leadville CO
gimebakmybulits said:
Can you post a model number? On most mini-splits there is no such thing as sub-cool and super-heat, completely different setup than a traditional split system because of TXV location.
Click to expand...

Not really, super heat and sub cooling are the way we measure heat transfer, reguardless of metering device location or type. The difference is that on a more modern split system you get your super heat and sub cooling values from a service tool and not by direct measurement. These days I do it with a lap top, not gauges and a thermometer. If you look at Daiken, Mitsubishi, LG etc. they give specific values over time that have to be met to determine proper operation. At any rate, we're all just spit balling this thing unless one of us can actually go look at it. And I don't think my dispatcher will clear me to take a service call on the est coast.
 
mbrummal

mbrummal

Well-known member
Jan 23, 2009
2,893
22
Willow Spring, NC
Its a 410a unit and it doesn't use a TXV (at least according to the diagrams in the service manual). So superheat should work, right? Also, There is no access to a high pressure port on this one without soldering something in there so I have no idea what the pressure is on the compressor outlet.


Outdoor unit:
A13CH4H4G24Indoor unit:
A13CH4H4G24
 
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Leadvagas

Well-known member
Jun 10, 2010
232
2
Leadville CO
AHHHHHH, 410a, yes super heat will still work. What kind of values are you getting for super heat, and under what conditions (high humidity, high load, low load ?). Also if you can do it safely amp the compressor, is it pulling close to normal running amps or is it under/over. Whats kind of air flow are you getting at your evap?
 
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gimebakmybulits

Well-known member
Dec 11, 2013
1,067
85
Pasadena
(954)771-1415 Air-con's number, the guys will talk to you. He did say that after a 10 min power down if it throws the code immediately it's the board on the indoor unit.
 
mbrummal

mbrummal

Well-known member
Jan 23, 2009
2,893
22
Willow Spring, NC
Cool. It doesn't throw the code immediately after restart.

I was getting (from memory) about 28*F of superheat with 85*F condenser air temp and 73*F wet bulb evaporator entering air temp.

I think it was just overloaded and shutdown because it thought something was wrong because it wasn't cooling down.
 
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Leadvagas

Well-known member
Jun 10, 2010
232
2
Leadville CO
28 degrees is pretty high super heat. As a very general rule, you want super heat and sub cooling to be roughly equal, and lower than 20 degrees.
 
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Leadvagas

Well-known member
Jun 10, 2010
232
2
Leadville CO
Yeah, that chart should get you there. By the chart the out door temp would have to be 75 dry bulb and the indoor temp would have to be 70 wet bulb.
If both of those are true then your charge should be correct, with a super heat of 28 degrees. If both of those are not correct and you just have a super heat of 28 degrees, then the charge may not be correct. Do the 5 steps below the chart, that should give you a better idea. Also use a digital or a good contact thermometer to measure line temp, not an infrared thermometer.
 
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