Question about Mitsubishi MSM18NW Air Conditioner

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I have a hot and cold system when in heat mode only cold air is emitted and after a short while the mains trip

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Hi,
Here is a tip about Mitsubishi Air Conditioners and how to get the manuals for all of the mitsubishi line. The manual include both troubleshooting and installation.

Mitsubishi Air Conditioner Troubleshooting and Repair
http://www.fixya.com/support/r5643983-mitsubishi_air_conditioner

heatman101

Posted on Aug 22, 2010

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Why after a loud bang did breaker trip on ac/heat unit. Wont run at all now


If its a heat pump and the compressor was running, there is a possibility that the compressor itself or something IN the compressor circuit shorted out and tripped the main breaker. It could also be something as simple as a shorted compressor run capacitor.

If its a forced air system with an electric air handler, resistance heat and central air conditioning....it could be just a shorted heating element that tripped a breaker OR it could have been a control circuit short that blew out the non-fused control transformer.

There are only about fifty scenarios that could have happened to cause the noise and to cause the systems failure....but these are the first few basics that could easily be investigated.

Apr 14, 2015 | Heating & Cooling

Tip

Why your unit is freezing up.


To understand why your AC or heat pump is freezing up, it helps to know how your system works.

There are 7 major parts to an AC system, 9 with a heat pump.

1 - Condenser/heat pump (The outdoor unit)
2 - Air Handler (the indoor unit unless the system is a package unit, then all is outside in one system. The air handler is usually found under the home, in an attic, or in a closet.)

In the condenser are the following major parts.

3 - Compressor
4 - Condenser coil
5 - Condenser fan
6 - (HPs only) reversing valve

In the air handler are the following major parts.

7 - Blower motor
8 - Evaporator coil
9 - (HPs only) electric heat strips

Some systems known as "dual fuel systems" use another heat source in place of the heat strips, usually a gas furnace. I will address gas furnaces in another post.

When an air conditioner is operating properly several things are taking place.

1 - The compressor is compressing or "pumping" refrigerant through the system.

2 - through changes in pressure, the refrigerant makes the evaporator coil get very cold, and the condenser coil gets very hot.

3 - The blower motor/fan circulates air across the evaporator coils, as the room temperature air (Also known as "indoor ambient") goes through the cold coil, it exits, cooled approximately 15 to 20 degrees cooler than when it entered. (In a ducted system, the blower is also the fan that circulates the air throughout the home.)

4 - The condenser fan circulates air across the condenser coils. As the outdoor air goes through the condenser coil, it removes heat from the coils that are very hot. This in turn removes heat from the refrigerant so it can run its cycle again, and through pressure changes, cool the evap coil.

5 - With a heat pump, the reversing valve reverses the flow of refrigerant in the condenser and evaporator coils.
In AC mode, the evaporator coils get cold, and the condenser coils get hot. But in heat mode, the evaporator gets very hot, and the condenser very cold.

Now, whichever coil is getting cold will freeze up if there is inadequate air flow across the coil, as the refrigerant in it is far below freezing, and there is not enough airflow to keep the humidity in the air from freezing on the coil.

Things that can cause poor airflow are,

1 - Dirty/clogged coils
2 - dirty/clogged filter (will only effect evaporator coil)
3 - Closed/blocked vents (will only effect evaporator coil)
4 - Malfunctioning or dirty fan

Low refrigerant will also cause a coil to freeze up, reduce efficiency and cause the system to run for long periods of time. Not to mention, shortening the life of the unit.

With a heat pump, in heat mode only, the condenser (outdoor) coil will routinely begin to freeze up in cold temperatures. This is due to the fact that the refrigerant is below freezing, and the cold outdoor ambient temp is not warm enough to keep the condensation in the air from freezing on the coil.

Note, a properly working AC should never freeze up.

A heat pump is equipped with defrost controls to prevent ice buildup.
Some are controlled by timers, some by temp.

When a HP is going into defrost mode, the condenser fan shuts down, the reversing valve reverses the flow of refrigerant and the once cold condenser coil now gets very hot, defrosting the coil. (Many people have said this process sounds like the unit is coming apart, or about to explode and are frightened by the "smoke" which is really just steam from melting ice that comes off the unit.)

During defrost mode, the secondary or "auxiliary" heat comes on to ensure that you are still getting warm air from the vents. (Again, this can be electric heat strips or a dual fuel system)

If you are experiencing cold air from the vents during defrost, that means your auxiliary heat is malfunctioning.

The auxiliary heat is used for three purposes.

1 - during defrost mode to maintain warm airflow (automatic)
2 - when the HP cannot maintain the set temp due to extreme outdoor temps. It comes on when the indoor temp drops several degrees below the set temp on the thermostat (automatic)
3 - For emergency heat source when the HP is not working. (Manual)

To recap....

Iced up coils?

Poor airflow
low refrigerant
Malfunctioning fan
failing defrost system


There are two things that can be done in a pinch to help de-ice frozen coils. This may get you by until the repairman can get there, or you can fix the system if you are a do-it-yourselfer.

HPs frozen outdoor coil in heat mode, not going into defrost?

Cover most of the vents, and turn the system onto cooling mode until the outdoor coil is thawed. then uncover vents and return to heat, or emergency heat. (this usually takes 15 min or less)

Frozen coils in AC mode with a heat pump?
Turn the system to heat with the thermostat on just high enough to get the system to come on. (again, usually takes 15 min or less to thaw.)

AC only, with frozen evap coils? (this can sometimes be seen frozen all the way outside to the compressor on the copper lines.)

Turn the system off, and the fan switch from "auto" to on".
This will usually defrost the coils within 1 to 2 hours.
(If your system has the furnace in line before the evap coil, turn the system to heat, and the furnace will defrost the coil within minutes.)



on Dec 25, 2008 | Carrier XHB123D X/Y Series Heat/Cool Air...

1 Answer

Bought an upright Frigidaire Freezer on Craigslist and the inside gets cold and works like a champ but the outside side panels get very hot- is this normal or is there a short?


If there is a short circuit, the circuit breaker protection in your house wiring would trip (Open the electrical circuit path).

It is normal for the condenser, which is on the outside of the appliance to be hot because it is transfering the heat from inside the freezer cabinet to the ambient air outside the cabinet. Make sure that you give the appliance enough space all around the hot condenser so that it can transfer its heat to the surrounding air efficiently.

P.S. Some freezer designs integrate the condenser coils into the metal cabinet, thus the hot side panels.

Aug 28, 2011 | Frigidaire 14 cu. ft. / 396 liter Upright...

2 Answers

DONT KNOW WHAT SIMBLES ON REMOTE CONTROL ARE EG HOT COLD ETC


Symbols:
1. fan leaves - Fan only
2. Rain drop- Dry mode
3. Snow flake-Cool mode
4. Sun- Heat
5. A or AU- Auto mode.

Mar 20, 2011 | Mitsubishi MSZ09UN Air Conditioner

1 Answer

Fan doesnt work on heat cool ok


Often the fan will cycle on and off on the heat mode. A cold air prevention mode is often built into modern Ac units whereby the indoor fan wont turn on until the internal system pressure is up to a certain point and heat is available to pump into the room. If the system cant come up to pressure or temperature then possibly the system is low on gas. Place your hand on the large pipe leaving the outdoor unit, it should be HOT when the system is on heating mode and running. If not Hot, then it is low on gas.

Feb 24, 2011 | Pace 18HPEWHEC Split System Air...

1 Answer

Heater shut down sometime in the middle of the night and now it will not turn on. I checked the breaker box and when I flipped the master switch, it came on for about a minute or two but was blowing cold...


Hi what has happened is, this is a heat pump. The main breaker keeps tripping because the compressor is shorted. I hate to give you this news, but anytime a unit keeps tripping the main breaker on a heat pump, the compressor is either locked up and drawing enough amps to trip the breaker, or it is shorted internally. This is something that you will have to call a tech out on. I am sorry to give you this news, but this is all it could be. If it came on for a minute blowing cold air, the compressor wasn't running due to it being shorted out. This is your only choice is to call someone out to check it. If this is a older unit, you may be better off replacing the outdoor unit. If not, get an estimate on a compressor change out. I wish you all the best on this, and I know this is bad news, but these things always happen at the wrong time of year. Please keep me posted.
Sincerely,
Shastalaker7
A/C, & Heating Contractor.

Dec 28, 2010 | Carrier 38CKC042 Air Conditioner

1 Answer

Air conditioner is blowing hot air, it was installed 1995 , the top switch option is CONT FAN AUTO and bottom switch is HEAT OFF COOL and on the right is a dial from 10-30


First of all, what do you mean by hot air? DO YOU REALLY MEAN ROOM TEMERATURE AIR THAT JUST DOES NOT FEEL COLD? If this is a heat pump system, we need to look at it differently than if it is a gas or oil fired heater. Next, the thermostat control that says "cont.fan auto"----- this actually means FAN switch to be in AUTOMATIC RUN or CONTINUOUS RUN mode. Leave it in auto mode and forget that it is there; this little switch confuses a lot of people. The dial that says 10-30 is centegrade temperature that translates to 50-87 degrees farenheit. In order to get air conditioned (cold) air, you must have thermostat fan switch on auto, the heat/off/cool switch on cool, and the 10-30 dial on 20 or 21 (68-70 f.) assuming the room temp is at least 72 degrees f. or higher. If you still do not get cold air, then there is a problem with the cooling circulation system which can be tripped circuit breaker to outside compressor unit, loss of freon refrigerant, bad control such as relay or reversing valve in outside unit, stuck heat sequencers or heat element relay that are giving you heat at the same time giving cold if it is a heatpump system. You will need a skilled service person to determine these problems. Goodluck, Macgivor

Nov 09, 2009 | Cell Phones

1 Answer

The fuse for the gauges keep blowing and also when heat is turned on cold air comes out the bottom but when it is in defrost mode its hot


disconnect the main plug from your instrument panel...does the fuse blow...if it doesnt, check wiring on the cluster panel, a wire could be rubbing causing a short.
you could have a line that feel off on the heater core or somewhere else ..sorry i cant help more. tell me does your air conditioning work when you turn it to full hot?

Sep 30, 2009 | 1993 Jeep Wrangler

1 Answer

Ac and heater work great but go off. Then Ac blows Hot / heater cold air


I got a bigger coat to wear! while I find time to look into it further. I appreciate knowing there is more help available and will try the Primo Asist plan later. thank you louie

Nov 03, 2008 | 2001 Honda Insight

1 Answer

I have a Ruud deluxe 80 plus heater. The unit is running, the pilot light is lit, still no heat.


repost with more specific . motor aka fan is running?stat is set to heat and max heat? how old? general progression is as follows. stat says its cold. signal is sent to gas valve to open. gas valve looks to see if pilot is lit via thermocouple. if pilot is lit then main valve opens and burner lights. shortly thereafter sufficient heat builds up to trip heat sensor that turns on fan and blows hot air into house.many times a tripped safty causes a default fan response. aka when you show up the fan is on 24 7 . that equals a failed safety and needs a pro tech to see why saftyfailed.

Oct 18, 2008 | Ruud Heating & Cooling

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