Frozen suction line

[Slim R410a]

Went to look at a Mitsi Elec MUZ 09 (YV Inveter) which was underperforming.
Cool mode; no temp difference whatsoever with indoor air on on/off.
Outside put gauges on, (410a) head pressure was 10.5bar which seemed pretty low, once comp running full speed, suction at 5-6 bar.
Liquid line was sweating, suction line and accummulator froze over, comp. discharge pipe was not even warm.
Clearly a problem with the charge so going to recover and weigh in correct charge but what I cant understand is if these symptoms mentioned are due to an overcharge or undercharge of refrigerant. From my experience undercharged systems seem to frost on the liquid line?
Am I also right in saying that undercharged system will have a high comp disharge temp as it is starved of refrigerant?
Some help much appreciated.

[rbartlett]

[QUOTE]

Went to look at a Mitsi Elec MUZ 09 (YV Inveter) which was underperforming.
Cool mode; no temp difference whatsoever with indoor air on on/off.
Outside put gauges on, (410a) head pressure was 10.5bar which seemed pretty low, once comp running full speed, suction at 5-6 bar.

shortage of refrigerant seems the first option to check..

Liquid line was sweating, suction line and accummulator froze over, comp. discharge pipe was not even warm.
Clearly a problem with the charge so going to recover and weigh in correct charge but what I cant understand is if these symptoms mentioned are due to an overcharge or undercharge of refrigerant. From my experience undercharged systems seem to frost on the liquid line?

there is no hard and fast rule as the shortage can be from 1-100% which means various symptoms as the % changes

Am I also right in saying that undercharged system will have a high comp disharge temp as it is starved of refrigerant?
Some help much appreciated.

see above. however the smaller % loss the higher the likelyhood of a H.D T occuring..

Cheers

Richard

[A Deeb]

your unit seems to be over charge, or evaporator fan not running. mostly these to reasons makes the suction line frozen. and take a look to the return air filter. it may be too dirty need to be replaced.

[1torr]

Reversing valve could be stuck part way.Try measuring temp on inlet/outlets.

[rbartlett]

Reversing valve could be stuck part way.Try measuring temp on inlet/outlets.

so how does this cause icing up..?

cheers

richard

[Slim R410a]

Thanks for the replies.
Filters are as new and I very doubt it is a 4-way valve problem.
Also ran the system on heat mode along with the same split which serves another room next to it. The difference in heating performance was noticible between them, one having an air off of 45degc and the one I am working on 30degc. (22degc air on)

[nicolacozma]

Hi mate,

I'm new on the forum and this is my first reply.
This behavior can be produced by a closed one circuit of your evaporator. Check if all the bending curves are wet on the left side of the evaporator.(on cooling mode).

Also you can set it on the heating mode and if you have a closed circuit of the evaporator you will have an anormally HP(much higher than normal)

I don,t think that is a problem with a 4-way valves because in that case you will have a HP lower than normal and a BP higher than normal.

Best regards,

Nicola

[NoNickName]

It looks like an excessive subcooling caused by too much refrigerant. Please check the liquid line temp. leaving the condenser.

[rbartlett]

It looks like an excessive subcooling caused by too much refrigerant. Please check the liquid line temp. leaving the condenser.

there is no liq line leaving the condenser...


cheers

richard

[NoNickName]

there is no liq line leaving the condenser...


cheers

richard

No? Is it magic?

[rbartlett]

No? Is it magic?

the expansion device is in the condenser..

cheers

richard

[NoNickName]

Well, the condenser condenses and the evaporator evaporates, whatever the cycle is.

[Lowrider]

Right!

If it is a heatpump there will be an expansionvalve situated in the outdoor unit along with a fourwayvalve.

Most of these units will come prefilled up to 10m of single piping length. if the unit's are closer to each other the charge will be too high!

If it's futher away, more charge will be required and if i remembered correctly the units shouldn't be futher apart than 20 m

Give us the suction pipe temperature, suction pressure,
liquid pressure and temperature, head temperature and if possible discharge pressure

[Peter_1]

the expansion device is in the condenser..
richard

Every condenser has a liquid outlet, what you meant I suppose was an expansion device in the outdoor unit but not in the condenser.
And if the expansion device should be soldered direct in the last tube, event then there's a liquid line, perhaps only an inch long but there's one.

[wolf]

hhahahha richard you right 100% gas leak!!!

[taz24]

No? Is it magic?

No not magic.
But on an air cond the liquid supply line is actualy full of saturated liquid that is being transfered to the evap so the heat transfer process can begin. That is why the smaller of the two lines is insulated, it prevents the heat transfer begining too early and therfore no liquid being left for the evap.
The expansion device is on the outlet of the cond unit.

Cheers taz.

[NoNickName]

Thanks taz. I'm an RE since ages, I know how HPs work. My comment was ironic.

[taz24]

Thanks taz. I'm an RE since ages, I know how HPs work. My comment was ironic.

opps I missed it sorry

Cheers taz.

[Electrocoolman]

Hi, If the unit is a Multi-split heat pump unit, then there will be one reversing valve but each circuit will have its own expansion device....on modern higher spec units these tend now to be electronic expansion valves rather than fixed orifice devices..

Surely...the symptons suggest that one valve could be faulty (stuck open) causing a low pressure drop across EEV, therefore suction side (pressure & temp) will not be low enough, and there will be an excess of refrigerant on this circuit causing the frosting back. There will be less heat load on the system which will also lower the discharge pressure.

The other unit on the system might still work to a degree but could be partially starved when they both try to run together.

Needless to say with only one reversing valve both indoor units have to be selected to the same 'mode'.

Adrian

[rbartlett]

hhahahha richard you right 100% gas leak!!!

thanks ;-)

cheers

richard

[Slim R410a]

Just found this thread, didnt realise I did not update.

Recovered charge, was found to be exact (holding charge plus what we added for 15m run) so no shortage of gas.
On futher inspection of the indoor unit, found part of the plastic fan blade to be smashed, so around 30% of the blades were missing i.e. some idiot had been poking things in the wall mount, breaking the blades

Fitted new fan rotor, system pressures back to normal and suction line had a nice sweat.

However, got called back a few weeks later to 'room not cooling down and units leaking'.
Went into room, room temp about 25degC, with the wall mount running flat out with a setpoint of 16degC. Louvre blades on wallmount had excessive sweating causing water to drip.
These were installed in 2004 by myself, back then I was apprentice so didnt know much about sizing etc but turns out that we fitted them as subbies for a building company and thier 'architect' had claculated the load for the room at 2.5kW. (nominal) Room size approx. 6m x 4m, 18-20 people, (councelling room) three large south facing windows! Working this out now I'm getting at least 7kW!
Spoke to Mitsi they said the sweating louvres were a sign of undersized system.