Mitsubishi 1500 fault code fault

Hello members,
I'm an improver refigeration engineer but have been thrown on to an interesting air conditioning problem and I'm hoping someone may have an idea or suggestion to help me solve this fault...

I went to a site which has numerous City Multi Mitsubishi Electric COOLING only A/C units. On the faulty system, in one particular room a ceiling mounted cassette is showing a 1500 fault code which technical have informed me is an overcharge error. This system is piped to another two a/c units in another room (one is a cassette/ the other wall mounted). When one unit is running the unit cools fine, but when all three run the error occurs on either controller.

I have tried to power down all outdoor and indoor units and re-activate, still the fault occured. I noticed a TH1 thermistor was not in it's holder on the discharge line (someone previous must have removed it), I placed it back into position. Also, I found a note on the outdoor unit saying 1kg removed! The system runs on R407c.

Another call has come in because the staff are complaining it's too hot, I hope someone might be able to help me...I'm thinking about removing the gas, and recharging (will try to measure the pipe lengths and make a calculation to charge accurately) but I've been told by staff at the site this has been done before. I hope for any recommendations you guys might have.

Kind Regards,

Neil the PIE MAN :)

P.S It's PUY - P200 YMF - C [OUTDOOR]
PLFY - P8OVAM-A [INDOOR]

check the air temps on all indoor units you should have 12C diff if you find only one giving good cooling it could be the linear expansion valve starving the other fcu s of gas causing liquid flood back to the compressor giving the impression of over charge

Cheers james something to go on will check the air temps when I go back there hopefully I can get it sorted!

City Multi systems constantly monitor
Discharge Super Heat.

High pressure sensor 63hs converted to temperature minus discharge pipe TH1 temperature = DSH.

When the DSH is less than 20 deg C for 15 mins or less than 10 deg C for 10 mins then stop on preliminary 1600 (not displayed on RC)
then
resart operation & if DSH drops into fault conditions again within 60 mins then stop on full 1500 fault.

This is may be whysomeone has taken TH1 out of pipe pocket to make the system think discharge pipe temp is low.

So system is overcharged or problem with discharge pressure sensor or TH1 data.

You can trouble shoot this in about 10 mins easy. Fitting new parts will take a bit longer.

Fit gauge manifold to HP service port.
Put all indoor units in test mode cooling.
Measure true discharge pressure with gauge & compare with circuit board data using SW1 & LED display.
If circuit board thinks discharge pressure is diferent than real pressure then replace 63hs pressure sensor.
Measure discharge pipe temp with your temp meter.
Compare with circuit board TH1 data.
If TH1 data not correct then replace TH1 & fit into pipe sensor pocket.

The DSH should never be less than 10 deg C or the comp is slugging liquid.
Its real easy to check.

BTW
very small chance that its a circuit board problem but £ to a penny its pressure sensor / temp sensor problem.

You might be able to pinch a 63hs & TH1 from another system just to confirm.

Thanks Thermatech I will try it out, can't believe how much there is to know on these A/C units! There's at least 6 other city multi outdoor units which I can pinch parts from and I can test them out as you suggested. Cheers for the reply, Neil.

james10 has good point about indoor unit LEV, so it's worth checking.
If the LEV valve is locked wide open then you have permanant bypass liquid to suction through this unit & lots of refrigerant noise.
So poor or no cooling at the other units as all the refrigerant is flushing through one indoor unit.
Often the refrigerant noise is enough to generate compaint from staff.

But the outdoor unit can cope with some liquid flood back due to the large suction accumulator at the outdoor unit.
BTW
On that model you can check accumulator liquid level with SW1 setting & outdoor unit control circuit board LED display.
If the accumulator is reporting AL=2 liquid level over flow then check operation of all indoor units LEV valves & cooling performance.
If all indoor unit operation ok then go for refrigerant reclaim.
If Accumulator liquid level is AL=1 or AL=0 then double chech TH1 data & 63HS data as possible cause of 1500 fault.

Hello guys,

Just to let you know I went back to the same site today, there was another problem which I had to look at! In the same room x3 other indoor units on another system were not cooling well....
AIR OFF - 18DEGREES
AIR ON - 23 DEGREES
Checked the outdoor...
LP gauge pressure between 4-6bar
Hp 16-23bar!
TH1 thermistor temp 110degrees, what the hell is going on here?!
Found a 1501 error code on the indoor controller on it's history...shortage of gas?

Called mitsi technical they couldn't give me a cause, checked HP on digital which read 50bar, did numerous checks with SW1 on dip switches and the mitsi tech couldn't believe the readings I was giving him from the digital read out...he's advised me to get my company to get a mitsi tech down to site with a lap top to solve the fault. Problem is my company won't pay because it's too expensive, I'm at loss really but a fellow engineer believes I should add 1kg of R407c at a time and see what happens!

Sorry for going on about this but I'm going to recover all the gas out tomorrow, measure the pipe length while on vac and charge, at least I can be sure the charge for that system is correct. Let you know how I get on..my head is mashed!

1501 is caused by oveheat of the compressor.
Compressor has TH10 temp sensor on lower shell.
If Th10 provides correct temperature data it will be due to poor motor winding cooling by suction gas.
So the system is SOG or some problem with refrigerant flow in the system.
In this case some of the indoor unit LEV valve could be failed in shut possition. System works with all indoor unit s cooling but when some have reached set temp & the only ones left requesting cooling has locked shut LEV valves then system runs down to low suction pressure & compressor get too hot & 1501 fault.

I regularly do health check monitor of City Multi systems for contractors with Mnet monitor laptop & provide full report with list of any compenents which need to be replaced or SOG issues.
When this kit was made I was senior technical service engineer at Mitsubishi Electric UK so I know YMF-C systems inside out.

Hi Thermatech,

You was right about the system being possible SOG, only recovered 3.6kg after powering down outdoor and indoor units, the outdoor unit is 7.2kg! Pressure tested system upto 31 bar and shut the suction and liquid ball valves [ran out of time so will return next week to hopefully find the leak]. I think it's only a small leak which will be tricky to find, would you recommened charging with a dye to find the leak? I'm returning next week but thanks for your help, at least I've got something to go on now.

Pie Man

Just to let you know I found a leak when I returned to the site today....thankfully! It was on a dodgey flare on the liquid line, re-flared it and tightened the nut and now no leak yeah, pulled a good vacuum, charged up and now cooling fine. Thanks for all your help.

Pie Man