Mitsubishi Heavy Ind A/C Split Problem

[pie man]

Just wondering if anyone could help me on air conditioning unit.

The fault....

Mitsubishi Heavy Ind wall mounted split on R407C, which faulted out on the timer/check light flashing five times - this I believe means SOG.

The history on the unit is that there has been different parts replaced i.e compressor, fan motor, outdoor PCB, capacitor etc, this is what the customer has told me costing around £2000!

Therefore I recovered the gas which was 3.2kg, after measuring the pipe run and outdoor charge it should have been 1.78kg so obvious over charge. I pressure tested up to 360psi, no leaks occured and then vacced out. Charged correct amount and ran unit. It cuts in and out of temp fine, air off got down to 4 degrees. However suction was around 45psi/ hp 260psi which I recognize to be slighty short should be around 55-60psi?

I didn't want to add anymore gas incase I was making the same mistake the previous engineer made but I'm concerned this could alarm out again over time. Anyone got any ideas why this could be occuring? Your help/ opinions are welcome.

Thanks, PIEMAN

[install monkey]

choked drier?

[The Viking]

Sorry Pie Man,
Pressures on their own doesn't really tell us that much.
What wast the sub cooling and super heat?
What was the indoor and outdoor temps?
Did it run in heating or cooling mode?

Coming to think of it, what model is it?
Did you recharge with fresh, virgin. R407c? (Sometimes imbalances in the R407c due to leaks or engineers charging as vapour will cause all sorts of problems)

Soo many questions, sorry

[pie man]

Hello Guys thanks for the quick response.

Install Monkey I don't think its a choked drier because added nitro through the high side and it went around through to the suction ok. I don't think they changed the original drier when replacing compressor so possibly a slight blockage?

Viking details are

MODEL INDOOR FDKN308H [ambient 20 degrees]
OUTDOOR FDCP308CEN3 [ambient approx 6 degrees]

Also, spoke to HRP who deal with MHI & said to check the air off/ coil sensors both tested out ok at 6 k.ohms.

However I didn't take subcooling [is that reading air temp behind cond coil using a comparator?/ or superheat ; compressor suction pressure convert to temp - temp at evap inlet?].

If it bounces back in will defo take them readings should of have done while I was there.

I understand its pretty difficult to diagonise if you aint there on the job but any advice or ideas would be greatly appricated. Thanks in advance,

Pie Man

[pie man]

OOPS, other question Viking about R407C, it was half full the bottle I used but defo charged as a liquid being 400 series!

[install monkey]

test to see if theres any td accross the driers,strainers- did u vac both sides of the system and to prove all the nitro was out the system

[charlie patt]

ive had issues with early mhi on 407c waxing the eevs when they get near setpoint the eev shuts down and steeps in and out but the wax holds it in and pulls suction down lower than should be mainly when hot the wax gets tacky so when you go there it run fine 6 hrs later it faults personally 407 is a horrible blend it waxes like hell on these units

[pie man]

Thanks again for the responses guys,

Install Monkey I had two access points suction pipe with the shut off valve and a brazed schraeder line for discharge, vacced both sides for a couple hours only a 11m pipe run from outdoor to indoor. I would have liked longer but wasn't really given the time to vac over night and yes I'm desperate for a torr gauge. I know not good going off manifold gauges. I've got a strong feeling it will come back in again so will check the td for the drier.

Charlie sounds like there aint a solution for these particular units lol! If keeps faulting they may just rip the bloody thing out. Come to think of it there's a maintenance coming up in a couple months so I shall definitely be returning soon to site...will see what happens and let you know if it faults again!

Thanks for the comments much appricated, I love this site!

[jason09]

4 deg pretty low wot ur air flow like, filters and coils clean?

[moondawn]

4 deg pretty low wot ur air flow like, filters and coils clean?

I been servicing units and when on cooling i sometimes get air offs at 4 deg c. If they are put on to test run would this be different from putting them on to normal cooling ie 18 deg c on the controller with load in the room? i always thought it would be the same just forces sensors to be bypassed to bring on the unit?

[r.bartlett]

Just wondering if anyone could help me on air conditioning unit.

The fault....

Mitsubishi Heavy Ind wall mounted split on R407C, which faulted out on the timer/check light flashing five times - this I believe means SOG.

The history on the unit is that there has been different parts replaced i.e compressor, fan motor, outdoor PCB, capacitor etc, this is what the customer has told me costing around £2000!

Therefore I recovered the gas which was 3.2kg, after measuring the pipe run and outdoor charge it should have been 1.78kg so obvious over charge. I pressure tested up to 360psi, no leaks occured and then vacced out. Charged correct amount and ran unit. It cuts in and out of temp fine, air off got down to 4 degrees. However suction was around 45psi/ hp 260psi which I recognize to be slighty short should be around 55-60psi?

I didn't want to add anymore gas incase I was making the same mistake the previous engineer made but I'm concerned this could alarm out again over time. Anyone got any ideas why this could be occuring? Your help/ opinions are welcome.

Thanks, PIEMAN

Sounds like it's running normally. Why would you expect 60 psi on a split in 6 deg c outdoor temp?

Has it tripped since you did the above?

[pie man]

Hi Jason the coil and airflow are fine however the filters are missing I have told them they need replacing!

Moondawn I didn't operate on test run but would be interesting to try that and compare airflow temps.

R bartlett it's a fair point about the low ambient temp outside I did mention that to the Mitsi tech, just its bounced in a few times according to the customer, not bounced in since I recharged but only been a week so fingers crossed it wont come back in again!