city multi not heating

[Niall.199]

Hi everybody im looking for some help with a city multi pury-p250 ygm-a we have just taken over a new contract the air con was installed 2 years ago and has never worked 100% . The system will not heat when we arrived on site the fist thing we noticed was that there was a vibration in the liquid line going to the bc and also found that the system had 10kg to much gas in it so we recovered all the gas and measured pip runs vacumed and put correct amount to gas in it when we run it we found that the system would still not heat. The unit is running at 28 bar high side and 6.8 low side the compressor is running at a constant 22 hz it does not apper to be speeding up im still not sure why i am getting vibration on liquid line possable blockage maybe has anybody any suggestions what to try next

[multisync]

Get Thermotech to fly over. He will bring all his test kit and 30+ years knowledge to bear. He will get that system running perfect or know what's needed to make that happen. Job done in <2 days. Then you carry on with a happy customer who thinks you are the bee's knees.

Or you can keep coming back here and asking questions spending days and days at site trying things as the customer gets more and more despondent.

Or you may get lucky..

You pay's your money (or rather the customer does)

[Thermatech]

The compressor has arrived at target discharge pressure & can then maintain target by only running at minimum compressor speed.
This is most likely due to some blockage or restriction in the system at some unkown location.
Somebody has mistaken poor performance for shortage of refrigerant & has ended up overcharging.
But if refrigerant is not returning back to the outdoor unit from the system then adding refrigerant is not going to make any difference.

The prime suspect will always be LEV3 at the BC box. When all indoor units are in heat mode this electronic expansion valve is the only way liquid refrigerant can flash off into the suction line & get back to the outdoor unit.
The other thing to check is that the pressure sensor data for the pressure sensors at the BC box & outdoor units are correct by SW1 setting & service maniford gauge readings.
Also make sure 4WRV has changed over to heat mode correctly. Try putting 2 sets of gauges on the outdoor unit , one set on the service valves & one set on the HP LP service ports. This can help to see if any high to low bypass at outdoor unit.

Remember in heat only mode the outdoor unit pumps hot gas only to the BC & suction pipe is in effect an extension of the outdoor coil as the liquid returning from the indoor units is flashed off into the suction line at the BC through LEV3.

[Thermatech]

Thanks for your recomendation Multisync.

It that time of year

Most City Multi trouble shooting site visits are due to poor heating performance as we start getting some proper cold weather.

[Niall.199]

i have done a number of checks on the outdoor unit dip switches lev3 is 150 does that sound right to you

[Thermatech]

No
If all indoor units requesting max heating then LEV3 should be more like 400 to 600.
So that why you have poor heating performace at indoor units & compressor only running at slowest speed.
There is some problem which is causing the BC box to think that it needs to shut down LEV3 to small opening.

I had one like this 2 weeks ago & found one of the BC Box pressure sensors providing pressure data 8 bar too low. So BC box was trying to maintain its target pressure differential for heat mode & control logic was closing down LEV3 to small opening.

Suggest check P1 & P3 with SW1 after 10 mins system stop for equalized pressure data which should match outdoor pressure data on HP & LP sensors & manifold gauge readings.

When operating at heating mode the box will target 3 bar diff between P1 & P3 with LEV1 closed at 60 or only slightly open ,, say 120 to trim pressure to maintain 3 bar diff.

BTW
If the system has been like this since installation then double check all pressure sensor , LEV & temperature sensor connections at the BC circuit
board. If the LEV plugs are not fully connected or in the wrong way around then this could cause this type of problem.

[Niall.199]

cheers for the info i did check p1(30.3) and p(26.3) how does that sound to you

[multisync]

Thanks for your recomendation Multisync.

It that time of year

Most City Multi trouble shooting site visits are due to poor heating performance as we start getting some proper cold weather.


Been even better if I'd spelt your name right :-)

[Thermatech]

System Heating target is around the 30 bar mark so P1 is bob on for target.
BC target P1 tp P3 at 3 bar diff so 26 bar at P3 is close enough as it will always tend to drift up & down a bit.

But is this the real pressure or are the pressure sensors reading wrong pressure.

Something is making the LEV3 ramp down to small opening so suggest do the standing pressure test to make sure all 4 pressure sensors are reading the same pressure after equalisation & check against manifold gauge readings.

I cant do much more without putting the laptop on the system to monitor what is happening.

[multisync]

I cant do much more without putting the laptop on the system to monitor what is happening.

You give away too much as it is.. We are all for sharing info but some need to make a living from this level of service, giving it away could be considered far too cheap..

[Niall.199]

Thanks for your help ill check sensors tomorrow

[Niall.199]

Thanks for your help I had a faulty p3 sensor changed it the system is working perfect now