fujitsu high discharge on heat mode

[savoc]

Hi guys having trouble with a ducted fujitsu r22 aot?. when i got to site the a/c had just been started in heat. i found the hot gas line going to the indoor unit to be very hot (a/c cut out on high discharge temp)and the return liquid line to full frosted it looked like liquid coming back. i assumed the a/c was low on gas. ran the unit on test mode cooling. i then had very high suction pressure for a cold day around 580kpa (not low on gas). i checked the reversing valve, i used a magnet on the valve to check the operation and touch tested the pipes, feels ok. Put the a/c back into heat mode and it ran fine. discharge line was touchable and the return line was warm. house got warm straight away. Air filter was trashed i removed it, carried out compressor capacity test all okay. a/c ran fine for 2 nights now playing up again. i think the electronic tx is ok. I belive it may a reversing valve, what are the correct test for a valve? the customer also said this is the first time its played so no one has ever touched the gas charge. Any glues? dirty indoor coil? faulty valve? check valves?

[chillerman2006]

Hi Savoc

This is not my area, but if you fill in the blanks below + anything else you can add(in both modes), your get your answer alot quicker

discharge pressure
discharge temp
condensor outlet temp
liquid line temp (after drier)

condensor air on
condensor air off

suction pressure
suction temp evap out
suction temp comp in

evap air on
evap air off

how many evaps
any evaps with different figures

I always write my figures down + then seems to fall into place

Hope this helps, R's chillerman

[a/c.king]

Hi savoc
please if you can spacifay the unit model no. or if the unit is 3phase or single phase.
IF IT IS SINGLE FASE IT WILL HAVE X2 CAPACITORS CHECK THEM PLEAS.

[paul_h]

This is a toughy.
High discharge temp on heat (airflow? pipe restriction?)
But high suction pressure on cool (not airflow or pipe restriction)

The liquid line coming back all frost just throws the whole thing up in the air.
There's no indoor flow control, the suction pressure on cooling is high, I mean the whole thing sounds like an indoor restriction.
But it's an old unit (no kinked pipes doubtful), it's intermittant as well, and the unit only has outdoor flow control for the refrigerant.

Probably want to have model so people can look up what is actually in the units.


edit: Where does the liquid line coming back start frosting? From the indoor or the outdoor?

[install monkey]

choked/partially blocked strainer on the suction side before the compressor and after the suction gauge port,hence indicating a high suction pressure in cooling mode,there are 3 strainers on the condenser 2 on either side of the expansion valve and 1 on the suction line.run it and check pipe temperatures on both sides,if over 2 deg change it

[simon@parker]

choked/partially blocked strainer on the suction side before the compressor and after the suction gauge port,hence indicating a high suction pressure in cooling mode,there are 3 strainers on the condenser 2 on either side of the expansion valve and 1 on the suction line.run it and check pipe temperatures on both sides,if over 2 deg change it
if gas charge is same as installed and no one touched it for 2 yrs as he says strainers should be fine if it was 407c would say cut out strainers and do tripple evac on 22 nah be good unless it was poor install which would have shown up by now had very similar problem it was a damper unit went to heat damper shut unit tripped damper opened a little bloody pain to find check yr evap is clear and yr duct has no temp controlled dampers if the end user playing with somat it will be fine while yr there just an idea :)

[install monkey]

and clean the filer and coils too

[simon@parker]

would bet good money that end user messing with unit or duct in some way :)

[install monkey]

is the compressor the right way up and have you heard of vector units that work on 50% of their gas charge,also some members need advice on trying to tame a horse maybe teach it to eat nuts!!!haha

[simon@parker]

well if oil sight glass at top compressor is fine init :) i thought that was a donkey he havin trouble with cos it dint like his green sheen an sticky out ears :) roflmfao :)

[install monkey]

cm's should take her to the fire station,at least one of them would get some,cm can watch for tips haha

[Gary]

I would suspect the indoor check valve is sticking.

On a TXV system, this will be a separate check valve bypassing around the indoor TXV. On a fixed orifice system, this will be built into the indoor fixed orifice device (flowrater).

If this check valve sticks shut in heat mode, the liquid is forced to flow backwards through the metering device, which can cause the liquid line to frost... while backing up liquid into the condenser (indoor coil), causing high pressure.

If this same check valve sticks open in the cooling mode, it can allow liquid to flow around the metering device into the indoor coil, causing high suction and possible flooding.

[savoc]

thanks for your helps guys. returned to site, reclaim refrigerant and weighed was approx 650grams short. weighed in correct charge. also found that 4 zone motors were faulty. My refrigeration experience is in nh3 and large commercial very little in domestic air conditioning. Poor air flow through duct work would cause high head pressure in heating and freezing up in cooling true? Now this may sound like the dumbest question ever but how do you know if there is enough air flow through your duct work before you have problems? If the unit runs 9 outlets and 4 are faulty(closed) this may have been the problem?

[Gary]

... how do you know if there is enough air flow through your duct work before you have problems?

Delta-T (dT) is a good indicator of airflow. Slower moving air has more time to absorb/reject heat as it moves through the coil, so the difference between air on and air off temps (dT) increases. If you know what the normal dT for a coil is, then a substantial increase tells you there is an airflow problem.

[paul_h]

I would suspect the indoor check valve is sticking.

On a TXV system, this will be a separate check valve bypassing around the indoor TXV. On a fixed orifice system, this will be built into the indoor fixed orifice device (flowrater).

If this check valve sticks shut in heat mode, the liquid is forced to flow backwards through the metering device, which can cause the liquid line to frost... while backing up liquid into the condenser (indoor coil), causing high pressure.

If this same check valve sticks open in the cooling mode, it can allow liquid to flow around the metering device into the indoor coil, causing high suction and possible flooding.
This is true and caught me out on a carrier unit before.
But the japanese unit's typically have all flow control in the outdoor unit (capillary, TXV, or ETXV and all check valves), the indoor unit is often just open piping beside the distributor and has no flow control or check valves unless they are multi evap units.
I'm more used to the japanese units, with is why that carrier unit was an expensive lesson to me.
So that's why I don't assume anything anymore and asked for the OP for info on the unit, to find out what is inside it.

[Gary]

This is true and caught me out on a carrier unit before.
But the japanese unit's typically have all flow control in the outdoor unit (capillary, TXV, or ETXV and all check valves), the indoor unit is often just open piping beside the distributor and has no flow control or check valves unless they are multi evap units.
I'm more used to the japanese units, with is why that carrier unit was an expensive lesson to me.
So that's why I don't assume anything anymore and asked for the OP for info on the unit, to find out what is inside it.

I agree. Troubleshooting online is difficult at best. We can't see the system from here and must rely upon the information provided. The more information provided, the clearer our perception of the system and it's problem(s). More info is always a good thing.

[sweimaker]

back to basics, id say.

drag gas out,

charge 350 psi of nitrogen., triple vac,. and start from there. recharge, pull head off txv whislt switched off, if it floods badabinggggggg

[savoc]

i found the problem i think. the liquid line connection to the indoor coil has a little inline strainer. It was fully clog with dirt. cleaned, blew nitro threw pipe work and coil. hope this has fixed the problem.

[install monkey]

Note post #5 correct diagnosis! Fair enough wrong strainer but i highlighted the problem,everyone dissed me"oh its only been in 2years and nobody has mauled with the fridge circuit"-dudla duuuu! (Me blowing my own trumpet)-dont do banjo's or horses-just pigs haha