Lennox unit problem

[marc5180]

Hi guys, we took over a contract of a restaurant last year and we inherited a lennox ducted ac unit. We've had nothing but problems with it from day 1.
The condensor is a KVHK48.DVFC.

The condensor is situated outside in the carpark. The evap (indoor unit) is also outside in the car park. The indoor unit is a ducted unit which ducts straight into the restaurant a few floors up.

From day 1 we have had many many problems, from 4 way valves failing (2 circuits) to defrost problems, to thermisters, to control faults.
We also had a case where the discharge air from the condensor blows out above the back of the coil, which then gets sucked back on to the conensor coil thus giving high head pressure.
We had something made to direct the air away from the condensor coil and this seemed to solve the problem and the system worked fine.... for a few weeks.

The we got a call saying the unit had wasn't heating. We arrived back on site and because the outside temp had dropped to -3DegC the supply air was only 18Deg C. I spoke to Lennox who said that oncoil evap temp should be a minimum of 13 DegC. The return air that comes back from the restaurant comes down a 300m x300m duct work which goes onto the back of the coil but the fresh air is 2.5m x 1m..

Lennox said to block part of the fresh air inlet and see if the temp rose, which it did. We left it at about 80% blocked off, and the temperature rose, the air off went up to 30DegC.

This was fine for a few months until we got a call back saying that it wasn't working again. I got to site and found compressor 1 down to earth. A building was being refurbished at the back of the restaurant and the brick dust had covered the condensor and evap coils thick. We hosed the coils down then ordered a new compressor. Another guy went back and fitted it and ran it up but found a relay needed changing. So he swapped the relays around to try and recommission the new compressor circuit but... he said he ran it up and all was well for 20 mins or so. Pressures and temps were fine. Then the compressor started making a loud noise and the discharge dropped to 5 bar and the suction became warm to touch.

I told him to turn it off as there could be liquid getting back to the compressor due to not enough air flow across the evap, what do you guys think?

I plan on going back tomorrow to be sure that theres no liquid getting back to the compressor. I also want to check if there is enough airflow across the evap but im not sure how to check this, can any of you guys help?

[Gary]

Sounds like you need to be very thorough in both inspection and repair, looking for design and installation problems as well as problems that have developed along the way.

IOW, you need to start from scratch.

[Brian_UK]

Don't you just love Lennox units

Sorry to read your story Marc but it is so familiar to most of the old units that I have had to work on.

USA spec doesn't seem to work in the UK.

[Daikin=Overated]

Ditto the above Brian!

I've a site with a Lennox package that's suffered the same ill fate to the example given in the original thread above. In fact theres a couple of things learned from this thread that I'll try next time round as shock horror my system I mentioned is still down.

Marc. If I read this correctly are you saying theres some distance between the CCU and the evap, or otherwise? If so could it be that your low on oil and running it up allowed for an oil loss in the compressor after 20mins or so of pumping round the system?

Also, check your guy hasn't inadvertently reversed phasing (if 3ph). Especially if it's a Copeland. That said, if your guy was stood there with his gauges hooked up then he should have seen it trying to pump down straight away. Sometimes comp manufacturers make a slight amendment to their models and the connections that can easily be overlooked when presuming your doing a like for like when providing all the correct model numbers etc for the pot.

Let us know what you find.

P.s Also to add having re-read the post, if your experiencing cold outdoor temps at those tempretures stated the comp should have a heater jacket, strap or whatever you know them as otherwise yes, it's possible you'll get liquid migrate to the coldest part of the system!!

Regards,

J.

[marc5180]

The evap and condensor are pretty close to each other, i'd say less than 5m and the rise to the evap is no more than 2m, so all in all a pretty short pipe run.

The compressor (copland scroll) was put in and he's sure that he didn't get the phases mixed up, he just did a like for like but this is something i will check tomorrow.
The crankcase heater was on the new compressor for around 3 hours before the new compressor was even switched on, so there shouldn't be liquid in the compressor.

Both compressors have plenty of oil in the sightglass on the compressor so again i dont think it's lack of oil.

My thinking was that because there isn't ( or if there isn't) enough airflow across the evap, latent heat change cannot happen.. so the liquid in the evap will not change to a vapour before it goes back to the compressor... Maybe i'm wrong though

[Daikin=Overated]

The evap and condensor are pretty close to each other, i'd say less than 5m and the rise to the evap is no more than 2m, so all in all a pretty short pipe run.

The compressor (copland scroll) was put in and he's sure that he didn't get the phases mixed up, he just did a like for like but this is something i will check tomorrow.
The crankcase heater was on the new compressor for around 3 hours before the new compressor was even switched on, so there shouldn't be liquid in the compressor.

Both compressors have plenty of oil in the sightglass on the compressor so again i dont think it's lack of oil.

My thinking was that because there isn't ( or if there isn't) enough airflow across the evap, latent heat change cannot happen.. so the liquid in the evap will not change to a vapour before it goes back to the compressor... Maybe i'm wrong though

Yeah but you said you cleaned both coils as found to be blocked right? Unless theres an evaporator filter blocked the only other devices causing the coil to flood is the metering device, or a faulty evaporator fan motor.

I have also had to change a condensor fan motor on a Lennox as the bearings caused intermittant seizure. I think theres a fan speed controller on these models worth checking too.

I would urge you to check this once you've verified your phases on the new Copeland to ensure the TXV's not failed open. Copeland compressor renewal has caused me and others loads of bother in the past, hence my suspicions on this note.

[Gary]

Figuring out what's wrong before getting to the jobsite generally results in making all the wrong moves. Keep an open mind and see what you've got when you get there.

[marc5180]

Yeah but you said you cleaned both coils as found to be blocked right? Unless theres an evaporator filter blocked the only other devices causing the coil to flood is the metering device, or a faulty evaporator fan motor.

I have also had to change a condensor fan motor on a Lennox as the bearings caused intermittant seizure. I think theres a fan speed controller on these models worth checking too.

I would urge you to check this once you've verified your phases on the new Copeland to ensure the TXV's not failed open. Copeland compressor renewal has caused me and others loads of bother in the past, hence my suspicions on this note.

Yes the coils were filthy but we have blocked off the fresh air supply around 80%, limiting the air onto the coil.

I have checked the evap fan amps against the dataplate and they checked out ok. Not sure about a fan speed controller but i can look at that tomorrow.

Whats the best way to test TXV's? Just hold the sensing bulb? what should i be looking for?

I've never really had many problems with TXV's failing so im a novice at fault finding with them.

[marc5180]

Figuring out what's wrong before getting to the jobsite generally results in making all the wrong moves. Keep an open mind and see what you've got when you get there.

I do agree Gary but this discussion will give me a few things to think about once on the job that i may miss otherwise.

[wambat]

Was the fan inspected closely because I would be suspicous of the supply fan being loaded with a layer of grease and brick dust this being a restaurent.

[cmac]

Another guy went back and fitted it and ran it up but found a relay needed changing. So he swapped the relays around to try and recommission the new compressor circuit but... he said he ran it up and all was well for 20 mins or so. Pressures and temps were fine. Then the compressor started making a loud noise and the discharge dropped to 5 bar and the suction became warm to touch.

I told him to turn it off as there could be liquid getting back to the compressor due to not enough air flow across the evap, what do you guys think?

Hey there, maybe I'm over simplifying but, if the suction is warm, maybe the 4 way valve is at fault. If liquid was getting back to the compressor, would the suction not be be cold.

[Gary]

Pressures and temps were fine. Then the compressor started making a loud noise and the discharge dropped to 5 bar and the suction became warm to touch.

Could be an internal pressure relief. Possible overcharge or insufficient condenser airflow.

[marc5180]

Was the fan inspected closely because I would be suspicous of the supply fan being loaded with a layer of grease and brick dust this being a restaurent.

Both fans were cleaned throughly with a jetwash and coil cleaner.

[marc5180]

Hey there, maybe I'm over simplifying but, if the suction is warm, maybe the 4 way valve is at fault. If liquid was getting back to the compressor, would the suction not be be cold.

Both 4 way valves have been changed in the past as they were both stuck.

[marc5180]

Could be an internal pressure relief. Possible overcharge or insufficient condenser airflow.

The standing charge was weighed back into it when the compressor was installed. The condensor coils have been cleaned throughly and the condensor fan is working to spec.

[Gary]

The standing charge was weighed back into it when the compressor was installed. The condensor coils have been cleaned throughly and the condensor fan is working to spec.

Possibly an intermittant fan problem then.

Does the unit have a HP shutoff?

[marc5180]

It does have a hp shutoff, wired in series with the lp switch and the motor protector. All of which check out ok.
I'm going back this morning so i'll let you know my findings.

[Daikin=Overated]

Both fans were cleaned throughly with a jetwash and coil cleaner.

It's the fan motors internal bearings that will give you the problems not any external parts like the blade or drum (which is enclosed in housing from memory). Point being there very difficult to fault find when intermittant, when there running they'll give you the correct amperage readings, it's when the bearings get hot from runnning that they struggle to start again.

In my case this was on the condenser side of the package system so the HP would hold things out, allowing me to trace the fault that way.

I was thinking too, theres no phase reversal protection on these systems so the compressor would run regardless, the only saviour being that the engineer spotted this and shut the system down.

N.B Don't be decieved if you find the phases are indeed like for like on the pot connections. It's the changes made on the wiring internally by Copeland that require two of the phases to be reversed to run the comp the right way round (once you've verified this is the fault of course). It's the suction you need to observe and if possible update your findings here as theres no mention of what your engineer said the low side was doing............in my mind pumping down!

Best of luck for today. Let us all know of your findings!

J.

[marc5180]

Got back to site today with the aim of getting both circuits up and running one by one. I fitted both new relays then started with circuit 2 (the old compressor).

As the restaurant was cold, (return air 15DecC) i put the setpoint on the York controller to 30DegC. This brought on circuit 2 compressor but it ran for a minute or so and knocked off. I checked the Lp, Hp, motor protector and it hadn't knocked off on any of these. I reset it and watched the compressor amps get up to around 14a per phase and the compressor temp got up to 55DegC. None of these seemed to be the problem. Next i disconneceted the compressor and ran the circuit up. The condensor and evap fans both started and i left them running for 30 mins whilst watching the amps. It didn't knock off once.

I connected the compressor back up but it kept knocking off. I disconnected the controlls signal from the external york controller in case it was a controll issue and linked across G-R R-Y1 Y1-Y2 (G being indoor fan, R 24v input, Y1 and Y2 compressor 1 + 2)
This brought both compressors on and they ran fine for an hour, didn't knock off once.
The supply air rose to 39 Deg C air off, which is the highest i have ever seen it and the return rose to 24DegC which again is the highest i have ever seen it.

I took down the readings that i got which were liquid line pressure 18.7 bar 45degC SCT which gave me a subcooling of 19K. Suction pressure was 3.4 bar, SST was -1DegC and a superheat of 2.8K.

I then linked across the 4 way valve to put the system on cooling. Circuit 1 ( the one that the other engineer said he had problems with) came on and beguan cooling, pressure and temps were fine and subcooling was 14K whilst the superheat was 9K. However.......

Circuit 2 kept tripping out which i traced to be an LP fault. Again i connected my gauges and noticed the suction pressure dropping rapidly until it got down to 0.6 bar then it would cut out on LP. I measured the subcooling at the liquid line and found 15K, which led me to think faulty expansion valve I took off the bulb and warmed it in my hand but nothing happend, no change in pressure and the compressor kept tripping on LP. I think the expansion valve has failed, the bulb was mounted tight and was insulated well.

Before i left i connected the York controller signal wires and watched as the unit kept tripping, so i do think its a controlls issue but on the cooling cycle circuit 2 has a faulty expansion valve. Thats my thinking anyway

[Brian_UK]

Well done Marc, sounds like a productive day.

Even if it isn't fully resolved yet it is getting there.

[Gary]

19K subcooling is excessive.
15K subcooling is excessive.
14K subcooling is excessive.

Subcooling should be no more than 8.5K

Looks like overcharge to me.

[Gary]

Circuit 2 kept tripping out which i traced to be an LP fault. Again i connected my gauges and noticed the suction pressure dropping rapidly until it got down to 0.6 bar then it would cut out on LP. I measured the subcooling at the liquid line and found 15K, which led me to think faulty expansion valve I took off the bulb and warmed it in my hand but nothing happend, no change in pressure and the compressor kept tripping on LP. I think the expansion valve has failed...

Or perhaps its inlet screen is plugged.

[marc5180]

Well done Marc, sounds like a productive day.

Even if it isn't fully resolved yet it is getting there.

Thanks Brian but it wont be long till something else goes wrong with it

[marc5180]

19K subcooling is excessive.
15K subcooling is excessive.
14K subcooling is excessive.

Subcooling should be no more than 8.5K

Looks like overcharge to me.

I agree it does look like overcharged but i changed the 4 way valve on this circuit and i personally weighed the correct charge back in.

The TXV cant be taken apart though can it, to look at the inlet screen? If it needs taking out of the sytem to be opened up, is it not better to change it?

[Gary]

None of this accounts for the discharge gas dumping into the suction line. Overcharge could do it, the discharge pressure building up and tripping the internal relief.

[marc5180]

I spoke to him yestrday and he said it wasn't the suction that was getting hot it was more that the discharge was getting cold. The compressor began to ice up and the discharge went down to 5 bar and became really cold.

[Gary]

I spoke to him yestrday and he said it wasn't the suction that was getting hot it was more that the discharge was getting cold. The compressor began to ice up and the discharge went down to 5 bar and became really cold.

It started doing this while running? Or did this happen on start-up?

Is there a fan speed control on the outdoor coil?

Does the unit have an accumulator?

I still suspect an overcharge. That's a lot of extra subcooling, indicating that liquid is backing up into the condenser.

[marc5180]

This happened after it had ran for a while. He said the compressor began to get really cold and the coil began to freeze up so all i can think is that the system may have gone on defost and something went wrong.
It uses dampers to controll the head pressure and they do have an accumulator.

[Gary]

I am picturing a condenser with excess liquid backing up due to overcharge suddenly becoming an evaporator (defrost cycle) and sending all of that liquid back to the compressor, apparently enough to overwhelm the accumulator.

[Gary]

Be sure to lubricate those dampers. They can really screw with the system if they stick.

[marc5180]

I know the charge is correct though otherwise i would have to agree. I'm going to reclaim the refrigerant on Monday though to be absolutely positive. I think i will lubricate the dampers and check the actuator on monday.

[Gary]

This must be a very old system. i haven't seen condenser dampers in a very long time.

[marc5180]

You would think so but its less than 5 years old. I have never seen head pressure controlled by dampers so its a new one for me.

[Gary]

As I recall, they were a maintenance nightmare back in the old days. Let's hope this is the new improved version, with better materials and such.

[marc5180]

Lennox say it's a very efficient way to control the head pressure. Wether its true or not i don't know.

[Brian_UK]

Lennox say it's a very efficient way to control the head pressure. Wether its true or not i don't know.

It can be until corrosion sets in around the swivel pins or the actuator springs a leak.