evaporator flow problem

[Gorref]

I have been all over this system with no definate answer. Walk in freezer, old 502 sytem changed to HP80 when a new condensing unit went in. Two evaps, room suddenly will not go below 20 F. Liquid and suction driers replaced, solid column of liquid at both tev. New tev's installed, not able to flood the evaporator no matter what I do, except turn off the fans and wait. Running 35 lbs suction, 250 lbs head, 32 F superheat, 25 f subcooling. it just will not flood the evaps. I am thinking a blockage in the evap. Old oil logged? Did not do the refrigerant change. Any thoughts?

[Grizzly]

Suction Driers?
Why?
It certainly seems that there is a blockage
What were your old liquid line driers like?
You may have a point about the oil particularly as the 502 system oil will have been mineral.
I have not retrofitted any R402a systems yet so over to those who have?
Grizzly

[coolhibby1875]

if there was a choke/blockage it still would not freeze around the coil with the fans off!

[monkey spanners]

Has it got a liquid/suction heat exchanger? they have been known to colapse internally and restrict the flow.

What oil is in your new unit? I think hp80 is a drop in for R502 so should be ok with mineral oil or ester.

Another one that i have seen it defrost heaters stuck on.

[cadwaladr]

i [presume you vacced out this system,and charged it in the liquid phase are you sure of the quality of the hp80,whats the temp of the ambient/the liquid line

[Grizzly]

if there was a choke/blockage it still would not freeze around the coil with the fans off!


Surely it depends where the blockage is?
Just a thought!
Grizzly

[coolhibby1875]

Surely it depends where the blockage is?
Just a thought!
Grizzly

wouldn't have thought so?

[Peter_1]

...
What oil is in your new unit? I think hp80 is a drop in for ....
Totally agree, this can't be the problem

[Gorref]

Thanks for all the feedback, this is a flow restriction problem for sure. I have really been over all the basics. my take is it like there is a EPR on this coil.I also have seen pipes colapse in evaporators but there are no signs of that. i am thinking oil sludge or internal pipe colapse. I am normally the one to answer the questions for the young guy's but this one has me working overtime......the other guy's are loving it.

[Peter_1]

Or the distributor is clogged. Measure once temperature of every bend of each circuit in the coil to make sure no circuits are restricted.
The circuits normally follow an identical flow circuit

[Gorref]

even flow through all circuits, frosts through first pass and then seems to loose liquid. even warming the bulb on the TEV doesn't incease flow. I am now thinking suction restriction. Getting sick of this place.

[Grizzly]

I repeat my original question!
Why are suction filters fitted?
Grizzly

[Gorref]

Sorry standard on keeprite condensing unit, replaceable core type i just installed a new suction filter, ran it without one no difference. I am going to measure temperature along the suction line to see if I can find a temperature drop.

[Peter_1]

even flow through all circuits, frosts through first pass and then seems to loose liquid. even warming the bulb on the TEV doesn't incease flow. I am now thinking suction restriction. Getting sick of this place.

Faulty new TEV or orifice too small.
Do you have problems with or 2 rooms?

[mikeref]

Hi Gorref,I had something similar to this at a supermarket freezer, the valves were recieving liquid however due to refrigerant change and liquid line size and run length, there was a pressure drop from reciever to expansion when under load, hence poor cooling. Try fitting a sight glass before tx to test this. cheers, Mike

[Gary]

Faulty new TEV or orifice too small.
Do you have problems with or 2 rooms?

I agree. Sounds like undersized orifices to me.

[Deniver45]

Gary,
I hope you read this;
I have the same problem on a low temp 404A walk in freezer; it won’t drop UNDER 20 degrees. This condensing unit is under the buildings roof and above a drop ceiling on the box top in a space that is 120 degree's; ALSO THE CONDENSER FAN IS 6 INCHES FROM THE BACK WALL!

I am not exsagerating here............... the fan inlet is 6 inches from the back wall.

When you open the main door to the case, the evap is on the left side of the box and NOT to the rear of the freezer. The ambient outside the freezer is 90 degrees and the space surrounds the condenser has to be in excess of 115 degrees.

However the owner @ this Chinese rest. Swears it was @ 0 degrees in the summer, last year here. I don’t believe her; not with this poorly designed box.

I have never a walk in freezer designed so poorly. The condensing unit should be at least an equal length of it's length away from the wall and the condensing unit should be on the roof of the building; only 6 more feet higher.

The TX; it is external EQ. and one of the circuits was starved; I have a sight glass on the liquid line past the receiver which is a Parker 5" diameter X 10" high = 6Lbs X .09 for R 404A = a good place to start after recovering.

2 AC companies were there before me and could not work a king valve and dumped a whole 30lb virgin tank of 404A in to the room when they removed their gauges. They were all over that TX and even hacked up the stem with pliers.

So at the TX , I finally opened the starved circuit and then I THINK the tonnage is wrong on this TX. The box is 6' X 5' 2" and SURE I checked for leaks at the seals, I checked for excessive frost and ice = none.

So after recharging; I then shortened the defrost time to from 15 minutes to 10 minutes because all 3 heaters were working fine and I cycled it and 10 minutes melted everything down = the same problem…………………20 degree’s.

I then increased the defrost time to 30 and then 40 minutes so the termination switch would end the defrost cycle to make sure the clock was not = same problem, wont drop under 20! The door gasket is fine.

Also they changed the Sporland dryer for the old type Emerson "BB filter" which is fine.......... I prefer the solid sporland core though.

I have a low suction at the evap ( -40 degrees ), but an unusually high superheat / suction at the compressor after I adjusted the TX to feed the starved circuit. So again I removed 10oz of refrigerant to make sure there was no liquid at the compressor suction.

The superheat at the compressor is at 20 which is Copeland’s max.......... but it was 12 before I moved the TX stem = SOMETHING I NEVER DO = never had too! and now again one of the circuits is starved…………. But the other 2 are cold as they can be and look great. I figure I am operating @ 2/3 capacity here and just wanted to get some idea’s from you guys.

The superheat at the evap shows high because I can't get a temp clamp on this evap right = no room, so I tried my Fieldpiece K-TYPE thermocouple wire which is the yellow sensor with the velcro ZIP;
I have never a walk in freezer designed so poorly.

I am worried that IF I change the TX; I might have the same problem because of the excessive heat in the space where the condensing unit is and because the condensing unit is so close to the wall.
What would you do next here?

Thanks......................

[mikeref]

Hi Deniver, 3 circuits and 3 tx valves off one condensing unit? I'd start by checking all orafices are the same then close down valves and open all 3 equal amounts in increments, who knows what could have been done to this overheated unit in the past! Maybe some portable fans for the temperature?

[Deniver45]

Hey Mike,
Did I write 3 TXV's in my letter? I can't see it there! NO, there is only one TXV and 3 circuits off the one manifold. The TXV feed's the manifold that feeds the 3 circuits that go back and forth through the evap. I have always called them circuits. Some call them different I guess. I used to sell a LOT of RC to you guys in Queensland. These guys LOVE the MDS RC airplane engines over there mate.

[tonyelian]

hi
it seems like a small condensing unit
can u provide some info for both units

[RANGER1]

Gorref ,
If there was a blockage surely suction pressure would be low as well.
You stated room temp 20 F & suction of 35psi ( have not got a chart but must be approx 3 F please correct me ) .
Maybe there is high load or compressor problem unless I am misunderstanding something .

[RANGER1]

Like tonyelian suggest condensing unit to small that you installed .

[tonyelian]

hi
tnx ranger1 we arein the same track in that case all symptom point to inefficient condensing unit