Hussmann 2 Dr Frzr Troubles

[daddyfixit]

'96 Hussmann 2 Door Freezer - not cold enough.

Replaced compressor valve plate 2 weeks ago for same trouble (found compressor was slow to pump down - better now. Takes about 10 seconds to reach abt 12 in. vac. and holds when comp is shut off.)

Problem: +4*F Ice cream freezer.
17 oz R-404A (recommended charge) weighed in,
Condenser coil clean,
Evap coil clear,
Pressures with box temp at 40*F, 20/315 PSIG with sight glass flashing (CPR Valve set for 20 PSIG max). (40 min. later)
Pressures with box temp at At 12*, 16/300 PSIG with sight glass still flashing.
Liquid line sub-cooling is abt 5-7*F.

When mist of water is sprayed on cond. coil, head pressure drops to abt 260 PSIG and sight glass clears and is full.

Unit had a 16watt-230vac cond. fan motor. Changed to a 35watt. Head pressure now only about 10 PSIG lower.

Checked SSH, was about 30*F.
Adjusted TXV 4 times to get to about 12* SSH (ran out of time for today - took about 30 - 45 min after each adjustment for box temp to drop back low enough to get a proper SSH reading).

Temp still dropping too-o-o-o slowly. Box has no product in it.

Yes, defrost is working properly as well, not on during cooling cycles.

I don't know where to go next.

[Brian_UK]

What is/was the superheat when the box is at design temperature?

What was the original pull-down time and how does it compare with now ?

[daddyfixit]

The box doesn't come down to design temp. It only drops to about 4*F. Cold control keeps it calling until defrost kicks in. Defrost is working normally.

It acts as though the system isn't big enough for the space. Several thoughts have passed through my empty cranium -
1. What if the compressor has lost its capacity in spite of the higher than normal head pressures? (That is a v-e-r-y long shot.)
2. Is it possible that the evap has blocked tubes and is only half what it should be? (But what of the flashing liquid line sight glass)
3. Can the condenser heat exchanger have lost its capacity even though it is very clean and the fins all look good and secure on the tubes. (I doubt it - it's a three row, one tube coil.)
4. The TXV has gone bad? (Most likely - not looking forward to replacing)

Tackling them in reverse order would be the cheapest. We'll see what the customer wants to do.

Have I missed any possibilities (besides gremlins)?

[philfridge]

[quote=daddyfixit;107507]

When mist of water is sprayed on cond. coil, head pressure drops to abt 260 PSIG and sight glass clears and is full.

[/quote

Hi the problem with the unit I think is that the unit is under condensing I would try to wash out the condenser coil as the head pressure is too high. Or replace it ?

[albionharley]

Hi - what compressor is it ? 12" vac is not particularly good, having said that if the head pressure is high then the comp will struggle to pull a decent vac. When you sprayed the condenser to lower the head pressure did it pull a deeper vac ? If so then i doubt the comp is at fault. More likely as philfridge has said- is that the unit is under condensing. Hope this helps.

[daddyfixit]

Thanks guys. At first, I was leaning towards the condenser too. I inspected it and washed it even though it looked clean and I could see through the fins (no blockages). As I suspected, it didn't help. In the past, I have seen a condenser coil that had corrosion which caused separation of the tube and fins. After a close inspection, this was obviously not the case here. I didn't try the water trick during pump down. Interesting. IF I get the chance, I'll do it.
That's, the problem now. Looks like the customer is leaning towards replacement of the freezer. I hate not knowing, but not enough to shrink my wallet. I'll just add it to the many mysteries of life and try the your tips if I happen across the same thing in the future.

[powell]

Open the CPR all the way, monitoring the RLA as you go. Adjust the charge using the sight glass.

See what happens.

[AOsborne]

'96 Hussmann 2 Door Freezer - not cold enough.

Replaced compressor valve plate 2 weeks ago for same trouble (found compressor was slow to pump down - better now. Takes about 10 seconds to reach abt 12 in. vac. and holds when comp is shut off.)

Problem: +4*F Ice cream freezer.
17 oz R-404A (recommended charge) weighed in,
Condenser coil clean,
Evap coil clear,
Pressures with box temp at 40*F, 20/315 PSIG with sight glass flashing (CPR Valve set for 20 PSIG max). (40 min. later)
Pressures with box temp at At 12*, 16/300 PSIG with sight glass still flashing.
Liquid line sub-cooling is abt 5-7*F.

When mist of water is sprayed on cond. coil, head pressure drops to abt 260 PSIG and sight glass clears and is full.

Unit had a 16watt-230vac cond. fan motor. Changed to a 35watt. Head pressure now only about 10 PSIG lower.

Checked SSH, was about 30*F.
Adjusted TXV 4 times to get to about 12* SSH (ran out of time for today - took about 30 - 45 min after each adjustment for box temp to drop back low enough to get a proper SSH reading).

Temp still dropping too-o-o-o slowly. Box has no product in it.

Yes, defrost is working properly as well, not on during cooling cycles.

I don't know where to go next.

Who cares what the weigh in charge is if you have a TXV.
Back the TXV all the way in and then back it out 3 1/2 turns thats a good rule

I would take out all gas bring the box down to 500 microns and put in new gas. Make sure you add enough to clear the sight glass dont worry about weighing it in.

Check what you got from there

[philfridge]

Who cares what the weigh in charge is if you have a TXV.
Back the TXV all the way in and then back it out 3 1/2 turns thats a good rule

I think that is not a good rule the charge is correct for that unit and messing with the tev is incorrect advice 3 1/2 turns is one turn too much as well .

[AOsborne]

I think that is not a good rule the charge is correct for that unit and messing with the tev is incorrect advice 3 1/2 turns is one turn too much as well .

3 1/2 turns works on all TXV TEV applications when it comes to the valve if you have any doubts you can call sporlan Technical Support or Engineers and they will confirm this. Again it will get you damm close its not perfect but rule of thumb from the engineers.

If you do this and the box doesnt drop down to temp then you have other problems. Weighing in the charge with a TXV because they all come with receivers is pointless because your going to add more gas to add to the receiver

[refmech]

was gas charged in liqid state? this may be the key. 404 does funny things as gas charge.

[hillbillywillie]

check the cond. motor is correct and check the fan blade on the motor is correct and is on the right way.
Make sure cond. is REALLY clean.
I know it's simple-but I've been caught out this way before.

[Gary]

You are missing some important measurements:

The difference between condenser entering air temperature and leaving air temperature (cond delta-T) tells you if you have sufficient airflow through the condenser.

Similarly, the difference between evaporator entering air temperature and leaving air temperature (evap delta-T) tells you if you have sufficient airflow through the evaporator.

[Gary]

I would try to wash out the condenser coil as the head pressure is too high.

We can't tell if the head pressure is too high without knowing the condenser entering air temperature.

[Gary]

There is more to condenser airflow than just a clean coil. The blade must also be clean. The fan motor and fan blade must have the proper rotation. And if the fan blade is mounted backwards it will backhand the air instead of cupping it. Also, the hot leaving air may be recirculating back through the coil.

[R. skiffington]

Hi, Are you sure this is not just a simple case of non condensables in the system? If you have air or Nitrogen in the system it will, generally, collect in the condenser therefroe reducing the capacity of the condenser. It's not not that often you get a problem that's soo technical, if the comps pumping well, the tx valve's working, both coils are clear, then it'll be to do with the ref charge. Cheers