Victory Reach-in Freezer Troubles

[DaHaMac]

First Post, Hi all.

I am a service technician at a college and one of my responsibilities is the cafeteria and all its related equipment. I completed my AAS in Air Cond Tech a little over a year ago and I am becoming more comfortable with Commercial and Residential Air Conditioning. However, I have had not had the privilege to apprentice with anyone on either air conditioning or refrigeration. I have run into some head-scratchers and I am hoping to use this forum as an excellent knowledge resource.

Here is what I've got. The majority of the equipment in the cafeteria is less than three years old and already I am having all types of equipment problems. I clean the condensers three to four times a year, an whenever I work on a piece of equipment. Most all of the new freezer units are 404A and already I have four freezers that have a problem with freezing up the evaporator to the point that the defrost does no good. I would normally expect poor airflow over the condenser or a low charge due to a leak. One unit (which would have been the fifth unit with trouble) did have a leak which I was able to detect and repair. Umm, I'm talking to much again.

Here is the information on the freezer as I took it earlier today.
Ambient Air 77F
Entering Cond. Air 75.5F
Leaving Cond. Air 80.7F
High Side Pressure 205psi (~135F)
Low Side Pressure 5psi (~-5F)
Liquid Line temp 80.3F
Suction Line temp 56.2F
Evaporator Temp 3.3F (Evaporator was iced)
Box Temp 14F
Supply Air Temp 29F

Two days ago I recovered and recharged the system. The system is a 404A system using two Cap tubes and has a CPR valve (which I had no idea what it was until I started reading this forum). The defrost timer appears to be operating and it is electric defrost. I have four pegs on the defrost timer, so that it will defrost every 6 hours.

I'm not sure what to do next and any help will be appreciated. I am not ashamed to admit that I am still a bit of a rookie and I don't work on this everyday as my job requires me to be a jack of many trades.

Thanks,
Daniel

[refertecbd]

Force a defrost a check amp draw of the heaters. You might have a problem with a defrost control or the heaters them selfs

[iceetech]

first thing i would do melt all the ice off evap coil and then take the readings and temps. Next thing is check defrost operation. put your amp meter on #3 or n-o contacts on defrost timer and put that timer into defrost.make sure your pulling amps when you put it in defrost. sometimes the defrost timer contacts will stick or weld shut and will never go into defrost even though your timer says that it is. hope this helps

[hvac wiz 79]

de ice coil .. observe pressures upon start up to ensure you dont have a restricted cap tube

[frank slusher]

check the defrost termination/ fan delay switch. also make sure the evap fan comes on and stays runnig when the door is closed. door switchescan go bad or the door can drop as box pulls down. seen units where the hinges are out of alingment cause this problem, sometimes the switch heats up and the fan drops out.
tough to find short of climbing in the box and watching. cuase how do you really know if the light goes off when the door closes.

[chefid]

watch the people use the units maybe they hold the doors open to long. are the units under a hvac vent? if it is multiple units in the same place it seems like it is probably user error not problem with system. what is the room humidity?

[mcr]

watch the people use the units maybe they hold the doors open to long. are the units under a hvac vent? if it is multiple units in the same place it seems like it is probably user error not problem with system. what is the room humidity?

Had the same type of problem with a produce cooler. Clowns would walk in, get what they need and not close the door behind them. That plus a t-stat set a tad low would cause the evap to freeze. A tweak with the stat and new hinges with springs solved that problem. Now I got a Carter-Hoffman air curtain reefer that freezes up. Checked all the usual things as far as the refrigerant circuit. Come to find out the digital control says it's 38º and shuts off,but in actuallity it's -2º. I was wondering how ice could form on the outside of a refrigerator. Big bucks I think for control.

[DaHaMac]

Good ideas so far.

I really appreciated the information on how to check the defrost controls, little things like that really help in troubleshooting. The next opportunity I get to look at the unit I will check the defrost as suggested.

I have defrosted the coil and checked pressures on start-up and I found that the pressures do not equalize between the high and low sides. I should have included that tid-bit in my first post. The high side reading corresponds with the 404a at room temperature, but the low side pressure corresponds with the 404a being well below freezing. Would the CPR act as a restriction?

I did a pressure test with nitrogen, and the nitrogen equalized fairly well between the high and low sides.

I do not believe this unit has a door switch for the fan as the fan continues running when the door is open.

The room conditions are not the greatest for this one freezer because it sits next to the deep-fryers in the cafeteria and I have had nightmares with trying to get the condenser coils cleaned.

I'll do my best to keep the thread updated as I learn more. The challenge of my job is that I often don't get to stay continuously on a project until it is completed. Today I have been creating designated cores for Best locks and trying to get a sewer snake through a clogged drain. Of course, I rarely get bored.

Later,
Daniel

[DaHaMac]

Well I checked the defrost and the defrost heater is indeed pulling amperage.

The high side read 150psi when defrost started and after about five minutes the high side pressure slowly dropped to 100psi and then began to rise again. I returned the unit to normal service after about fifteen minutes of defrost. The low side was steady at 33 psi during the entire time it was in defrost and when the unit returned to service the low side slowly dropped to 5 psi.

The digital thermometer was reading -56F, but of course that is wrong. It seems that the majority of the digital thermostats in the Victory units are worthless. The NSF thermometer hanging on the rack was reading about 20F, not quite cold enough.

[hvac wiz 79]

here is a good link engineerdave put in another thread that explains CPRs http://www.sporlan.com/90-11.pdf
.. observing the pressures, did the suction drop basically right away to 5 psi ? did the head also drop as the suction did ? im still thinking restriction .. but playing swami is something i am not good at

[DaHaMac]

here is a good link engineerdave put in another thread that explains CPRs http://www.sporlan.com/90-11.pdf
.. observing the pressures, did the suction drop basically right away to 5 psi ? did the head also drop as the suction did ? im still thinking restriction .. but playing swami is something i am not good at

Yesterday the suction pressure slowly dropped to 5 psi on start-up, the suction line from the compressor to the CPR valve frosted over until 5 psi was reached and the condenser pressure immediately went to 200+ psi.

I caught that thread about the CPR valve and have already printed the material. This forum is a good resource for information.

I am honestly leaning to a restriction in the cap tubes myself. When I first charged the system after defrosting and evacuation, I noticed that the cap tubes were freezing before they reached the evaporator and the evaporator froze in the first circuit.

How do I definitively know that there is a restriction in the cap tubes? I can vaguely remember something from school on the simulator about checking the temperature across the cap tube. Unfortunately that was on the computer and not on an actual piece of equipment What should be the maximum temperature drop across a cap tube in a freezer? IIRC, isn't it 3F for an air conditioner?

I know that they are a lot of variables due to differences in equipment, but what sort of pressures ranges should I see in a normally operating 404a freezer system. I know that the suction pressure would have to correlate to an evaporator temperature below the desired freezing point. So if I needed to maintain -10F should I allow of a 10F to 15F delta T across the evaporator and conclude that my operating suction pressure should be equivalent to the pressure for 404a at -20F to -25F?

If that is true, what should my condenser pressure be running? In a freezer will it be running cooler than what I would expect in an R-22 air conditioning system? IIRC someone told me on an AC system to expect the condenser temperature to be 20F to 30F higher than ambient. Does this rule of thumb apply to freezers?

I would love to have a service manual from Victory for these units, but I did not see one offered on the Victory website. I guess I could try and see if our parts supplier can get me one, and then get the approval for a requisition (working for the state is fun when it comes to getting tools, parts, and etc.).

Enough questions for now, my newB status is clearly showing through

[the mojo]

So those cap tubes are giving you fits,eh? 10' of .036 X 2 with a new Sporland 032Capt filter a sweep or 2 of nitrogen and a evac to 250 mikes. A fresh balanced charge, a 10-12 lb setting on that CRO4 and you'll get your answer on what the head will be.

[r404a]

Sir,
I had a call on a box like this , when 404a was just making its mark and arrived just after the maintenance crew clean the coil. In any event, the readings were very similar and since you have access to this box (ie no charge, per se) it may pay dividends to do this: Pull the gas. If you did, did you weigh it? With the subcool you got, proably had name plate charge in it. Next, carefully cut the copper line with an imp cutter, where the cap tubes join the drier outlet. The goal here is to observe the cap tube inlet, each of them, to see if you have any sludge in them. 134a and 404a are notorious for captube clogs with condensers that are allowed to get dirty. The heat can cause issues with sludge and you can end up with a scenario as this. If you are the tech that PMs this unit, and your coils are clean, have you lost a fan motor on the condenser at some time? SWame effect. Good luck and we are glad to have you here at HVAC Talk.


r404a