Display case cooler help

[Derek]

Hey guys, I'm helping my boss out with a problem with his waitress station/display case cooler (it cools lemonade, milk, iced tea, etc. and has glass sliding doors on it) but have run into some problems...

Just some background information: We started with a 20 year old compressor that was shorting to ground, so there was line voltage between the case and ground. I replaced the compressor with a 1/2 h.p. rotary compressor and condenser from a 5200 BTU a/c unit.

The compressor/condenser is about 15 ft away and in the basement, the suction line is 1/2" and insulated the entire length, the liquid line is 1/4". The old system was charged with 401a before I disassembled it. It was electrically run via a suction line pressure switch and a timer.

The evaporator is ~ 10" x 10" x 2' in size and has a TXV with the bulb obviously attached to the suction right after the evaporator.

I also removed the suction line pressure switch and timer and installed a thermostat switch to control the compressor, shutting it off when the temperature in the cooler reaches 38F.

I recharged the unit after vacuuming with R22 and was going to charge based on superheat at the suction line but regardless of the amount of charge I give it, the suction line pressure remains ~ 50 psi and though the evap is getting cold the suction line at the compressor is almost room temp, resulting in an overheated compressor which shuts down in 5 - 10 minutes. The old compressor didn't have any over temp protection so I'm assuming that's why it eventually failed.

There is a liquid sight glass on the high side, no bubbles in there btw.

I know this isn't computer related but all the HVAC forums out there are VERY non DIYer so I wanted to see if you guys could help me out here. My boss wants me to figure this out as he's always been a big DIYer and considers this a learning experience for the both of us.

Thanks ahead of time,
Derek

[[XC] 2long4u]

Wow long time no see.
Sounds to me that the TXV is stuck open. That will result in the high pressure on the low side.
What was your high side pressure when you were charging it?

[Derek]

Only had one spare access valve when I first tried charging it, so I don't know high side pressure but since then I've added one. When I charged it the liquid line was fully liquid (no bubbles in the bubble window). I'm assuming since I was charging for suction temp I got too much refrigerant in it waiting for the suction line to start cooling. I Don't want to waste any more R22 seeing what the high side would be though.

If the TXV were stuck open it still wouldn't fix my main problem which is little to no suction line cooling for the compressor would it?

My boss has a cylinder of 401a that the previous tech left a long time ago by accident. This stuff is supposed to be a drop in replacement for R12 (the original refrigerant in this whole system). I'm thinking of vacuuming everything down and charging with the 401a to see if that fixes anything though I doubt it will. I also think I might try R290 just for s and giggles. It's certainly cheap!

Simply put, compressor cooling via suction line is the number one concern. I'm guessing this from too long (or too poorly insulated) suction line and/or incorrect or broken TXV. I honestly don't know what to do in this situation but I need to get this thing running ASAP.

Wow long time no see.

Yea I'm definitely a lurker. I don't post unless I can't find the information by searching the forums/internet, which is basically 99% of the time.

[[XC] 2long4u]

You say there is no bubbles but is it condensing? Or is there no bubbles because it is all gas?
I would get some insulation for the suction line and see what happens. But I don't think a suction line could absorb that much heat.

[Derek]

As I charged I slowly watched liquid show up in the glass and then eventually instead of liquid slowly spewing through it was mostly liquid and a few bubbles and then all liquid no bubbles.

Suction line already has insulation on it, but not a great deal. I have to crawl through a VERY nasty crawlspace (lots of spilled grease that finds its way through the floor from the kitchen area, TONS of cobwebs, etc.) to re-insulate the suction line. The building is >100 years old so the crawlspace where the suction line goes through is just dirt with very old stone walls for the foundation. We call it the dungeon at the restaurant as there are basically trenches dug in the crawlspace to get around some areas, but no trenches where the suction line is. The condenser/compressor/etc. is all located in a mostly finished off part of the basement with cement floors.

[wdrzal]

Sounds like you have to high superheat, sounds like the evap is not getting flooded with enough refrigerant(starved). You charge txv by subcooling or sight glass, you charge should be ok as long as you didn't over charge causing excessive high side pressure,as there are no bubbles in the sight glass you have enough refrigerant. you need to determine what the superheat is.Did you try adjusting the txv for a lower superheat(lower superheat will give you more compressor cooling). you changed refrigerants you may have to change the orifice . The p/t charts for r401 and r22 are obviously different. but 22 will work in a med temp system. and the pressure ratio of the compressor you removed and the one you installed will also be different. Of course all this is mostly assumptions made from what you said.....


Why didn't you just put in another piston compressor(I'm sure thats what you removed) the same size/type and charge withe the same gas since you have it ?????? simple.......


Just for Giggles:....... Even thinking of R290 is illegal in the USA......if the evap would leak and just turning on or off the case light ,or any other ignition source inside the cooler could blow the cooler apart. You created a bomb and will be held responsible for for doing it.

[DetroitAC]

I think your problem may be the TXV/refrigerant mismatch. As Walt said, the properties of R22 and R401A are very different. A TXV is a pressure balanced creature that contains a mixutre of refrigerants sealed in it's power dome that works well with the refrigerant being used. I think you have a TXV that was designed for R12 and now you're using R22. R401A is close enough to R12 that it's considered a "drop in", R22 is not. I'd guess you need to either change the TXV to an R22 model (properly sized for the capacity and application), or use the 401A.

You didn't say what the compressor was that you replaced. Were you unable to identify it? Walt is right about that part too, easiest thing is to put the same size compressor in there, it was already matched to the load. If your new compressor is too big, that won't be a good thing. What was the timer for? Was it an anti short cycling arrangement?

[[XC] 2long4u]

If it originally had R12 you could also use R134a to get similar results. R134a is cheap enough to give it a shot.
Walt I did some research and R290 is illegal in automotive applications but it can be used in refrigeration systems.
Edit: R290 is almost exactly like R22 so if you are having problems with the R22, R290 won't help.

[Derek]

The old compressor was from the 70s (I guess it was older than the 20 years I originally stated), and there is no information I was able to find on it as the nameplate and such was corroded off from years of moisture and dirt so I don't know much about the original compressor other than the windings were grounding out and it was making a constant clacking and knocking. I'm guessing it was between 1/3 and 1/2 h.p. piston type compressor. The reason it was replaced with a rotary is because of how easily the rotary was bought -- it came in an AC unit. I would have to ship anything else in as the only other refrigeration store in my area got flooded (I live near Cedar Rapids, Iowa). I don't think the 1/2 h.p. rotary is oversized but I'm no expert so I might be wrong here.

I looked at the TXV but I didn't notice anywhere to make adjustments on it. I think I will look again though. It has one inlet and one outlet, not including the capillary tube with the bulb on the end of it. I can't say I have any experience with TXVs but I do understand the principal behind them.

I won't be using R290 (it works the same as R22 anyways as a couple people mentioned). I agree with you guys, too dangerous and though I'd do it for my own system I wouldn't charge it on someone elses.

The timer was a band-aide. The previous tech installed it to solve problems with the evap freezing up according to my boss. He just told me this today. I don't honestly know how the electrical side of the old compressor was hooked up with a low pressure switch turning the compressor on and off and the timer keeping it from running for too long. I started trying to figure it out but it was just a mess of wiring. I replaced all of the wiring/electrical with a simple thermostat switch turning the unit off when the waitress station reaches 38 degrees since it seemed like a simple and effective solution. I replaced the condensing unit to his walk-in cooler with a very large window ac last year and switched out the thermostat and it's working better than the old unit had ever previously.

Since I'm pretty sure the problem is with the gas mis-match I think I'm going to charge with the 401a today and see what I can figure out.

Thank everyone you guys are fantastic!

PS - my R12 needs recharging on my car, would 401a work? It looks like it's mostly R22 but I could toss in a bit of propane to make sure oil would travel with no problems. It appears 401a is a good replacement for R12 in a lower temp situation...

[Derek]

Sounds like you have to high superheat, sounds like the evap is not getting flooded with enough refrigerant(starved).

Just out of curiosity... How would I have problems with not enough refrigerant in the evap when the suction line is showing such a high pressure? I guess this should be pretty simple but it's just not making sense to me. I don't doubt you in the least but would appreciate an explanation of why this would be. I guess I'm used to captubes where not enough refrigerant in the evap coincides with low suction pressure.

[wdrzal]

If it originally had R12 you could also use R134a to get similar results. R134a is cheap enough to give it a shot.
Walt I did some research and R290 is illegal in automotive applications but it can be used in refrigeration systems.
Edit: R290 is almost exactly like R22 so if you are having problems with the R22, R290 won't help.

http://www.arti-21cr.org/research/co...s/50025-es.pdf

[Derek]

Alright so evidently I don't have any R401a... My boss told me about the 30 lb cylinder but it's empty. =(

Charged with R22 again and I watched as it seemed to be working at first, but then the high side pressure got really high all of the sudden and the compressor overheated and the unit shut down. The suction line still stayed at around 40-50 psig throughout the process of the high side going up.

I'm doing a triple evac each time I charge this thing so I really doubt there is moisture in the system. Plus if the TXV clogged wouldn't the low side pressure become very low as the compressor draws a vacuum?

There isn't much air going over the compressor as it is right now, but should that make a huge difference anyways as far as compressor cooling? The condenser fan pushes air through the fins instead of pulling, and the compressor is on the fan side of the condenser so it just has air being sucked across it.

[Derek]

Just took another look and the expansion valve is an Alco HF 1/2 FC.

Looks like a 1/2 ton expansion valve and there is a place to adjust it on the bottom. Which way should I turn it and how should I tell when it is set to the correct place?

At this point I have to use R22 since I don't have any R12 and the R401A is empty. If I need to buy a new expansion valve that's fine but I will need some help selecting it.

The expansion valve itself seemed pretty cold (there was some frost on it) but the evaporator wasn't cold. This makes me think moisture or clog but once again I vacuumed the hell out of this thing so I just don't see how that could be possible. Maybe I'll evacuate the current charge and triple evacuate it again.

Update -- did some research, the HF series seems to be correct, the 1/2 would be the correct tonnage (I'm using a 1/2 hp compressor from just under a 1/2 ton air cond too, that should work fine), and the FC denotes it's for R12. Is this expansion valve going to be able to be used with R22?

[[XC] 2long4u]

No. Use R134a. It is super easy to get. You can get it at Walmart or any auto parts store.
With the high side pressure going to high the condenser might not be able to handle the R22. R134a is a lower pressure gas then R22.
R134a will work great for that application. Just make sure you used Ester oil.
R134a is to R12 as R290 is to R22.

Walt what would be considered "Industrial"?

[DetroitAC]

Derek, If I were in your shoes, and with the budget that your boss apparently has, I'd look for R12 on ebay. You can get it in sealed automotive cans, so you know it's virgin stuff. Pick up some for your car too.

Update -- did some research, the HF series seems to be correct, the 1/2 would be the correct tonnage (I'm using a 1/2 hp compressor from just under a 1/2 ton air cond too, that should work fine), and the FC denotes it's for R12. Is this expansion valve going to be able to be used with R22?

Sorry, it won't work.

You say the low side is running at (let's say 45 psig) with R22 the saturation temperture will be ~22F. Frost makes sense at the TXV.

Your TXV is seeing 45 psig, and let's neglect the capacity influence on superheat and assume that the TXV will hold a constant 10F superheat at evap exit. That means the TXV will modulate to hold the evap exit gas at 59F.

OK, 59F evap exit gas temp, with 22F evaporating temperature means that the TXV will try to hold 37F superheat when used with R22, even though it might be set for 10F superheat with R12. (FYI 37F superheat is starving the evaporator, and the first few passes will likely ice up slowly until the entire core is iced up)

If you tried to back off the superheat bias screw, you would make the TXV believe that the evap is flooding long before you got an acceptable operating superheat.

R22 TXVs are cheap and plentiful, since it's being phased out. You could get a proper TXV and that would solve this problem.

R12 is not very expensive, you could buy some R12, keep the TXV, and that would solve your problem.

[Derek]

I used the last tiny bit of r401a and then r22 and backed the screw way out on the TXV and it is acceptable now. I think I will get a replacement TXV in the future but for the time being the compressor is not overheating, the evaporator is cooling well and the display case (with the thermostat turned all the way down) has gotten below freezing. Superheat is a bit high so the compressor is running warm but it's not tripping the overload so I think I'm good to go. Evap has frost all over it too.

Thanks again for the help everyone, couldn't have done this otherwise.

BTW - high side pressure is ~ 175-200 psig and low side with the screw backed out all the way is at 20-35 psig.

[[XC] 2long4u]

I'm glad it worked out. Don't be such a stranger.

[wdrzal]

You really need a r22 TEV @ needed capacity which will have the correct bulb charge gas & spring that balances against system pressure. IIRC 22 is 50psi higher than 401 at ambient(where your stating out from. That will slam your current tev shut,thus the condition you described.

A frosting evap (forced air evap,I assume) is no good in your application. too cold and the coil will ice over and with no defrost mechanism you will lose cooling capacity and the compressor will run and run trying to satisfy the thermostat you put in the case. You want the low side pressure set high enough so the coil doest freeze up in the refrigerator case.


edit: LOL: I scrolled over and didn't even see Detriotac post 15 to after I posted,haven't slept since sunday........

[wdrzal]

No. Use R134a. It is super easy to get. You can get it at Walmart or any auto parts store.
With the high side pressure going to high the condenser might not be able to handle the R22. R134a is a lower pressure gas then R22.
R134a will work great for that application. Just make sure you used Ester oil.
R134a is to R12 as R290 is to R22.

Walt what would be considered "Industrial"?

To tired to type > than 1,000,000 words........In commercial & industrial your can always produce professional engineering designs and submit them to the proper Federal, state and local regulating agencies (sometimes there may be 1/2 a dozen agency's that have a say) and ask for "variances" to deviate from mentioned codes. The more stringent always supersedes.Their engineers will review the request on a case by case basis. This can be a long and expensive process. You need a good reason and a safe design to get a "variance" from most of the codes in place written by the various engineering society's in the USA.

Engineering practices and codes are in place for a reason,mainly to protect the public. Your surrounded by vary dangerous items in your daily life. It's the job of engineers that these items operate so safely the danger mostly goes unnoticed by the average person........

So, it best to follow the combined accumulated knowledge of published engineering practices & codes.As I stated before many codes and practices are to ensure a device works as intended and poses no to little risk of a failure.

While experimenting is fun, experimenting building a new skate board doesn't have the same scrutiny & potential for catastrophic failure as say building a pressure vessel filled with a refrigerant that contains lots of chemical energy .......

[captaincascade]

im asuming this is a 4c box. In that case if the unit starts to ice up, its simple enough and cheap enough to wire an off cycle defrost. An off cycle defrost is where the compressor is left off for an aloted amount of time leaving the evaporator fans running. On a standard 4c box with a forced air evap this is the norm for ice problems. just make sure your evap fans arent wired to run only when the compressor runs.

the way the tech had you low pressure switch wired wired: he had a on delay timer wired in series with the low pressure switch so that when the low pressure switch closed this timer would begin its timeout, maintaining an open circuit to the comp,. after set time, the compressor clicks on. This has the same affect as an off cycle defrost.

If your metering device isnt metering properly. In this case not enough restriction. Your head pressure will be low and your suction high. It'll barely pick up any heat because the pressure difference isnt great enough for the refrigerant to boil. typicly you need a minimum differential of 100 psi for any real cooling. that compressor was just moving aroud some liquid and choking on its own heat.