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k thanks for all the help. the unit i worked on today coincidently had a headmaster.... i have questions on that but a bit off topic and don't feel like quizzing you guys the rest of the night lol

The control probably has a minimum differentila of 40-60psi so if 196psi is your target, it should be somewhere in the middle. You would set the control to CO at 180ish CI 220-230ish. Doesn't need to be exact. A headmaster is a more efficient way to control liquid going to the txv

I understand that when the control reaches a certain pressure(high event), it turns the fan on, and when the pressure drops to a certain point(low event), it turns the fans off. i get that part. what i don't understand is how you arrive at those set points

appreciate all the help guys. back to the fan cycle control question though, say you're using r-22, looking for a condensing temp of 100*f, you're saying use that, converted to pressure(196psig), you want to use that as number as your differntial? and what would you set your high even at 200*f? A bit confused

It's called job security

let me rephrase that. My senior tech. And yes,,, I like to work too.

I just hate cleaning up messes left by my "senior" tech.

Glad to help. I'd be a terrible boss though. I like to work LOL

just for the fact that I read your posts. If I every was in a bind I knew I could call you and you would give me information that would actually help me.

Oh?
please explain

2sac,,,,, I wish you were my boss

Rule of thumb for a defrost clock. 4 defrosts per day timer on clock should be set for no longer than 45 min BUT you should have a temperature termination switch on the coil. The timer on the clock is usually used as a backup method to terminate the defrost.

Food takes along time to thaw.

As far as the LPC, What is ts purpose? A safety? A temperature control?

Fan cycle control? Doesn't matter what referigerant is used. Time to pull out the PT Chart. You're in A/C, What condensing temp is ideal in a properly charged running unit under "ideal" conditions? Compressors are designed to work to their potential under these conditions. It's an easy answer. Anyway, that # should be in between your cut in and cut out of the control.
Hope this helps. Can't get into too much detail on an open forum.

EDIT If the defrost os too long, water droplets will form on the top and sides of the box and then freeze

-2sac said what's wrong with ice on the txv. I've read that if there is water in the refrigerant (say on the first hot day, drier turns a drop or two of water loose), it will freeze in the expansion valve, and stop the refrigeration circuit. mis-understood sentence and interpreted it as ice on the txv indicates moisture in the system. after further reading, i understand that its moisture IN the refrigerant that will stop the expansion, not ice ON the txv.

-what is the general rule of thumb for setting a defrost clock, and what do you do if unit is still not defrosting properly? Do you add 5,10, or even 15 minutes to that defrost cycle? There is no rule of thumb per say. It all depends on how the customer uses the box. D

- If you lengthen the time of defrost, do you have to worry about perishables thawing during that time? does anything need to be adjusted as far as low pressure controls?

-how do you properly set a fan cycling control? (and for learning purposes we'll say with an r-22 system)

For defrost it all depends on how often the door is open. Customers will always tell you that they close the door but you will find out with time that everyone LIES! Depending on the conditions at the store you may see a unit in that only defrosts 3 times a day for 25 minutes. That same unit in a humid environment will need four. Don't consider the job done till you check up on it. I don't know how many times I go to a job at a local fast food place and arrive and see that the freezer door is propped open while they do inventory. Leaving a freezer door open in North Carolina in the summer times will frost up an evap in no time. You have to adjust and modify accordingly.

For the thawing,,, I say no. If you box is down to temp the effects are negligible. Of course if there is a deforst going on and they leave the door propped open you may have a problem. It all depends on the environment

For fan cycle switches set them to simulate a 90 degree day. Ignore the gauge on the low pressure switch. Always use your manifold to set em. May take you a lil while to get it figured out but once you get the first one you will find that the rest are a breeze!

Just a thought, don't be afraid to leave an invoice open. It gives you the chance make sure the changes that you have made are correct and working in the customers best interest.

Found settings on defrost clock to be adjusted improperly, as well as the fan cycling control. Found my low side gauge to be faulty and replaced with new one. subcooling was around 7*f and superheat around 30*f. added some refrigerant, adjusted settings of defrost timer and fan cycling control and unit is operating properly at this time. Unit did pump down, and to rephrase the unit going into defrost 3 times, i meant that the cond. fans went on and off 3 times within the couple hours i was there. My boss told me to check the settings on the fan cycling control, defrost timer, check for restrictions in the line, and charge. found no restrictions, or temperature differences in suction or liquid line, and issues listed above were corrected with the bosses guidance.

Questions/ Concerns at this point are:

-2sac said what's wrong with ice on the txv. I've read that if there is water in the refrigerant (say on the first hot day, drier turns a drop or two of water loose), it will freeze in the expansion valve, and stop the refrigeration circuit. mis-understood sentence and interpreted it as ice on the txv indicates moisture in the system. after further reading, i understand that its moisture IN the refrigerant that will stop the expansion, not ice ON the txv.

-what is the general rule of thumb for setting a defrost clock, and what do you do if unit is still not defrosting properly? Do you add 5,10, or even 15 minutes to that defrost cycle?

- If you lengthen the time of defrost, do you have to worry about perishables thawing during that time? does anything need to be adjusted as far as low pressure controls?

-how do you properly set a fan cycling control? (and for learning purposes we'll say with an r-22 system)

Now we know it's hot gas defrost. If you know how hot gas defrost works. You should be able to determine if this is the problem or you need to look elsewhere

Originally Posted by akerilla

system is r502, 3ph, 208/230vac.

I'm thinking its one of these things:

1) low on refrigerant (didn't want to jump to conclusions because i knew super-heat/ sub-cooling would be off with unit frozen. wait till tomorrow to check)
60psi suction? You think this is low?
2)moisture in refrigerant, plugging txv and thats why that side is icing up. need to recover refrigerant and replace with virgin refrigerant
60psi suction? You think txv is plugged?
3) Txv going bad, losing thermal charge
Txv losing charge? How long does it usually take for a powerhead to lose its charge?

4) bad pumpdown solenoid
60psi suction? You think the pumpdown solenoid is bad?
5) bad compressor valves which indicate high back pressure?
-with this, would the compressor be drawing high amps?
Why would you have excessive amps?
6) fan cycling control binding up? i don't see how that could do it though. the compressor would be sending hot gas thru the evaporator essentially keeping it in the defrost cycle, right?
180psi head? You think fan cycle is binding?
I have 5 yrs experience installing furnaces, a/c/ and ductwork, but I'm new to servicing refrigeration so help would be appreciated. Thanks for any and all help.

So let me get this straight. No ice on the coil when you arrived. Box @ 0-2 degrees. Was this temp measured with the box thermometer or your digital? Unit ran for 1/2 hour while you checked electric and now you have ice around txv. Was there ice around txv before this? What's wrong with ice on the txv? Did you check? Pressure dropped and unit went into defrost and cycled fan??? 3 times? This sentence makes no sense, please rephrase it.

This is a freezer, not a cooler as you originaly stated? What type of defrost? Does it pump down?

Think about all that was said. Let us know what you found.

its a hot gas defrost system. and it was only the side of the expansion device and pump down solenoid that was iced up, not the entire evaporator coil which is what lead me to believe that it could be a problem with the txv or there could be moisture in the system. as i said im going back today and will find out and let everyone know. thanks for all the advice

Make doubly sure you have cleared all the ice of the evaporator coil. Get your flashlight and check between all the fins all the way through the coil. Iced up refrigeration coils can be clogged with ice and it can take awhile to get it all melted.

Sent from my Transformer TF101 using Tapatalk

Your choice of words maybe in correct.

You talk about "defrost" happening all the time. Cycling on and off should not cause the evap to go into defrost. Are you sure that you are introducing heat required for defrosting?

What type of defrost is it, electric, hot gas, reverse cycle!

If the room temp rise then your load rise and you will get high suction pressures. You indicate that the suction pressure drops then goes off. So the comp does seem to be working.

If the end tubes are frozen (and happens over along period) it could be that the expansion valve bulb is covered in an ice ball, causing the TXV to act strangely (not common but no unheard of).

Clear all ice first! A clean start.

Start the system with out the fans running (keeping a eye of the system) You should see the suction pressure drop and the evap freeze evenly.

If this happens then, we are moving in the right direction.

Now reconnect the evap fans, we would expect to see a high suction and likely high superheat, the room should fall in temp quite quick (if empty and limited load), when are getting closer to the desired box temp, the evap pressure should fall along with the superheat becoming under control.

If this is all OK, then you need to investigate the controls,

thanks for the info, much appreciated. the ones that i have worked on with the senior tech in particular were bad burnouts, and we installed the HH style drier. back to the compressor though, would superheat solely indicate that there is compressor trouble?

on bad burn outs...suction line driers are for clean up ...not meant to be left in system permanently