Using a low pressure control to control box temp, this was a service call on a Delfield reach in that was freezing the product. I found that the low pressure control was not set properly and this was allowing the unit to get to cold.
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So we've got a system here where the pressure control is out of adjustment and it was freezing product last night and then now it's not working at all and what's happening is the coils all frozen over, so we're gon na get it defrosted real, quick and then We'll go through adjusting this pressure control and getting it set right. So, while I'm waiting for this unit to defrost, I want to point out. This is in fact a newer unit. It's probably eight years old.
It's got a new coil in it, but it does not have any temperature controller on it. It's literally controlled temperature just by a pressure control, so we've got a coil, a condensing unit, a pressure control and that's it. What I did right now, just so that I can turn the fans back on was I disconnected one lake from the pressure, control and taped it off, but you see there's no solenoid valves, no anything so we're just simply going to start with my cut in temperature. On the pressure control and then work our way back from that and we'll get into it a minute, so it didn't take too long.
I went ahead and got this guy to defrost itself. I just left the fan. Do it maybe eight ten minutes, some like that? So I'm gon na go ahead and put back together. I just opened it up to verify.
There was nothing on the coil there's not you can see. This is a brand new coil, so we just need to make some adjustments to it. So I've started the system up started with my cut in pressure, which is gon na be in the babies. I took my pressure chart and I found 39 degrees.
That's what temperature I want. This system to turn back on at is 39 degrees. So then, I set my cut in on my pressure control at 39 and I will adjust the differential or the cut out as I see fit, while watching the bumps run. Okay, the box is running right now, 58 degrees in the lungs which is watching anything ugly.
So the unit's running is coming down in temperature, see my box temples at 41 degrees right now. Let's return our town we're running approximately a 20-degree on the evaporator TV, that's the temperature difference between return, air temp and the vapor saturation temperature, it's approximately 20, and we're just waiting for the box to satisfy. So you know this is not a race we're gon na watch. This thing cycle on and off the two to three times, because we're gon na get the perfect setting on it.
I'm guesstimating that our cutting is going to be about 85 and our cutout is gon na be about 45 by Ilana we're just waiting to see. I want to point something out on these little regions. It's very hard to use super heat because of a couple different things, but the one biggest thing is is they're running the suction line in the liquid line in the same set of insulation. So Super T it's going to be a difficult number to diagnose on, though you can evaporate or superheat there's really nowhere to grab, because they don't give you any space so a lot of times in reach and refrigerators.
It's you're lucky if you can actually measure superheat in a good place, but even still, I'm clamped on, like they're, now granted that's running with the liquid line. So that's absorbing heat from the liquid line. All the way from you know through that line set right there, but I'm still doing pretty good for compressors to breathe, I'm at 33 degrees. So we're looking good right now, we're running a 20 degree TD, we're just watching the Box come down to temperature. It's at 37 degrees, LOX, temp right now, everything's, looking good. My liquid saturation temperatures drops more than 30 degrees above my ambient, so you know we're looking good so far, just trucking along just wait for it to come down. Temp, it's just a rating process, so we just cycled off 35 degrees, 34 degrees right in there pressures at 66 and we're just gon na watch. It turn back on and see where it turns on and off at and monitoring the temperatures.
Okay with some tweaking, I got this thing set where I wanted it to just some fine-tuning adjustments. So I use those initial numbers like 85 and I think I said 40 something just to get me in the ballpark. And then I tweak the numbers here and there to get it dialed in so on my thermometer right here. My max temp is 40 point three.
My minimum temp is 34, so I bring my box temp down to 34, but then back up to 40. That's perfect! That's the perfect setup, that's the most most split that I want to put between there because I go any colder and I'm gon na start risk freezing their products because that air blowing off the coils a lot colder than 34. So we don't want to freeze their lettuce or anything so yeah, that's where we're at and I'll explain a little bit longer! Recap! Okay! So let's do a little recap here we had a service call on a delfield refrigerator that wasn't working properly. Okay, this one is a little peculiar because they're actually using a low pressure control as a temperature controller.
For this unit there is no cylinder and there is no electrical mechanical or digital temperature controllers whatsoever, so they're simply monitoring the box, low side pressure and they're using that to cycle on temperature. Okay, I recently did a podcast with Brian or on HVAC school talking about reach and refrigerators, temperature controllers, and we kind of covered this a little bit. I also wrote a tech tip on his website also about the same topic and that's of using a low pressure control as a temperature controller. Okay, it's not a very common thing anymore, but I do occasionally run into it.
So this one's pressure control was actually out of adjustment, so the pressure control was making the Box get too cold and it caused the evaporator coil to freeze up, I defrosted the evaporator coil, and then I went to go about adjusting the pressure control to the right Temperatures and pressures: okay, the way that we did, that was, we started with our cut in temperature. Okay, I knew that I wanted this box to turn the compressor back on when it got to around 40 degrees. Okay, so I found a temperature pressure chart. I looked for 40 degrees Fahrenheit and I read the refrigerant refrigerant type and I read down the line and found what pressure that refrigerant would be at 40 degrees, and that was my start point. Okay, once I did that I let the Box cycle and then once the box got down to temperature, where I wanted it, which was about 34 degrees. I noted what pressure was an digested, the pressure control accordingly for the cut out pressure. Okay, then, it took a little tweaking to fine-tune it in between there, but it is important to know that we do still run into these kind of systems - it's kind of antiquated, but it actually is very effective. Just like a constant cut in control, because it's pretty much well, it's doing a pretty good job, not as good as a constant cutting control, but it'll help to make sure that there's no ice buildup on that coil now, a constant cutting temperature controller would work better Because it's actually embedded in the coil and it's sensing, the physical coil temp versus the actual pressure in the system.
So, theoretically we could still have some ice on the coil and our pressures would be enough to turn the system back on. Okay, but that's pretty much. It it wasn't too difficult, but I know this can be very confusing for people. Okay, hey! I just want to say thank you guys for taking the time to watch my videos.
I really appreciate the feedback you've been giving me. You know leave me some more notes. Let me know what you think. Let me know your questions, video topic, ideas and, as I've mentioned in other videos, I'm really looking for new service technicians right now, I'm willing to train or I'm willing to hire someone with experience.
So, if you're interested in working on the kind of equipment that I do hey, send me an email, hvac our videos at gmail.com or that's also down in the show notes of the video and I'd love to look over your resume. Okay, thanks a lot and we'll see you guys on the next one:.
Hi Chris . Would that scenario be also called an Off cycle defrost ? Just started doing my level 1 for rerigeration at school . even though I have all my hours to do all 3 levels , Im just finally doing my schooling after almost 7 years doing HVAC . Service area Barrhaven??
Thank you for a great video,,, how did you decide on that temperature range, I know most region refrigerators have a box temp of 40 but how did you decide on descending to the temperature of 34 as your cut out temp. Many thanks
Nice job, old school temperature controlling. Well done
Phenomenal information thank you
Question. cut in pressure, So if pressure isn’t up to what the cut in pressure is set to the txv won’t feed refrigerant?
Wow, dejavu from the seventies, , spent the first two years of my apprenticeship building those things, except we mounted the evaps on the roof of the cabinet, then the last two years on the road servicing them. R12, capillary systems, Penn low-pressure controls, Muller Pcquay evaps with Kelvinator condensing units, bulletproof. lol
AAAAAHHHHHHHHHHH HELL!!!!!!! I HAVE MISSED THE OPPORTUNITY TO BE YOUR TECHNICIAN!!!!!!!! 😭 😭 😭 😭 😭 😭 😭 😭 😭
Dude, I just now am really understanding how these f-ing things work!
Thanks Chris!
Yeah just the low pressure control is a great way n very simple. Kinda. You go off pressure not temperature really. Have to watch though because they can be intermittent
Very, very good video…..thanks
Hi there I've just finished installing a new lp/hp switch a danfoss but after setting it up corresponding cut in and diff 17 pressure in psi on a walk in freezer on 404a at -18 to -20 the compressor keeps short cycling is it because of the ambient temp (which was about 4 degrees Celsius) or was my settings not right
When you adjust the pressure according to temperature. Where do you measure the temperature? At coil or box temperature?
Jason
I remember doing this and people kept opening the door while i was trying to let cycle. Frustrated. I learned as long as everything else is properly working you can just set to cut out at 20 and cut in at 39.if charge is proper it shoud never ice up .it is the best way as long as everything else is good
Chris I ran across this exact same setup the other day and was a bit unsure how to fine tune the pressure control then I found this video you posted. It helped me so much. Got the unit running well and the customer is happy. Thank you so much for posting this video, you are an excellent technician and an excellent teacher. You also have been a great help to me on Lennox rooftop units. Love your channel and keep up the great work you do.
Please share about air blast freezer as well. Thank you.
Thank you for sharing ..it really helps
Thank you so much for all this great information,
Hey mate what Fieldpiece app/fool are you using? That looks great – I’ve changed a solid state LP to a manual Ranco LP and I’ve got no idea what I’m doing as the unit has 2x solenoids which Control two cabinets on the one condensing unit
I want it to cut out at 2 degrees Celsius in the box 404a) and back in at 5 degrees I’ve set the cut in at 300kpa and differential at 150kpa so cut out is 150 diff (20psi) it’s cutting the IR33 controller compressor symbol off and the temp rises right up to 10 degrees without cutting the comp out – I’m assuming the solenoids close, lowering the gas pressure and eventually cutting out but hell!, it’s taking forever to cut out 😂 I’m just hoping for the best as I’ve already spent 3.5hrs on site
Friendly Question. Why would you need to wait for the box to come down to temp, 34 degrees, in order to note the pressure and make adjustments. Why would you not just use your pt chart from the beginning for both your cut in and out temp?
wow… I liked this a lot.
You are the man, here is a big question
Can you please make a video adjusting these low and high pressure controls with nitrogen down at the van instead of while its installed on the unit ?
If this is not possible let me know.
Thank you.
The reason they run liquid line and suction line together is to make sure no liquid enters into the compressor.
I control about 90% of our refrigeration with pressure controls only. I've been doing it this way for about 20 years now. I have much better temp contr with out freeze up issues. Are you in Orleans ?
Only a pressure control ?
Hey can you film some ice machine service calls I’ve always done residential heating and cooling and want to start doing some refrigeration stuff and need to learn the controls and so on thanks good video
Lol I'm working on the exact same system. I set the switch to cut out at 45 and cut in at 65. Its been cooling good I just wanted to make sure its been cycling off for enough time. Thanks for the video!!
I would like to make the point that 39 degrees cut in is a little high. I am dealing with health inspectors that are looking for below 40 degrees internal product temperature. If they catch it during an off cycle, I'm worried that they'll flag the equipment as not operating properly. I ended up setting the cut in for 33 degrees.
I have been watching your vids and I am interested in working in the same field with some one who really loves what he do. I have a universal tech.license and worked with comercial A/C for a while but got my own business which is have a lot with industrial refrigeration applications mostly on dry clean machines. If you need someone with a little Experiance you can e-mail me or just responde to me here thank you. Are you in Nepean ?
Is this not the norm anymore? I've never seen one with digital controls.
Thank you doing a video for low pressure control. Excellent video and explained how it works in real life.
I’d think you should be a teacher at a college or a teacher at a technical school Are you in Ottawa ?
You explain things very well. Detailed and precise. Thank you!
How come the TD was so high for a TXV. It was around 23°F I heard you say. Would you prefer to see 15°F TD for a cooler? Service area Kanata??
Old school, low temp control for a stat I dig it Service area Nepean??
What we think about all this ???? We think that you’re really good person and we learn allot from your teaching. Thank you very much God Bless you always
Hello Chris. Was the refrigerant charge ok and do like liquid line sight glasses as a quick reference. I worked for a company awhile back and installed remote condensers for walk ins. My boss never checked superheat but just charged the system till there was no gas bubbles on the liquid line. What’s your thoughts on that ??
You do a good job….👌👌👌👌👍👍👍👍
You are the best!!!!@@!👏👏👏👏👏👏 Are you in Barrhaven ?
Hey great video! What state do you work in?
Not sure if I’m thinking about this right, will this cycle the compressor or the condenser fan? Is this wired same as a relay/contractor, in series on the hot leg? Not sure if I’m mixing this up with a low ambient control. Thanks
Had a cold pack walk-in freezer running below thermostat set point way below to -27 and it’s set for 0. Started troubleshooting and it shut off cycled several times and it worked properly. Any ideas 💡 what would cause this
Would be easier to use a 1609-101 all range temp control and drill a hole for the bulb to get in the box to control temp and not the pressure control
Very good video I Learned more about those low controls ..Thanks for sharing Your skills
Nice video.
One additional note:
Set the cut in pressure to match the refrigerant's saturation pressure at the desired cut in temperature.
Rough set the cut out temperature at the saturation pressure matching 10° colder than your desired cut out temperature and you should be fairly close. A few cycles and you should be dead on your marks.
The 10 degree difference allows for an evaporator coil on a running circuit to reach about the air temp you are looking for as the split between the coil temp and the air temp on a mid temp box is around 10°.
Hope this is helpful.