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T-stat bulbs in coils function just as a refer unit using a Ranco low pressure control switch for temperature control as you might see on smaller/older reach-in's. I've experimented with either/or on 10' pizza make tables and the large retarders and compared watching suction temps. It's kind of neat and a good study in refrigeration theory.

Originally Posted by MicahWes

I have seen maybe 5 (standard TXV style) walk-ins with sensing elements in the coil in maybe nearly 1000 walk-ins. WHY are sensing elements in the coil more reliable with better control? Why don't all the WIC manufacturers use this system of control if it is hands down superior? Cost certainly isn't the concern.

In 90% of WICs it's not nessisary nor is a defrost timer. But 10% of them will be let's say special. Prone to frosting up for non refrigeration system issues. The bulb in coil is a more effective way to control this frosting because it will shut comp off at the onset and start comp as soon as coil reaches cut in temp,too warm for frost to exist. Where as a timer is all about timed cycles. Prop door open 10 minuts after a defrost cycle on a humid day and a service call and manual defrost are likely.

I have seen maybe 5 (standard TXV style) walk-ins with sensing elements in the coil in maybe nearly 1000 walk-ins. WHY are sensing elements in the coil more reliable with better control? Why don't all the WIC manufacturers use this system of control if it is hands down superior? Cost certainly isn't the concern.

Originally Posted by J_Bridge

Stick a tstat of a walk in cooler in the coil? What? You should never do that! Return air is where the bulb should be at, t-stat set to cut out at 32 degres in ice water(calibrate). The numbers don't always match up. Super heat at 10-12 degrees with 4 x 30min defrost. The lowee cutout will ensure proper food temp coming out of the w/i/c. These defrost are needed in the south, with the warner air and high humidity situations. This is an off cycle defrost. You should be good, but if they call back with a warm box. Take the timer and be done with the call.

Never is a big word. Personally I prefer bulb in coil over timer on WIC for all the reasons 2SAC said. More reliable better control. Not saying timer is wrong at all but in my 23 years in this field I have found it less effective then bulb in coil.

[QUOTE=Navy06;14937321 you will always need a defrost on any system.[/QUOTE]

5 days not going into defrost will not hurt it but it should get the new clock. you will always need a defrost on any system.

I am so used to having high cut ins and outs (being where I'm at for back up) that I forgot there are people in cold climates. 2sac corrected me rightly.

Cut ins he's exactly right. For cut out, I set a med temp box no lower than I have to. Maybe 10* coil if possible. If the clock fails and/or the tstat/sol. is stuck , the coil ices and loses airflow, the suction will drop quickly.
If the cut out is set real low , there will be a long deice job soon. I set cut in/out as high as possible to prevent Ice block on coil.


What I am saying is, if the cut out is set real low...(3-5-10# r22 example), the evap is getting unnecessarily too cold.
If the system needs to run at the 5* evap range (for a medium temp box) there are design and sizing issues..more than likely the system is a problem child already. You gotta do what you gotta do to make the box run, but I like high as possible settings..That's all I'm saying.

Originally Posted by Snapperhead

I set most of my coolers around 5 psi cut out , and 40 cut in .....

Knucklehead maybe , snapperhead for sure

Depends on ambient during the winter. CI is set to the pressure equivilant of the coldest ambient temp it will see. Years ago ICS shipped a bunch of coolers and freezers to YUM Brands resturants in Chicago that were being installed on new construction and remodels. They had encapsulated LPC's with a 40psi CI @R22 We kept busy during the wintertime.

I set most of my coolers around 5 psi cut out , and 40 cut in .....

Knucklehead maybe , snapperhead for sure

Originally Posted by MicahWes

Say what now???

Guess he is saying when it pumps down all the refrigerant is sucked out and the coil no longer has a cooling effect.

I would say 5% of the walk-in coolers around here have off-cycle defrost clocks. I put one in earlier this year with a problem account. They are generally not necessary.

Originally Posted by NedFlanders

Most knuckleheads bury a Med Temp system LP control to cut out at 3-5 #. Every time it pumps down, you drag the coil temp into the toilet. There is no need for that.

Say what now???

out of all the coolers I service maybe 1% have a defrost clock....... you usually don't require one.....

Originally Posted by 2sac

I believe a manufacturer like ICS for example who drops their boxes complete, minus plumbing and power, off a trailer won't put a bulb in a coil for a number of reasons. The first on being someones going to mess with it. Improper startup procedures, lack of knowledgeable techs, possible breakage during shipping to name a few. If I set my CI between 38-40 and set my CO appropiately it will not freeze up. Fast food restaurants are notorious for proping doors open. With the bulb in the coil as soon as the coil temp reaches the CO setpoint the compressor shuts down and will not come back on until the coil temp reaches the CI setpoint not allowing the coil to freeze. With a door propped open and the bulb in the return air the compressor will run forever.

Neither way is incorrect. There is just more than one way to skin a cat.

One of our guys called ICS with a question, and he said they don't actually make the equipment, they just put their name on it. Any idea who actually makes the stuff?

In my world units are undersized Boxes are poorly insulate with leaks,loaded with hot steaming food etc. On Indoor condensing unit temp was frequently controlled by the LP switch. I have placed t'stat bulbin the evaporator coil on outdoor units too allow proper defrost as it mimics the action of the LP switch. If you set the cut in to box cut in and adjust cut out according to appropriate coil temp drop box maintains temp based on coil temp.

Bridge ..... lets take a refrigerator with the bulb hanging in the airflow , and its suddenly packed with warm product and the box temperature shoots up to 60°F. The compressor starts, but it has a long journey before the box temperature drops all of that warm product to 40°F. The coil begins to frost, blocking airflow and heat transfer. Because the frost is insulating the coil from the warm boxes temperature , the evap temp continues to fall eventually forming ice. This Air sensing stat keeps the compressor running because it still senses 60 degree product, adding to the frost problems .... however if the bulb was indeed mounted in the coil fins, the stat would shut down the compressor when the evap dropped to the cutout temp of 25. Then while the compressor was off the Fans would be steadily running circulating the warm box temp air over the evap melting the frost ,and when the coil defrosts to the point of ultimately raising the coil temp to 40 deg cut in , the compressor comes back on. This cycle continues back and fourth until both product and box are at same temp.

Like 2sac said , both work , but the air sensing one needs a time clock which is alot more wiring and more crap to go bad.

I believe a manufacturer like ICS for example who drops their boxes complete, minus plumbing and power, off a trailer won't put a bulb in a coil for a number of reasons. The first on being someones going to mess with it. Improper startup procedures, lack of knowledgeable techs, possible breakage during shipping to name a few. If I set my CI between 38-40 and set my CO appropiately it will not freeze up. Fast food restaurants are notorious for proping doors open. With the bulb in the coil as soon as the coil temp reaches the CO setpoint the compressor shuts down and will not come back on until the coil temp reaches the CI setpoint not allowing the coil to freeze. With a door propped open and the bulb in the return air the compressor will run forever.

Neither way is incorrect. There is just more than one way to skin a cat.

I have been doing this for over 13 years and my company for over 35 years and we have never had a tstat in the coil on a WIC. But let me clarify what I am calling off cycle defrost. We always recomend and install pump down systems and install defrost time clocks. As I stated earlier the defrost is 4 x 30min, sometimes we might go to 6 x 30min if it is a high traffic box or they are putting hot product in it. We set and mark the tstat to cut out near 32 degrees on return air temp. If your super heat is set properly 10-12 degrees, and you can go lower as long as your superheat at the compressor isn't below 20 degreees during the busy time(this ensures that during the low load at night you still have superheat at your compressor). This will prevent the coil from freezing up. This all being said you need to be checking the size of the system and the box size. I always do tis when it is a job site we don't normally service or if we have had multiple issues on the system.
Back to the bulb in the coil, none of the manufactures put their bulbs in their coils on WIC's. Their bulbs are always in the return air, Their is a reason the factories don't put them in the coils.

Originally Posted by 2sac

That may work in California, but it does not work where low ambient temps exist. If the outdoor temp is lower than the space temp, the refrigerant will stay in the receiver unless the receiver is wrapped in heat tape and insulated. This used to be a regular practice with R12

true...good point

Originally Posted by NedFlanders

Low pressure controls save lives....Compressor lives

You can get by in setting the Low Pressure control to a higher cut in temp. If you "cut in" at 38*- 40* (converted coil temp estimated) and "cut out" at 18*- 20* (converted coil temp estimated), you'd be surprised how long and how well it will run like that. The warmer "cut in" will defrost it every time it off cycles. Not to mention , you can mellow out comp cycle starts at the same time. You have to play with the numbers , but it works almost all the time.
The pressure control will run a system (if set up correctly), better than a t-stat most of the time.

Most knuckleheads bury a Med Temp system LP control to cut out at 3-5 #. Every time it pumps down, you drag the coil temp into the toilet. There is no need for that.

That may work in California, but it does not work where low ambient temps exist. If the outdoor temp is lower than the space temp, the refrigerant will stay in the receiver unless the receiver is wrapped in heat tape and insulated. This used to be a regular practice with R12

Originally Posted by NedFlanders

Low pressure controls save lives....Compressor lives

You can get by in setting the Low Pressure control to a higher cut in temp. If you "cut in" at 38*- 40* (converted coil temp estimated) and "cut out" at 18*- 20* (converted coil temp estimated), you'd be surprised how long and how well it will run like that. The warmer "cut in" will defrost it every time it off cycles. Not to mention , you can mellow out comp cycle starts at the same time. You have to play with the numbers , but it works almost all the time.
The pressure control will run a system (if set up correctly), better than a t-stat most of the time.

Most knuckleheads bury a Med Temp system LP control to cut out at 3-5 #. Every time it pumps down, you drag the coil temp into the toilet. There is no need for that.

This would work on a non pumpdown system. Otherwise you'll short cycle the compressor and be in worse shape than a frozen coil. I still have 3 coolers that operate this way and haven't had any trouble with them in the 3 years I've been doing refer work here.