Start/Stop vs Continuous

Depends on the load. Some loads like candy can be destroyed if frozen. So yes, I suggest you stay as close as possible to the setting dictated on the bills.

 

Regarding deep frozen product. I'll disagree on bills state 0 so it's not okay to run at -10. Lots of time the freezer is set at 0 so they request 0 in transit. But the thing is 0 would be the highest temperature that would be allowed. Setting a start/stop at 0 is going to produce occasional temps of +5 which might trigger a load audit.

0 and -10 are acceptable deep frozen temps. Colder (on deep freeze loads) always gives you added time insurance in the event of a unit failure. However there is a point where the law of diminishing returns kicks in and it's around-10f. Ice cream is another matter. Ice cream should never be hauled in non ice cream rated trailers.

 

Depending on the product, the difference between 0 & -10 may cause crystallization/separation.

 

I agree about the ice cream. However a lot of drivers confuse ambient temp with the actual temp of the load. That temp sensor is attached to the inlet of the reefer and only measures the ambient temp, remember air is always moving around in the trailer when that reefer is running. So it is possible to have a +5 as a reading and have the load still sitting at 0. Because of the nature of thermostats and how they work these ambient temps will drift based on how the thermostat cut in and cut out is set. Even your house AC system works like this. In fact it is almost impossible to maintain a single temp over time.

 

There is a great video produced by Carrier that gets into deep detail on how reefers work. I have seen it. I just can't find it on youtube. I guess it's copyrighted and nobody has took the time to upload it. That video shows how to set reefers and why. I will see if I can locate a MP4 of it and upload it to youtube.

 

Its just not rocket science, set it and forget it. The only thing I did not run continuous was products I was keeping from freezing, everything else goes at what the shipper or customer wants.

 

I am glad this thread got bumped up. I was going to tell a story about a rejected load I had some experience with in Florida. To make a long story short there was only 4 pallets on the truck. I forgot what the bills called for temp setting wise. However the reefer was set to that specific setting called for in the bills. It was hot that afternoon and when I opened the trailer doors there was not much load in the trailer to hold the temp. After several minutes in that hot humid Florida air the ambient air went way up even with the reefer on. My company sent me to TK and they downloaded the data from the reefer memory and once printed you could see how the air in the trailer was cycling as the thermostat cut in cut out operated it. Not sure what the shipper did after that, but those printed pages were faxed to them. I was covered by that readout as was my company.

 

Most all will specify a set point but not many will specify a mode. And furthermore I agree about the fact that "box temp" indicated, and actual stabilized product temp are generally two different things, however there are more than a few places who place a great deal of emphasis on what the "box temp" states at gate arrival. This can be a problem, especially with chilled loads like dairy, that are ran on cycle.

If shipper and boss says cycle is okay on chilled loads, I've still learned to flip it to continuous just prior to gate arrival to make sure the observed temp matches the desired temp.

 

Yes places like Walmart DCs will take temp readings from that gauge and put it on the bills. However some DCs after they start unloading will stick a temp probe in a sample product and measure the temp. I have seen this with my own eyes. I have seen this done with fruit and it has been correctly noted some shippers put tattletales in the loads too. As a driver all you really can do is just follow what the shipper says and keep the fuel tank full. As has been also noted it is not rocket science.