Carrier 7500 X4 Heat Mode Question

Any reefer mechanics here? I have a Carrier 7500 X4. Load requires 55 F set point. Outside temperature has been around -5 to +5 F all day. Product is stable as it’s been loaded for 48 hours now and was warehoused and loaded at 55-60

Just seems the unit is really struggling trying to maintain. I was on cycle. Now parked for the night (forecast low of 0 F) I switched to continuous to see how it would react. It’s still bouncing around between heat and cool and high and low speed and I’m not sure which mode is more annoying.

Are there limits to what it can do with a set point of 55 and with temps in the 0F or colder outside? How should the unit behave differently between the 2 modes? Bills do not require continuous mode but I’m wondering what would be the easiest on the system long term in these really cold temps?m

It did fine in cycle the first day where temps were around 30-33 F

I assume they operate similar to a home heat pump system? Don’t heat pumps have limits to what you can expect from them?

I’m glad it’s not forecast to get any colder than presently until it unloads.

 

Turns out there must have been some sort of issue with the unit. It finally stopped heating, shut off, I called and they told me to put it in the heated shop. It immediately warmed back up. Waiting on one of our mechanics to come out and make a determination what might have happened.

 

Something is wrong because it shut down at 45 degrees with a heat system failure (had been running continuous for at least 3 hours). Turned it off/on and it came back up and running but the box temp was still falling and last I checked before backing into heated shop, it was 40 and still falling. So the problem wasn’t about the coolant temp. But as soon as it went inside a warm area, it instantly began raising the box temperature.

 

There is a temperature recorder in this load (single product candy, kind of like mini Reese’s PB cups with a darker chocolate).

Maybe the temp was below 50 (55 set point) for 2-3 hours? Maybe it recorded 40 degrees for 20-30 minutes?

Going to be interesting to see if Trader Joe’s rejects the load.

 

I agree it won’t ruin the product. I think it would take a light freeze to discolor them and make a noticeable change, but quality control is quality control. We’re talking about 30 pallets so there is a lot of product “on the outside”

They’re kinda like quarter sized ‘Reese’s Peanut Butter Cups’ in a “muffin” paper cup, then wrapped with a decorative Trader Joe’s foil. I know because I was given about 4 lbs of them (unwrapped seconds) as a driver appreciation gift.

 

Our Carrier rep in Fargo has confirmed there is a programming issue with the last update on heat loads in very cold ambient temps. They’re going to come out and put older software on them to get us by for now. We have another in Fargo (sister load to mine) and one in Ohio having the same issues.