reefer unit question...possible issue

We hauling a 2006 carrier reefer unit and the temp is set to 36 degrees, however the reaper is having a hard time getting it down to that degree. We have been defrosting it manually as the trip has been going, and it is slowly creeping down but we're not sure why it's not getting down to that temp. Do you know what could be causing this problem?

Help

 

If you get a high coolant temp alarm check your coolant bottle. Carrier has been through a few revisions of these. They will crack at the seam around the neck area or you could have a loose clamp up there. Best thing to do if there's no coolant in the bottle is to pressure test it real quick. This will reveal exactly where the leak is. Also while you're up there check the fan clutch by rocking the fan- the bearings wear out and they can seize up and snap the idler to fan belt which will cause a unit to run in defrost because there's nothing there to run air across the condenser. If you hear a knocking noise but can't see or pinpoint from the ground where it's coming from chances are it's the fan clutch going out. Even though this thread is about 4 years old I hope this can help someone. Not making this stuff up I work on reefers as well as a former trailer mechanic.

 

A few things to check-
1. Scroll through the micro and check your suction pressure. At startup when your box temperature is about ambient it should read around 40psi which is good. If it only reads 25 or something around that area, you have a low charge and possible leak somewhere. As your box temp pulls down close to set temp the suction pressure decreases.
2.- open the left door (or top left black cover if Ultima series) look at the receiver tank glasses while unit is in high speed. You will see 2 glasses with a red ball in each that should be floating. They should be about centered while floating if there is a proper charge. If the balls are not floating at all you need a charge and possible leak repair. Refrigerant oil is clear and can be mistaken for water or condensation so if you look around the compressor, suction and discharge valves and vibrasorbers physically wipe it with your finger to check if oil or water. Also smell it if you find an oily residue. Refrigerant oil has a distinct smell because of the refrigerant that is mixed in the oil.

 

I forgot to mention while in the micro scroll through and view your temperature differential or "Delta T" 10 is acceptable but not great. Anywhere from 15 up is a good td.

 

First, determine what you're hauling and if it was loaded "hot"...if so ,your unit Will struggle for a while.... maybe open your vent door (depending on the product)....but to see if your reefer is working properly ,go to the discharge air screen.....it may be blowing the right temperature but the product is still hot or warm ,so your return temp sensor is still reading high.....So again,.. your reefer is probably working correctly.......What product did you load ,....was is precooled before they loaded it (produce,onions etc).....Start there first before fooling around with something being wrong with your reefer unit.

 

I set my refer unit to 37 degrees....box temp stays at 45...wont cool down...text me some info..569-561-4079

 

I don't know. Reefers are designed to maintain temperature. But never to cool cargo down. It simply does not have the moxie to do it.

If you are in continuous at 37 set, and your temp starts to rise towards 50... you have a problem.

 

It set on 37 continuous run...temp is slowly going down...went from 45.3 to 44.5 in over an hr....there is no service places open on weekends

 

Carrier units in start/stop mode will sometimes refuse to cool to their set temp if the battery is low, or the alternator is having issues charging.

The reason for that is that the unit may not be able to crank again, if it shuts down.

The unit may not display any customer-viewable alarm code.

Check belts. Test battery. Test alternator.

 

Have you checked the refrigerant level? There should be a floating ball type sight glass for refrigerant level.

Also, look for ice on the line leading from the compressor to the heat exchanger. Ice can and sometimes should form in the heat exchanger, but not on the lines leading to it.

If the problem is low refrigerant, you might try to add refrigerant, or see if a truck shop will add some for you. Not much difference between truck AC and reefer coolers, other than size and power. It's the same technology, and will have the same type of fill connection, most likely.

 

How do I check the level...