View Full Version : Thermo king sb-310 not cooling right

07-07-2015, 05:01 PM
Hi guys, I think I have a problem with my reefer, but dont know which one. The reefer is loaded with frozen gelato which we have to keep at -20F. Temperature in the box is -5 now.
Discharge air temp is -16.7 F
Temperature differential is -12.2 F
Coil is -9.1 F
Ambient temp is 101 F
I think something wrong with sensors. How could discharge air be cooler than the coil?
Also suction pressure is 10
discharge pressure is 358
ETV position is 800
Where should i start?

07-07-2015, 09:23 PM
coil temperature is normally somewhere between the return and discharge unless the coil is iced up.
A 310 will have redundant return and discharge air temp sensors so if one acts up it will almost always set a code.

Suction pressure is a little low, discharge is a little high.
I'd start by giving the condenser a good wash and checking the ***** level.
Is the ball up in the sight glass on the receiver tank?

08-07-2015, 02:11 PM
thanks , yes the ball is in upper part of a glass. last week i took this unit to dealership because with closed doors empty trailer working whole night pulled temp to 6F and shipper requires -10. outside temp was in 80. thermo king dealership added 4 pounds of *****.
suction pressure today is 13 and discharge 330.

09-07-2015, 12:47 AM
Cleaning the condensor is a must do but only use mild detergent get it running and clean it while it running the colour of the water running off underneath will show you how dirty it is,why did the dealer not clean it? Feel the filter drier when running before you clean it then feel it afterwards basically it should feel less warm than the water you bathe in.

09-07-2015, 12:59 PM
thanks for suggestions. i have 2 older units and will clean them both . do i need a special equipment or just a pressure washer ? the coil is accessible from the rear of a trailer?

10-07-2015, 07:25 PM
thanks for suggestions. i have 2 older units and will clean them both . do i need a special equipment or just a pressure washer ? the coil is accessible from the rear of a trailer?

The condenser is on the outside of the unit, the evap is on the inside. Cleaning the evaporator isn't a bad idea either (depending on what you're hauling) To get at the evap you'll need to remove the bulkhead and the centre panel. To get at the condenser you'll need to open both roadside panels, the lower panel will have thumbscrews from the inside, the upper will have two 7/16" head bolts. Be cautious with a power washer, you can easily bend the fins and make things much worse. A good garden hose will work.
Like Cad says, keep washing till the water coming out the bottom is clean. Could take a bit if it's real bad.

10-07-2015, 08:18 PM
Not liking pressure washer they are dangerous in the wrong hands we have a different climate over here but a garden watering can with a good mixture of washing up liquid and water tipped over the condensor while running the rinsed with a garden hose is sufficient.

11-07-2015, 12:06 AM
Thank you , that even better, would wash them with regular hose. I would do condenser first and see if it helps. We haul everything from frozen ice cream to potatoes from the field. later i would do evaporators. thank for pointing it out, i was confused

11-07-2015, 01:13 PM
theres nothing wrong with your reefer, its running the right head pressure for the ambient and -5F is well in the frozen range (-20c)
I would probe the load when you put it on, most icecream is only frozen to -2f (-18c) minimum.
We used to load icecream in Australia in same ambients at -9f(-22c)
Leave it on continuous run also, its too hot to have it start/stop.

11-07-2015, 02:19 PM
yes, i think so too now, but still before reefer was cooling much better . even empty it took it 7 hours to pull from 80F to -2F ambient temp was 90F. And reefer is thermo king sb-300 it has a big compressor. I would wash condenser coil and maybe evaporator and see if it cools better.

12-07-2015, 01:44 PM
all normal parameters. It would take that long to cool to -2F in that ambient, as it has nothing to cool.

check your door seals etc.. are OK, get someone to shut you inside briefly, you'll see daylight if there's a problem. This can affect high ambient cooling capacity.

Manually defrost the reefer 15 minutes after it has been loaded. This increases optimum cooling capacity.

Make sure the defrost drains are clear, water should run out of bottom of both after the first defrost.

That's about it.

12-07-2015, 02:18 PM
Good to hear! I would definitely inspect for holes etc.