Thermo King SBIII Alarm Code 29???

[ppodsiadlo]

Hi All,

I have a Thermo King SBIII Max unit, year 1995, 18,000 hours. When I set a target temperature to lets say 26 F, the cooling kicks in for about 2 minutes and then switches to defrost for about 1 minute. It doesn't cool down and just switches between the two. After w fe minutes I am getting alarm code 29. I had this situation a year ago, when it was raining quite a bit. After about a week the problem went away and worked fine until now. Please help.

Also, does anyone have a service manual for the unit. I also want to check the defrost sensors, but I am not sure where they are? How many of them are there?

Thanks,
Paul

[absolute-zero]

Hi All,

I have a Thermo King SBIII Max unit, year 1995, 18,000 hours. When I set a target temperature to lets say 26 F, the cooling kicks in for about 2 minutes and then switches to defrost for about 1 minute. It doesn't cool down and just switches between the two. After w fe minutes I am getting alarm code 29. I had this situation a year ago, when it was raining quite a bit. After about a week the problem went away and worked fine until now. Please help.

Also, does anyone have a service manual for the unit. I also want to check the defrost sensors, but I am not sure where they are? How many of them are there?

Thanks,
Paul

Based on the description you have given, I would guess that it is the evaporater differential pressure switch. You say it runs a couple minutes, perhaps soon as the unit calls for high speed operation, the diffential on both sides of the evap change.

Couple things I would check..

Basics.....

• Make sure the evaporater coil fins are clean. no dirt or plastic debris.
• Verify that the return air and discharge stream is not obstructed.
• Verify the air switch wiring, and hoses are connected and in place from the switch all the way to the evap section.
• Finally using a magnehelic gauge test the air switch setting. it should be around 1.0 in

Good luck

A-Z