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