Thermo King KDII Issues

[Puff-n0eyebrows]

I have been working on a thermo king KDII MAX for a customer for some time now. Unit has been working great for about 1 year or so. Untill today. He called me and said that it was not operaiting at all and the digital display was totally blank (all controls and switches were turned on). I discovered that the unit was tripping a small circut breaker that is attatched to the lower left control board. This short in the system is very intermittent and only lasts for about 15 seconds or so then "un-shorts" itself for lack of better terms. I cannot find the short because it happens so fast. The only thing that seems to be somewhat consistant is that it seems to only happen when the motor is on low speed, possibly when it is cycling between cool and heating. I have checked the coils on the valves to see if they are shorted and when I check them they aren't. I am leaning towards changing the t-stat because is it is the only other thing that changes when cycling between cooling and heating. Any help or maybe a service manual would be awsome. Thanks everyone! -Kyle

[cebunting]

is it the circuit breaker for the engine protection? (low oil pressure, high engine temp)

[DaButcher]

http://i543.photobucket.com/albums/gg445/DaButcherMudMafia/reefer/Clipboard01-4.jpg
CB1 or CB2 is tripping?

[Puff-n0eyebrows]

is it the circuit breaker for the engine protection? (low oil pressure, high engine temp)
After following every circut (after this breaker) yesturday I never ran across any of the sensors for engine protection like oil pressure ect. Although the engine protection reset switch is in this circut. Speaking of that, I am not fully understanding that reset switch. It appears to be like a bimetal heater or something, I suppose so if there is a small fluctuation in the oil pressure or temp it has a time delay maybe???? That switch never trips. Does anyone have a service manual for this thing. One that might show resistance values for different items. Thanks again. -Kyle

[Puff-n0eyebrows]

Cool a picture. It is the CB2 that is tripping. The one thing I have for surely narrowed down is that I can remove the 2b wire that goes to the fuel relay and the problem is still there. This circut breaker feeds many things as you can see. Also this unit does have the remote on/off switch and status light kit.

[abbsnowman]

3 things cause that breaker to trip. Yes it does use heat via ground through either the oil pressure switch or the hi engine temp switch. The other cause is the hi pressure switch. If tripped, it will not allow power to go to run solenoid. Engine quits and oil pressure switch goes to ground and trips breaker.
My money is on the oil pressure switch because it uses a diapham and if it develops a leak in diaphram, when engine goes into low speed, oil pressure drops and trips breaker. Disconnect oil pr. switch to test. DO NOT RUN TOO LONG IN CASE THERE ACTUALY IS LOW OIL PRESSURE!!!
Hope this helps??
Abbs

[Puff-n0eyebrows]

3 things cause that breaker to trip. Yes it does use heat via ground through either the oil pressure switch or the hi engine temp switch. The other cause is the hi pressure switch. If tripped, it will not allow power to go to run solenoid. Engine quits and oil pressure switch goes to ground and trips breaker.
My money is on the oil pressure switch because it uses a diapham and if it develops a leak in diaphram, when engine goes into low speed, oil pressure drops and trips breaker. Disconnect oil pr. switch to test. DO NOT RUN TOO LONG IN CASE THERE ACTUALY IS LOW OIL PRESSURE!!!
Hope this helps??
Abbs

What should the oil pressure be on high and low speed. Thanks!

[abbsnowman]

I'm way to lazy to look that up but I would not expect less than 20 and 40.
I'm fairly confedent in my original diag. but never possative! lol

[DaButcher]

low oil pressure switch closes at 10 psig plus or minus 3 psig (69 kPa plus or minus 21 kPa)

normal oil pressure is 35-60 psig (241 to 414 kPa

Eliminate the oil pressure switch by removing the wire from it and see if it still trips your circuit breaker while running

[Will]

Shall I assume CB2 is that old 'resister-heater-melt-the-solder-pop-the-button' breaker ?

[abbsnowman]

Shall I assume CB2 is that old 'resister-heater-melt-the-solder-pop-the-button' breaker ?

That would be the one.

[absolute-zero]

This thread has me completely confused. What does the safety reset switch have to do with CB2 popping?

A-Z

[Will]

This thread has me completely confused. What does the safety reset switch have to do with CB2 popping?I was too, that's why I asked the question in post #10. Are they not the same ?

[absolute-zero]

I was too, that's why I asked the question in post #10. Are they not the same ?

No they are not the same. CB2 protects the 2B circuit and remainder subcircuits while the 8D and 20 circuit go to the safety reset switch and open anytime there is ground on the 20 wire via, low oil press switch, low oil level switch, high water temp switch, and high evap temperature switch if applicable.

I like you am confused as to what influence the CB2 has with the safety reset switch and vise versa. I am sure someone will come on and explain or offer some clarification.

A-Z

[abbsnowman]

I think the confusion is cause by me in post #6. I thought he was talking about it it being caused by the op switch etc. I misread what he wrote. Sorry, my fault.

[The Fox]

if you are sure it is cb2 tripping you need to be looking at circuits past the on/off switch. have you had an ammeter in the circuit to check that you do have a short?. the circuit breakers can go soft and trip under normal load. think cb2 is around 20 amps.
one i have seen many times is the damper door shorting on the nimber 29 wire on the defrost solenoid, when the unit goes into defrost the damper closes and shorts on the soleniod terminal and trips the circuit breaker. good hunting

[absolute-zero]

if you are sure it is cb2 tripping you need to be looking at circuits past the on/off switch. have you had an ammeter in the circuit to check that you do have a short?. the circuit breakers can go soft and trip under normal load. think cb2 is around 20 amps.
one i have seen many times is the damper door shorting on the nimber 29 wire on the defrost solenoid, when the unit goes into defrost the damper closes and shorts on the soleniod terminal and trips the circuit breaker. good hunting

The other one I have seen that causes the CB2 to pop is an internally shorted intergral fuel solenoid, or a defective pull-in timer. But based on the symptoms that were supplied I would be inclined to agree with Fox that there is an issue with the defrost damper circuit.