Problem with return temp sensor wiring

[forestcat]

Hi guys! I have a 53 foot trailer with Thermoking SB-200 unit which is controlled by Thermoguard mP-VI microprocessor. Recently I notice that the temperature would sometimes jump as much as 4 degrees Farenhait for no reason. Once I got a code 13. I noticed when I knock on a control panel with my hand the temperature reading would change, so I suspect the wiring is loose or something. Would you please tell me which wire I'm after. Also if anyone have manual TK-50566 for this microprocessor it would help a lot. Regards from USA, Konstantin

[Robert Hilton]

If it,s the return air sensor then cables RTP & RTN are what you're looking for.

[forestcat]

Could you explain please what does RTP & RTN mean?

[Robert Hilton]

The identification on the wire.
RTP=return air positive wire
RTN=return air negative wire

[forestcat]

thank you for your help! unfortunately I didn't find it. there are tons of wires and I think it is very difficult without manual to find it.

[Robert Hilton]

They run to the controller. If you open up the electrical box you'll find them in one of the plugs fitted into the rear of the controller.

[indycar89]

They should be located in the J3 sensor harness connector, probably pins 1 and 2.

[forestcat]

thanks! I think it will help me a lot!

[reeferj]

and most time it is loose pins, try to replace both pins and see......

[tony2009]

G'day; they're normally a short 2-wire (one brown, one blue)harness with a grade number on the sensor bulb, will be something like 4B.
The same sensor does both applications for discharge and return air; the number is required for calibrating the sensor to the controller.

[Robert Hilton]

Actually the grading will be a number with L,H or nothing meaning low, high or nominal.

[gravy258]

just open the control panel, unplug the two big lower plugs that go the micro, clean them with electrical parts cleaner/brake cleaner, and the female ends on the actual micro, then apply a quality electrical grease to the male ends. Plug em back in, job done.
This is a very common fault, and a very easy fix.

[mjreefer]

i have recently had a simular problem with a TGVI, normaly it is dry joints on processor pins as mentioned above i normally tin the pins with solder to make good fit into sockets and grease, the problem could also be chaffed wire touching earth now and again or internal bad connection inside processor,