trans air ec3.0 electronic climate control system

7/30/2019 Trans Air EC3.0 Electronic Climate Control System

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Trans/Air EC3.0 Electronic Climate Control System 1

1. DESCRIPTION

This publication consists of information provided by Trans/Air, and is provided “as is”without warranty of anykind, either expressed or implied. Navistar, Inc. assumes no responsibility for errors or omissions in this

publication or other documents that are referenced by or linked to this publication. In no event shall Navistar,Inc. be liable for any damages whatsoever (including special, incidental, direct or indirect, or consequential

damages) arising out of or in connection with this publication and the use of the information contained herein.



Figure 2 Relay Board Layout

Table 1 Relay Configuration

RELAY FUNCTION Currant rating

COMPR. Compressor clutch relay 10 amp



10 Ground

11 Evaporator power return

12 Evaporator power input

Table 4 LED ListINDICATOR FUNCTION

D25 Comp. Illuminates when compressor relay is engaged.

D26 Cond. Illuminates when condenser is engaged

D27 Tie-in comp. Illuminates when tie-in compressor relay is engaged

D28 Tie-in cond. Illuminates when tie-in condenser is engaged

D29 Heat Illuminates when heat relay is engaged

D30 Com. Illuminates and flickers when board is powered up

D31 Evap. Illuminates when evaporator is on

System Operation

Basic system operations are covered by the instruction manual (701465).

Thermostat Control Logic:

Temperature sensing

EC3.0 system has two thermistor type temperature sensors: cabin (internal) air temperature

sensor and ambient (external) air temperature sensor. The cabin air temperature sensor ismounted in front of the main evaporator return air filter and the external temperature is

mounted externally but the location varies depending on vehicle models.

The electric resistance of the temperature sensor changes with the temperature. The sensingi i h l b d d h i d i di Th



When the external temperature is below 34ºF, the compressor clutch and condenser will belocked out to prevent condenser motor damages. If the external temperature sensor is

damaged, it may feed false low temperature signal to the board and cause the system

malfunction.

Fan Speed Control

EC3.0 system has two speed control modes. Auto fan speed control and manual fan speed

control. In manual fan speed control, there are three settings High, Medium and Low. In

auto fan speed control mode, evaporator blower speed is controlled based on the temperaturedifferential between Tin and Tset. The greater the temperature differential is the higher the

blower speed is. The evaporator blower is controlled by a series of transistors instead of

relays. By changing the duty ratio of the transistors, the supply voltage to the blower can be

varied. As the blower speed is proportional to the input voltage, the blower speed can becontrolled by duty ratio. The fan speed control setting are listed in Table 6.

Table 6 Fan speed control settings

Mode Setting Duty Ratio

| Tin-Tset | ≤ 2ºF 60%

2Fº<| Tin-Tset | < 4ºF 70%

4Fº≤| Tin-Tset | < 6ºF 80%

6Fº≤| Tin-Tset | < 8ºF 90%

Auto

8Fº≤| Tin-Tset | 100%

High 100%

Mediu, 80%

Manual

Low 60%



the safety wire it is connected to will have the same voltage as the common wire. If a safetyswitch is open the respective safety wire will be open (floating). Therefore the EC3 system

can identify which safety switch is open. In the event of safety fault(s), the compressor

clutch and condenser fan will be turned off and remained off until the fault code is cleared.

The evaporator blower speed will be changed to high speed and the thermostat will displayspecific fault code to alert the operator.

Beside safety switches, EC3.0 also monitors two other electrical faults: low clutch voltage

and blown fuse. The EC3.0 system senses the voltage on terminal 8 (clutch power inputterminal). If the voltage on terminal drops below 11.9 vdc, EC3.0 system will turn off

condenser output and compressor clutch output and display “Lu” low voltage fault code on

the thermostat display. EC3.0 system also sense the status of fuses including 3 on-boardfuses (ATC blade type fuses), and external fuses. The system actions under these two fault

modes are also listed in Table 8.

Table 8 Faulty codes list

Fault Type Code Description System Actions

HP High pressure switch open

LP Low pressure switch open

Fr Freezstat open (if equipped)

Safety

Lu Two or more safety switches open

Display fault codeClutch output OFF

Condenser output OFF

Evap. speed High

bF Blown fuse or

No voltage on terminal 6, 8 or 12.

Electrical

Lu Low compressor clutch voltage

Display fault code

Clutch output OFF

Condenser output OFFEvap. speed High

Note: “Lu” code has two possible causes.



Slave board configuration

In some large systems where the electrical load exceeds the current capability of a single

board, a slave board can be used. A typical wiring diagram is 5031xxxx. In a slave system,the switches are connected to the master board and the slave board is connected to the master

board through a harness 701442. The slave board mimics the actions of the master board.The slave board normally is used to drive the additional evaporators and condensers.

Trouble shooting

Use Table 8 to identify the problem if there is a fault code. Other common problems are

listed in Table 9. Refer to previous sections for detailed action procedures.

Table 9 Trouble Shooting

Symptom Probable causes Action

Switch does not turn on No power Check COM LEDCheck terminal 5 for +12vdc

and 10 for ground

Faulty communication cable Replace cable

Faulty switch Replace switch

Faulty board Replace board

Clutch does not engage Tset> Tin Adjust set pointFaulty external temperaturesensor

Replace temp. sensor or sensor cable

Bad connection Check LED on board andvoltage on terminal 1

Faulty board Replace board

trans air ec3.0 electronic climate control system

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