This repair and service manual covers automatic transmission and transaxle theory, maintenance, diagnosis and repair.
Book Excerpt: Chilton's Automatic Transmission Diagnosis and Repair: Auto Transmissions and Transaxles
FLUID COOLER FLOW TESTING: DESCRIPTION
There are two basic tests used to determine if the ATF cooler is functioning properly.
SWITCHES AND RELAYS
A flow test and a pressure test are used to provide information about cooler and transmission/ transaxle operation.
If the ATF cooler becomes clogged for any reason, the result will be reduced flow and less pressure in the lubrication circuit of the transmission.
The reduced flow will also raise the operating temperature of the fluid and greatly decrease the life of the fluid and the transmission/transaxle.
With the development of four speed transmissions/transaxles, good fluid flow is even more critical due to the reduced speed of the fluid pump.
Modern vehicles usually cruise at about 1500-1800 rpm at highway speeds. The speed of the pump is in direct relation to the speed of the engine.
In other words, the speed of the fluid pump in today's vehicles is considerably slower than the speed of the pumps in vehicles a decade ago.
Some electrical components which require a large amount of current to operate also have a relay in their circuit.
Since these circuits carry a large amount of current (amperage or amps), the thickness of the wire in the circuit (wire gauge) is also greater.
If this large wire were connected from the load to the control switch on the dash, the switch would have to carry the high amperage load and the dash would be twice as large to accommodate wiring harnesses as thick as your wrist.
To prevent these problems, a relay is used. The large wires in the circuit are connected from the battery to one side of the relay and from the opposite side of the relay to the load.
The relay is normally open, preventing current from passing through the circuit. An additional, smaller wire is connected from the relay to the control switch for the circuit.
When the control switch is turned on, it grounds the smaller wire to the relay and completes its circuit.
The main switch inside the relay closes, sending power to the component without routing the main power through the inside of the vehicle.
Some common circuits which may use relays are the horn, headlights, starter and rear window defogger systems.
Subject: Automatic Transmission diagnosis and repair. ISBN-10: 0801989442 | ISBN-13: 9780801989445 | Chilton 8944