Abbreviations such as GCR, Generator Control Relay.
UV, Under Voltage.
OV, Over Voltage.
These are depictions to simplify the circuit. There doesn't have to be a physical relay. It could be an actual transistor that's doing the job. They could be logic circuits also.
The square opening at back of the operating blower is used for discharged air.
When a blower is running, its own flapper is being pushed back to let the air escape.
The non-running blower will have its flap pulled "in" because of the suction through the manifold.
We recently had a aircraft with a #1 blower failure (the #1 is the primary and is powered up first).
The blower failed which caused the system to use the #2.
The flapper on the back of the #1 was missing.
As the #2 was blowing, air entered the back of the #1 blower into the manifold.
No air was drawn through the detectors and the pressure switch was not being activated.
The system threw a EICAS message of "Cargo Det Air" because all smoke detection in that bay was inoperative.
Crappy image, but it shows the location of missing flap for the #1 blower.
Ref:
rotate.aero/forum/test-equipment/224-fuel-quantity-test
You need a PSD-60 or equivalent fuel quantity test unit. You need the appropriate break-out test cable. You need the test adapter to check individual probes at the bussing plug.
NEVER USE A CONVENTIONAL MEGGER FOR ANYTHING INSIDE THE TANK!!!