Just replaced the engine in daughter in laws 2001 3.4 Aztec.
Radiator fans running when A/C on and gauge reads normal.
Shut the air off and it runs hot,gauge very close to red line before fans run.
Why do the fans come on so late and only run a short time?
What can I do to make the fans run sooner?

A few things. The fans coming on with AC uses a differnt set of relays
to turn them on. You could have a bad fan relay, bad tempature sensor
or a problem in the wiring for the sensor.

Since the fans come on with the AC, that rules out a bad fan motor. So
start backing up through the system. Recommend not running the motor
hot to the red line or you'll harm that new motor.

If you had a shop install the motor, take it back.

Nice to hear someone like's their Aztec enough to remotor. The later
production ones without the clading look sharp. But, as in recent
history with the Fairo, Bonnievile and the Aztec and now the departed
GTO, Pontiac gets it right when the plug gets pulled.

Good luck, post back when you get this fixed.

A few things. The fans coming on with AC uses a differnt set of relays
to turn them on. You could have a bad fan relay, bad tempature sensor
or a problem in the wiring for the sensor.

Since the fans come on with the AC, that rules out a bad fan motor. So
start backing up through the system. Recommend not running the motor
hot to the red line or you'll harm that new motor.

If you had a shop install the motor, take it back.

Nice to hear someone like's their Aztec enough to remotor. The later
production ones without the clading look sharp. But, as in recent
history with the Fairo, Bonnievile and the Aztec and now the departed
GTO, Pontiac gets it right when the plug gets pulled.

Good luck, post back when you get this fixed.

A few things. The fans coming on with AC uses a differnt set of relays
to turn them on. You could have a bad fan relay, bad tempature sensor
or a problem in the wiring for the sensor.

Since the fans come on with the AC, that rules out a bad fan motor. So
start backing up through the system. Recommend not running the motor
hot to the red line or you'll harm that new motor.

If you had a shop install the motor, take it back.

Nice to hear someone like's their Aztec enough to remotor. The later
production ones without the clading look sharp. But, as in recent
history with the Fairo, Bonnievile and the Aztec and now the departed
GTO, Pontiac gets it right when the plug gets pulled.

Good luck, post back when you get this fixed.