Tuesday, July 19, 2011

cooling fan relay location for Crown Vic P71 Police vehicle?

Here's the wiring diagram and the relay locations. The high speed relay is in another smaller box between the main engine fuse box and the heater core. The low relay is in the main box behind the battery. The fan should come on high speed when the air conditioning compressor is running. The low, not until the engine gets over half way. Maxi fuse #13 is for the high speed relay and the circuit breaker #17 is for the low fan relay.

Same image picture again:---
If it doesn't run and the A/C is on and cooling. check for power at the orange/light blue wire. If it has power there. the fan motor is bad unless the black wire isn't grounded. We have replaced those fans a few times.

If the A/C wasn't kicking in, then that's a different situation. When the pressure switch for the A/C senses pressure, it turns the fan on to high. The engine temp sensor would turn it on to low when the temp goes a little above ½ way up the gauge.

The PCM controls the clutch but the 2 pressure switches have to be closed. With the A/C on and the engine running, power should gothrough both switches to the PCM. Check the black/yellow wire at the high pressure switch. If no power there, go to the low pressure switch and see if there's power on both sides.
Here's the circuit for the A/C clutch.

fan will not run at all, nor will ac compressor cycle in and out,

yes, if you let it idle, temp gauge will go into red zone. this is without ac on. fan will not run at all.

Pull that #3 relay out and jump across the sockets where pins # 30 and the upper #87 go. The fan should run even with the key off. If it doesn't. you need a new fan as long as the black wire to the fan is a good ground.

the second relay box is directly beside the first one right behind battery. it has two relays.
That relay is only for the high speed when the A/C is on. The other relay in the box by the battery is for overheating. Something isn't triggering them. You can also switch relays with other positions for testing. All of the relays should be the same.

There's a larger fuse box right behind the battery and it's between the battery and the box with the 2 relays you mentioned. Relay #3 is for the low fan. The PCM controls the relays. If the A/C isn't coming on, it won't trigger the high fan relay. The low fan relay is a different circuit that is controlled by engine temp. There could be a problem with that part and without A/C, the high fan won't come on.

Now read this question and its answer carefully:---
so relay 3 in the big box is for low speed cooling fan based on engine temp, and if this relay is bad, the fan wont run at all even on high speed with the ac on. and as you mentioned, what about circuit breaker 17? how can i test this relay, and the circuit breaker? so basically the high speed wont run if the low speed relay is bad because the low speed is based on engine temp which is the primary circuit for kicking on the fan, and it only shifts to high speed when the ac kicks in for extra cooling?

They're two different circuits. If the A/C is inop. the high circuit won't run. That part may be okay and just because the A/C isn't working it's inop. It's like if the engine temp wasn't working for awhile and the fan worked with the A/C. Then when the A/C quit, the high circuit wouldn't work and thtat might be when the low cicuit problem was noticed. If you get the A/C working, maybe the fan will work on the high circuit.

questions REPLY;--
pulled #3 relay and replaced it, and while i was at it, i replaced the high speed relay. started engine and let it warm up. at about halfway up on temp guage, fan kicked in perfectly, ran just a few minutes, then kicked out. it kicks in and out just great.-------