Bad ground?

[tpm64]

Two problems have crept up recently on our 07 F53 20,500 gvwr Georgie Boy Landau.

The first is that the AC compressor has stopped engaging. The dash switch checks out fine. Fan works fine. The Ford relay never engages. I have swapped relays and tested them OK. What I think should be the ground side of the coil on the relay reads 13 volts whether the switch is calling for the compressor or not. The other side reads 0 volts but with a high resistance to ground. The load side from 12 V and to the clutch are fine.

The second is that at high rpms (coming down a steep grade in 1st or 2nd gear) the battery warning light flickers dimly on the dash. It goes away as rpms come down.

Am I seeing indicators of a bad ground? If so, does anyone have the physical locations for me to look at?

[ga traveler]

It sounds like your low pressure switch is on.

[texnet]

Low presssure switch = low freon in A/C. Have it serviced.

By Battery warning light, do you mean the charge light for the alternator or something else? I would thing an 07 would have a gauge.

[tpm64]

ga traveler - I did not even think of the low pressure switch breaking the feed to the relay, but that makes perfect sense. I really need to get a chassis wiring diagram. I will check refrigerant tonight.

texnet - yes, the charge light for the alternator. Voltage output is fine from the alternator. But in thinking about it, the generator was on, which means the converter was on charging the house batteries and the solenoid tieing the house to the chassis battery was engaged. So I wonder if a higher voltage from the converter caused the alternator light to flicker. I need to do some more homework.

Anybody know if the low pressure switch is NC or NO?

[ga traveler]

I would think it is a no. The pressure closes it. When the press. gets to low it opens and breaks the circuit.