Engine Size: 4-cyl
Refrigerant Type: R134a
Ambient Temp: 80
Pressure Low: N/A
Pressure High: N/A
1998 Frontier AC idler pulley locked up, broke belt, no big deal (replacement pulley with bearing is $40).
Question is: I printed the wiring diagrams, etc., and the AC compressor and relay, etc. only energize when the engine is running, not when ignition is switched "on" and fan and AC button are engaged.
So is this the truck computer that prevents that circuit to the relay from working with the engine off, and if so: how (or really: where) would one bypass to troubleshoot without the engine running, if I need to do such in the future? Thanks.
Likely it goes through the computer. When it receives an A/C request signal, the computer increases the idle speed and enforces a slight delay for the engine to speed up before engaging the compressor. Also if the rpm drops too low it will drop out the compressor to help avoid stalling. That is why it will not engage with the engine stopped. Avoid jumpering stuff whenever possible. The system can be checked out by probing for voltages rather than jumpering.
Edited: Mon March 19, 2012 at 11:16 PM by mk378
Thank you, makes sense. The service manual for this is somewhat cryptic.
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