Wiring for heater and ac unit

[Victor Balonis]

No power to units

[wdaly]

Could you be more specific?  Does the Fan switch work?  What year car?

[Victor Balonis]

No heater and no ac power good at the fuses 

[Victor Balonis]

On 9/29/2023 at 1:22 PM, wdaly said:

Could you be more specific?  Does the Fan switch work?  What year car?

No power to the units 1985 with a gm Fuze box

[silverstude]

Obviously, the ignition should be on when testing.

First thing you should do is pull the existing fuses and replace them with fresh units.  Just running a continuity test on the existing fuses won't prove they can handle a load.     The A/C and heater were likely to have been used more than any other component and the heat cycle of the that fuse could have compromised it.   Putting a dab of dielectric grease on each fuse leg prior to install will insure long term continuity thru the fuses.  

If that doesn't resolve the issue,  check the continuity of the wiring between the fuse panel and each component, via the switches. First do the fuse to the Switch, if good at the switch, then follow up to to the component. The switches may be the issue. 

 If you have 12V at the fuse and the switch and nothing at the components, then the supply wiring  between the switch and the component is open somewhere.   If you run a bypass wire from the fuse to the compressor get a "click' by  touching the compressor pigtail, the original circuit is faulty and must be replaced.  

The same fuse handles the heater fan motor, so again, check the power at the switch first, then to the component.