Recharge Airconditioner
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2nd Gear
Joined: Jun 2026
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Recharge Airconditioner
After a minor front end collision, I replaced the condenser on my 99 F-250 Supercab 4×4. Then after verifying no leaks and evacuating the system I started adding R-134a and got nearly 12 ounces in then jumped the connector to the low pressure switch trying to get the compressor to start so I could add more refrigerant. The compressor didn't start so I shut off the engine and disconnected the wire connector to the compressor to try to verify 12 volts. But at that point the engine would only crank not start. But when the connector is plugged back into the compressor the engine (V-10) starts immediately. The compressor is not seized, it can be turned by hand with some resistance. I've worked on other brands of vehicles and never ran into this Crank But NO Start with airconditioning compressor disconnected. Anyone have any idea why the truck won't start with the A/C compressor's power connector disconnected?
Hotshot
Joined: Jan 2004
Posts: 19,763
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From: St Louis
You disconnected the engine's crank sensor, not the A/C clutch connector, by accident. They are easy to mix up.
You're not the first one to do that.
IIRC, the clutch circuit is driven directly by the series circuit of the low and high pressure switches on the early Super Duty trucks. Verify power is getting through both switches.
CJB F24 (HOT in RUN) > Mode switch > low pressure cycling switch > high pressure cutout switch (normally closed) > clutch coil.
One at a time, jumper the switches and see if the clutch now engages.
You're not the first one to do that.
IIRC, the clutch circuit is driven directly by the series circuit of the low and high pressure switches on the early Super Duty trucks. Verify power is getting through both switches.
CJB F24 (HOT in RUN) > Mode switch > low pressure cycling switch > high pressure cutout switch (normally closed) > clutch coil.
One at a time, jumper the switches and see if the clutch now engages.
Last edited by projectSHO89; Jun 6, 2026 at 07:27 AM.
Thread Starter
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2nd Gear
Joined: Jun 2026
Posts: 2
Likes: 0
You disconnected the engine's crank sensor, not the A/C clutch connector, by accident. They are easy to mix up.
You're not the first one to do that.
IIRC, the clutch circuit is driven directly by the series circuit of the low and high pressure switches on the early Super Duty trucks. Verify power is getting through both switches.
CJB F24 (HOT in RUN) > Mode switch > low pressure cycling switch > high pressure cutout switch (normally closed) > clutch coil.
One at a time, jumper the switches and see if the clutch now engages.
You're not the first one to do that.
IIRC, the clutch circuit is driven directly by the series circuit of the low and high pressure switches on the early Super Duty trucks. Verify power is getting through both switches.
CJB F24 (HOT in RUN) > Mode switch > low pressure cycling switch > high pressure cutout switch (normally closed) > clutch coil.
One at a time, jumper the switches and see if the clutch now engages.
Hotshot
Joined: Jul 2013
Posts: 14,291
Likes: 2,197
12oz sounds pretty low as a start charge
the AC system has a pressure sensor that will only allow the compressor to sping if the system has the correct charge.
also need charge oil
once you have the baseline charge by weight....you would use an ambient air temp to charge PSI chart to see if the system has an adequate charge.
the AC system has a pressure sensor that will only allow the compressor to sping if the system has the correct charge.
also need charge oil
once you have the baseline charge by weight....you would use an ambient air temp to charge PSI chart to see if the system has an adequate charge.
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