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Old 06-27-2008, 05:51 PM
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Exclamation HVAC FAQs for 97-03 F-Series (including Navigator & Expedition)

Thanks to projectSHO89 for putting this together.


Symptom: Loss of control of temperature. May be stuck in one position or may flop open/closed with vehicle motion when starting/stopping.
Problem: Broken Blend Door
Solution: Replace blend door. Requires removal of dash. There are several threads that deal with this.

Symptom: Can’t change temperature. Easily confused with a stuck/broken blend door.
Problem: Stripped Temperature Knob
Solution: Replace **** with a new one from the dealer.

Problem: Can’t find the low side port.
Solution: Remove the cover over the mega-fuse and starter relay. The port is on the side of the silver accumulator can attached at the firewall. Move wire harnesses and hoses as needed to access.

Symptom: Loss of air cooling when accelerating or while cruising.
Problem: A/C clutch slips or won’t stay engaged causing loss of cooling.
Solution: Excessive A/C clutch gap due to clutch wear. Usually, the problem can be resolved by removing a shim from the clutch to bring the gap back into the desired .014-.030” gap.

Problem: Air conditioning cuts out under heavy acceleration.
Solution: On some models, it is supposed to so that engine power is made available for acceleration. Can also be caused by the clutch slipping due to excessive air gap.

Problem: Air flow has defaulted to the defrost vents (either all the time or under acceleration).
Solution: The system is designed to default to the defroster in the event airflow control is lost. Intake manifold vacuum is supplied to the control head, whether manual or automatic (electronic) to operate the vacuum motors.. A very common failure is a split, cracked, or otherwise leaking vacuum line located between the battery and firewall. Other causes include a leaking vacuum reservoir (inside the right front fender), faulty check-valve inside the dash, or other vacuum leak in the system.

Symptom: No cooling. Rapid (short-)cycling of compressor clutch.
Problem: Compressor is turning on and off rapidly.
Solution: System is low on refrigerant charge. Your system has leaked and lost refrigerant. It needs to be evacuated, repaired, and then properly recharged to proper level.

Q. Can I use one of the charge-kits that include a stop-leak?
A. Sure, but you’re on your own. Sometimes they work fine, other times they mess up the system and leave you with a more expensive repair. Do you want to gamble with your $1500+ system?

Q. Can I just charge it up with the kit from Wal-Mart or the auto parts store?
A. You’re violating federal (US) law by charging a leaking system. You’re also likely to either under- or over-charge the system.

Q. I’m recharging the system with one of those kits. How do I know when it’s properly charged?
A. You won’t be able to. You need the low side pressure, high side pressure, and the ambient temperature along with the proper vehicle setup/preparation in order to charge a system accurately. The most accurate charge comes from weighing the refrigerant and charging into a completely evacuated system. You may get it close enough so it works, but you won’t have it at peak effeciency.

Symptom: No cooling. No engagement of compressor clutch
Problem: Compressor clutch does not engage. (Ambient above 45F)
1) System discharged (low refrigerant level). Measure system static pressure. If below 45 psi, repair leak, and properly recharge.
2) Faulty low-side cycling switch on the accumulator can. To test, unplug the connector from the switch and insert a straightened paperclip into the harness connector. Test only for very short duration. If the compressor now engages, the switch is bad (assuming you met the minimum pressure requirement in #1).
3) A/C clutch gap excessive. Measure the gap. If too great, the clutch simply cannot engage. Remove a shim, if possible.
4) Other electrical circuit fault. Includes open clutch coil (should be around 3-4 ohms), failed clutch relay on those vehicles that have one (some control the clutch directly via the cycling switch), open high-side cutoff switch, open fuse that supplies the circuit, a faulty selector switch, or some other circuit fault that will require in-depth troubleshooting.

Problem: That el-cheapo gauge from Wal-Mart says I’m supposed to have 30-40 psi in the system but it shows I have between 80 and 120 psi.
Q. Should I let out some of the refrigerant?
A. NO! That is your system static pressure when the compressor is not running. You need to diagnose why the compressor is not running. See above.

Q. Why does my compressor not run much when it’s cold out side.
A. Refrigerant contracts when it gets colder. This causes the pressure to drop inside the system. When the pressure drops below approximately 45 psi, the system no longer has enough pressure to close the pressure cycling switch. The actual temperature may range from 35-50F but compressor operation should not be expected when the temperature is below 50F.

Problem: The A/C compressor runs in different climate control positions.
A:Generally, it’s supposed to be enabled in all settings except OFF, FLOOR, and VENT. Refer to your owner’s manual.
Old 06-27-2008, 05:51 PM
 
 
 
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