2001 Grand Marquis A/C issues

[jdm71]

2001 Grand Marquis a/c stops cooling when you stop. I've checked the freon level and it is good. Any ideas on what I should be looking for?

 

[franksta]

Mine is a 2004 so I don't know if they used electric cooling fans in '01. Are they running?

 

[jlee]

How did you check the level?

 

[Zenmervolt]

Leaving aside the fact that automotive systems are charged by weight and it's literally impossible to verify the precise charge without evacuating the system, if it's cooling fine at speed but not when stopped there are a few possibilities.

The first thing I'd look at is whether the fans are coming on. The A/C should force the radiator fans to run. Generally they will run at low speed until triggered for high-speed operation by a pressure sensor on the high-pressure side of the A/C system. If the fans aren't coming on, the condenser will heat soak when sitting still and you won't get cooling because the condenser cannot shed heat. This may also cause the high-pressure cut-out switch to trip and turn off the compressor if the heat soak is severe.

If the fans are coming on and you're still not seeing proper cooling at idle, it's possible that your system is improperly charged. If you can get cooling by revving the engine while stopped in neutral, this can indicate a low charge. By revving the engine (to about 2,000 RPM generally) you are speeding up the compressor and allowing the system to work more efficiently, which can overcome a slightly low refrigerant level.

NOTE: If the system does seem to be low on refrigerant, do not attempt to top it off on your own. Automotive A/C systems are charged by refrigerant weight and the only way to get it right is to have a shop evacuate the system and then charge the correct weight. (Theoretically, one could also charge by subcooling or superheat depending on whether it's a TXV or orifice tube system, but that's well beyond the skills of the average home mechanic.) You cannot charge properly based on line pressures.

If the fans are coming on and revving the engine doesn't help, you'll need to have a proper tech look at it because further diagnosis is not really possible based on symptoms. You have to hook up a proper set of manifold hoses and check system pressures under a variety of conditions. While line pressures can't be used to nail down a precisely correct charge, they are very useful for determining what sort of fault is present.

ZV