I have been trying to search for someone else that has had this problem with no success. It looks like most of the AC problems can be fixed by removing a ship from the compressor.

I have a 1999 F350 automatic and it only blows warm air. I checked the freon level and it was empty. I went and bought some dye and some freon to put in the system to see if I can find a leak. When trying to add the dye or the freon it will not let me add it. I was doing this with the truck running and when I started to add the freon I could hear and see the clutch engaging and disengaging. What would cause the system to not allow me to add freon?

 

If the system is empty that means there is no vacuum.


The system must have a vacuum to allow refrigerant to be added.


How did you check for the leveL. By pushing a schrader valve?

 

I used a pressure gauge and there was zero pressure.

 

Now that you mention the vacuum, I did change out the 4X4 locking hubs to Warn and may not have sealed off the vacuum line. Could that be what is causing my problem with the AC?

 

No, A/C is its own closed system and has nothing to do with the vacuum hubs or HVAC controls in the dash.

 

Take it into the shop to get it fixed. You're in over your head.

 

There is a high-pressure side (hot) and a low-pressure side (cold) to a refrigeration pump. If this catches you off-guard, you are better off to let the pros handle it. They have the means to pressure-test the system and fix the leak. When they fill it, there is measuring equipment they use to verify that it is not being under/over-filled. They also know which refrigerant to use, of which there are several... and none of them are "Freon" (CFC-12).

I say this more for the sake of the readers, as I get a sense you may know more than the average person about this - because you used the dye to look for leaks. My assertion still holds if you are just reading instructions as you go.

 

If you put some off the shelf refrigerant in there it may contain stuff that will contaminate equipment.

No shop in the world would touch that for you.

 

A system does not need to have a vacuum to take refrigerant. If it did, you'd never have a positive pressure in it at all. However, after a refrigeration system has been opened to the atmosphere, or has lost positive pressure due to a leak, it should be fully evacuated with a vacuum pump to remove moisture and recover any remaining refrigerant. Moisture in a refrigeration system is a great way to ensure an early death of the system. It can cause icing in the orifice tube leading to high head pressure, can hydrolize with the refrigerant and become hydrochloric acid, and can contaminate the refrigeration oil. This can lead to destruction of the compressor or other components.

The on-vehicle vacuum system controls the HVAC duct doors only. It has nothing to do whether the A/C compressor will run or not.

The measuring equipment used to charge a system should be a scale. The system is designed to use a certain amount of refrigerant, and weighing it is the proper method to use while charging. Manifold gauges, thermometer and pressure/temperature charts are needed to verify proper operation.

If the clutch is cycling, the system has at least some pressure, otherwise the low pressure cutoff switch would be open.

Take the truck to someone who is licensed and knows what they're doing. A/C systems are not as simple as the manufacturers of the DIY recharge kits would lead you to believe they are.

 

You should really attend an A/C course.
Now, here is a VERY STRONG rule - you MUST, again let me repeat that, YOU MUST make darned certain that all your hoses are well connected and that none of them leak. You must also make darned certain that you do a minimum 30 minute vacuum. If you have replaced parts, which means you've opened your system to the atmosphere, then you MUST suck it down for an hour minimum. Mine went about 1 hour 20 minutes and was fabulous when complete.

The target for the vacuum is -30 PSi on the Low side (probably will never reach that, so if you hit -28 then you're doing very well), and on the Hi side you want the needle to slam against the PSi Post! Not joking, when you vacuum the system down you need to insure that you have pulled it all the way down and that you have sucked the system dry.

 

Where did I say anything that isn't in line with that?

 

Your first statement said you do not need a vacuum.

 

My first statement says a system doesn't need a vacuum to take refrigerant. You can add refrigerant to an undercharged system without evacuating it first. I did not in any way mean to imply that a system with no pressure should be charged.

 

He stated there is zero pressure so in order to know why, the system must be visually inspected then evacuated to see if any more leaks are there and to establish a good base on which to recharge.

But yes it should be taken to a repair shop rather than off the shelf recharge kits that do more harm than good.


Some places add propane after removing the refrigerant.

 

I always used nitrogen to check for leaks with a regulator. Usually, on a hot day, static psi on both sides around 150 psi. I would put in 150 psi and see if it would hold it or where the leak was.

Now having been in the OP shoes, and broke. If he were to bypass the low psi switch on the accumulator, it would stay on enough to stay running to take in the freon...However, at the cost of r134 these days, I agree that he would be better off to find the leak, and pull a good vacuum to get any moisture out. The moisture will not only cause erractic performance but will wear the internals of the compressor.

Be careful with the dye.....too much can cause high psi spikes and erratic performance as well.