AC port under hood

  • 2008 FORD FOCUS
  • 120,000 MILES
Any way to add Freon to port under hood. Thinking it is high side port.
Do you
have the same problem?
Tuesday, July 11th, 2017 AT 5:19 PM

1 Reply

Sounds like this is best left to a professional. The do-it-yourself cans use hoses that will only attach to the low-side port. If you were able to connect it to the high-side, and the AC system was working properly, there is a good chance the little can would explode. Refrigerant is extremely dangerous to work with. It can cause frostbite and blindness. Experienced professionals wear gloves, safety glasses, and a face shield. At a minimum, you should wear safety glasses.

You did not list any problem or symptom, so I cannot address that, but I can offer some observations. Most Ford AC system hoses use quick-connect fittings. They go together real fast on the assembly line, which is all that is important. They almost always leak very slowly. It is common to have to recharge the system every two to four years. Chrysler has used a sight glass, so you can see when the system is fully-charged, since the 1960's, and they are very accurate. Ford started using sight glasses in the mid to late 1980's. The problem is when the system is fully-charged, there will still be vapor bubbles seen in it. In fact, you will never get rid of those bubbles until the system has been seriously over-charged. That is much worse than having an under-charged system.

An AC system works on the principle of a liquid becoming real cold where it turns to a vapor, and you want that to be right in the middle of the evaporator in the dash. That's where the incoming air blows through the fins and gives up its heat. When enough refrigerant is lost, the liquid that is left turns to a vapor in the hose under the hood, and that's where it gets cold. That does not do anything for your comfort.

When there is too much refrigerant in the system, the evaporator is filled with liquid, so very little cooling takes place there. Instead, it turns to vapor in the hose under the hood that is going to the compressor. That also does not do anything for your comfort, but what is worse is that liquid can slosh into the compressor and destroy it. Compressors can only compress a vapor, not a liquid. Home refrigerators will be damaged with as little as two ounces of overcharge. Car systems are designed to handle some over-charge to accommodate bouncing and tilting, but an excessive over-charge still must be avoided to prevent causing damage. This is definitely not one of those "some is good, so more must be better" situations.

The problem with that over-charge is except for Chrysler products, there is no way to know how much refrigerant is in the system now, or when it is fully-charged, unless you recover all that is in there, then pump in the exact measured amount. The gauges on the do-it-yourselfer kits only tell when there's enough to be effective. Even the professional gauge sets don't tell much of a story because pressures in the system are a factor of how well the compressor is working and how fast it is running. To explain further, when the system is at rest, it is purely a coincidence, but a useful one, that system pressure will be very close to outside air temperature. Once the high and low sides have equalized, if it is seventy degrees in the shop, both pressure gauges will read very close to seventy pounds.

At first you might assume if some refrigerant was bled off, pressure would go down, after all, that is what happens with a tire. But in the AC system, part of that refrigerant is liquid, and it is the pressure that keeps it that way. Once you bleed off some gas, pressure goes down, that allows some liquid to vaporize, and doing so means it expands a real lot. That makes the pressure go right back up again to seventy pounds. No matter how much you bleed off, the pressure will stay exactly the same, until there is no more liquid left to vaporize. Tire pressure goes down when you bleed some air off because there is no liquid in them.

The same is true when adding refrigerant. That makes the pressure go up, and that forces more to remain as a liquid. Condensing to a liquid lowers the pressure right back to where it was. In fact, no matter how much you add, the pressures will remain the same when the system is running, until it is filled with all liquid and no vapor. If you could reach that point, pressure would suddenly shoot up with catastrophic results. No one has ever lived to tell about that!

So your issue now is if your system really is low on charge. The symptom would be the compressor cycles on and off too often and too quickly. Along with that, you may see thick frost, or ice, forming on the hose going into the firewall. If the compressor never turns on, it could be disabled by the low-pressure cutout switch, or there could be some totally unrelated electrical problem. If there is no pressure left in the system, there is a major leak that must be located and repaired. If the compressor were to run in that condition, it would draw the low side into a vacuum, and that could suck in outside air. The humidity in that air can do a lot of damage. If a droplet of water was to circulate in an otherwise properly-working system, it would freeze at the expansion valve or orifice tube and block the flow of refrigerant. That is a common cause of intermittent loss of cooling. It can take as much as an hour for that ice to melt and allow refrigerant to resume circulating.

What is worse is water combines with refrigerant to form an acid that attacks metal parts. That mainly corrodes holes in evaporators and condensers. To prevent this, we always pump the system into a vacuum for at least half an hour before pumping in the measured amount of refrigerant. Water boils at seventy seven degrees in a vacuum and can be easily drawn out. If there is still some pressure in your system, it is not necessary to pump it into a vacuum, but there is no way to know exactly how much refrigerant is in there now.

To identify the ports, start at the compressor, and follow the hose to the condenser in front of the radiator. That is the high side. The port can be right on the hose connection at the compressor, but it is more commonly found after the condenser, on the hose going to the firewall. That hose often ends inside a housing where it is hidden, but that is where the low side starts. The evaporator is part of the low side, as well as the hose leaving the firewall and going back to the compressor. You will find the low-side port on that hose, and possibly right on the connection at the compressor.

The two ports are different. The do-it-yourself charging hose will only fit on the low-side port. When you are done, be sure to reinstall the black plastic cap on the port. The valves in those ports leak. Their only purpose is to hold the refrigerant in long enough to give you time to install the caps. Those caps are what do the sealing.
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Tuesday, July 11th, 2017 AT 10:21 PM

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