2000 Windstar A/C recharge

[stryder1]

Early last summer I took my windstar into a repair shop because the A/C wasn't working. They said my system had no refrigerant in it so they did a vacuum test and it was fine so they refilled my A/C with R134a and some dye and I took it back after about 2-3 weeks. They looked it over and said they couldn't find any leaks so $300 later I have A/C. It worked fine for the rest of the summer and fall.

This summer again the compressor won't kick on some I bought one of the DIY kits and hooked the gage up to the low port and it read 0. I proceeded to start refilling the A/C with one of the R134a cans and the compressor kicked on but the pressure kept building to the point the compressor kicked off and then the pressure dropped back down and the compressor came back on and built up again into the red zone and then kicked off and the pressure dropped back down. It continued to do that so I turned off the A/C and need some advise as why it is doing that and what to do next.

Thanks.

[tomj76]

If the pressure started at zero, then it will need about four cans (48 oz) of refrigerant to refill the system (depending on if you have rear A/C, which requires a little less).

In normal operation the A/C cycles on/off depending on the low side pressure. It turns on the compressor if the pressure drops below a certain value (I think it is 22 psi), then runs the compressor until it exceeds another value (I believe 45 psi). Those numbers are available in the service information.

You are probably seeing the system run for short intervals, which is a symptom of a low charge. Also, you should make sure that your cooling fan is running at all times while the A/C is on. Also, you can purchase a black light bulb for a few bucks at WalMart to look for any system leaks (the flourescent dye).

You will need to keep adding refrigerant until the pipe entering the firewall AND the pipe entering the accumulator (large black canister on the passenger side) turns cold enough to collect condensation. It's probably a good idea to add 2 oz. of PAG oil as well.

[stryder1]

Thanks but as mentioned I did start filling it and the low side pressure just kept climbing over 50psi then the compressor would shut off and the pressure would drop back to 20psi and the compressor would come back on and take it up to 50psi again. As I added more refrigerant the pressue just kept getting higher on each cycle so I stopped filling and let it cycle for a while thinking it would start leveling out but it never did so I shutoff the AC.

[tomj76]

I had the same problem this spring.

First of all, make sure your cooling fan is running. If it is not running, you can't charge the system (the cooling fan removes heat from the refrigerant, keeping the pressure down).

The cycling that you see is normal even with a low charge. The Ford service manual explains (and give charts) for how often the cycling should occur in a normally operating system. Strangely enough, the pressure doesn't change that much as you add more refriegerent. The main determinant of the pressure is the temperature of the refrigerent.

With the system operating, feel the high pressure line before it enters the condesor coil. It should be very hot. Feel it where it exits the condesor line. It should be still hot/warm, but not nearly as hot as the other point. Feel the line where it enters the firewall, after the expansion orfice. It should be very cold.

If you find these conditions, and the line returning from the evaporator coil is not also cold, that's a very good sign that the charge is still low.

[stryder1]

Thanks for the reply.

It was strange because as I added more refrigerant the pressure just kept getting higher before it would kick off and I was afraid of blowing the compressor.

Does your still do that after all the refrigerant was put in or does it start it to regulate to a more constant state.

I had to fill my grand prix 2 years ago and it never did this. As I added more refrigerant the pressure just kept going up until it was in the green zone on the gage.

Thanks.

[serge_saati]

Don't add more, you'll damage your compressor.
You should have probably liquid that have build up in the compressor line, between evaporator and condenser. Maybe the air dryer doesn't work properly, or something else.

This is not uncommon with A/C, and they often lead to damage.

My suggestion is, drain all refrigerant in the system, especially in compressor, clean all the system, check the dryer. Then charge the A/C completely. It should work.

It's important that all fans work fine when the A/C is running, if not you will have problems again. Never let the fan running to the lower position. Always 2 or 3.

Also clean your condenser.

[tomj76]

As I added more refrigerant, the low side pressures did not change much, only the cycling times.

As mentioned, there are other potential causes for this behavior. For example, water vapor in the system will condense at the orphice and prevents flow, but there are ways to tell if this has happened. The ice can't stay on the orphice if it warms up, so there always must be some flow through the clogged orphice to maintain the ice. You will be able to feel the pipe at this location and tell that it is cold.

There is no doubt that the system won't work right if it only has 12 oz of refrigerant. It takes about 48 oz for the system to have enough refrigerent to work correctly.

The temperature and pressure of refrigerant are closely related by the properties of the refrigerent. For any pressure, the boiling point is fixed. As the pressure rises, the boiling point also rises. When the system is in operation, the pressure on the low side will drop, the pressure on the high side will increase, the compressed refrigerant vapor will flow from the compressure (at a high pressure and temperature), through condensor (where excess heat is removed to condense the high pressure gas, and additional heat is removed to cool the liquid somewhat). The liquid refrigernet then flows through an expansion valve (orphice) where the pressure drops and the liquid begins to boil. Since the refrigerent is now at a low pressure, the boiling point is much cooler. It takes energy (heat) to boil the refrigerent, and that heat has to come from the pipe (and the air around the pipe) to make it boil. This makes it feel cold. The liquid then travels through the evaporator where the car's interior air moves across the heat exchanger to boil more of the liquid refregerent. If all the refrigerent boils, then it's temperature begins to increase (and you get warm air from the vent). If there is a large volume of liquid flowing through the evaporator, then a lot of air can be cooled off, but if the amount of liquid is small then the air will not cool off much before all the freon has boiled off. What remains of the liquid/gas mixture goes to the accumulator where the liquid is separated from the gas, and only gas is allowed to enter the compressor.

The system cycles to regulate between different ambient conditions and cooling loads. If it kept pumping when when there was no cooling demand, then the heat in the refrigerant would continue to drop until most of the refrigerent was liquid, damaging the compressor. When the A/C fan is set to a low speed, the compressor only needs to run for a few seconds with long pauses between to produce enough liquid refregerent to maintain the demand, but on a hot day with the fan on high, the compressor will run for longer periods with less time between cycles.

If the cooling fans are not operating, then there is no heat being removed from the refregerant, but it continutes to gain heat from inside the car. The compressor is forced to cycle to avoid pressures that will exceed the operating limits. This is why it important to verify correct operation of the cooling fan.

[serge_saati]

That's very rich in information.

The only thing that is not exactly true, is that the system doesn't necessary need 48 oz to works. I already make an A/C working w/ only 12 oz (from 0). Of course, it was not very cool, and takes much time to cool, but it cools.

And the pressure never exceed 45 psi.

Just a question stryder, do you charge it at the low-side or high-side port? If you did at the wrong place, it could cause this kind of problem.

[searcherrr]

For maximum compressor run time turn the dial to max a/c and coldest temperature selection available in the cabin. This will run the compressor long enough to take your freon charge I'd imagine.

Though, these things are old.... I'd ensure any points of potential clogging are replaced if you are going through all the motions of this and bought a kit.

Orifice tube is one of them, Possibly the receiver drier / accumulator too & expansion valve. You have all 3 on your 2000 according to RockAuto.com.

[tomj76]

If you run an A/C system on 1/4 the recommended charge, you run the risk of damaging the compressor. The reason is that the refrigerant carries the lubration to the compressor pump and it also keeps the pump from overheating. A grossly undercharged system is going to leave the compressor less lubricated and less cooled than it should be.

Incidently, GM air conditioning systems self regulate in a completely different way. While there is still a high pressure cutoff switch, it's maninly a safeguard/upper limit mechanism. Instead, the compressor pump has variable compression. The pump adjusts the amount of compression based on the operating conditions. This might be why your seeing different results when you add the refrigerent.

[serge_saati]

Try to test the freon pressure when it's cooler outside (like 72°F), to see if it acts the same.