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Another DIY A/C charging/recharging question S90-V90 1998

I have several areas I need to focus on now that the winter is finally gone. One of them is slow leaking A/C. I have been recharging the A/C system in my wife’s S90 myself for the past two summers. In 2001 I did it just once, I believe. The freon stayed there for the whole summer. Last summer I had to recharge three times. I expect that this summer I will have to recharge the system even more often. But that is actually not my question. I want to know what is the best way to tell how much of freon I need to put in. Last fall I bought a two-dial (low/high pressure) A/C manifold gauge, but I don't have vacuum pump. So, I can not evacuate the freon from the system; I can only add new freon when the system is running low on freon. Here is what I did tonight. I connected the manifold gauge to the low pressure side and the original pressure reading was in the high 20’s or low 30’s (psi). The compressor was off and not cycling. Then I started to add R134a which activated the compressor. It did not cycle much. Maybe three or four times. After that it stayed on all the time. The pressure settled at about 35 psi. I almost emptied the whole 12oz can of R134a. When I was shaking the can I could fee that there was a little amount of freon left, but it did not want to go in. I waited maybe 4-5 minutes and then shut off the system. So, after the recharge the compressor was always on, the low side pressure was about 35 psi. What does it tell me? Any idea? Do I need to try to add more to the system? (The outside temperature tonight was about 81F. Not very humid.) I am OK with continuing adding freon to the system, but I obviously don't want to overcharge it...

Raphael








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Another DIY A/C charging/recharging question S90-V90 1998

Get some "PAG" oil with a floresing dye and put an oz or 2 in with the freon. That will help find the leak. More than likely, the compressor is the source of the leak. Check to see if there is a residue of sticky oily stuff from the leaking PAG oil on the housing. If so, be sure to add a couple of ounces of oil anyway to keep the thing from siezing.

The only way to get the optimum charge is to evacuate and then put in the correct amount by weight.
--
'96 965 with 16' wheels at 101K. Had '85 745 Turbo Diesel for 200K.








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Another DIY A/C charging/recharging question S90-V90 1998

PAG oil is different from Ester oil, right? Is PAG oil better for R134a?

Yes, I know that that the best way to charge the A/C system is to completely evacuate old stuff and then put new stuff in. Unfortunately I don't have vacuum pump. Maybe I need to start looking for one.

How do I "force" the whole 12oz can of R134a in the system? Should I rev the engine while charging to increase compressor suction/pressure? Should I wait for even hotter weather? Should I just keep charging for a longer period of time(10 min, 20 min)? Any other techniques?








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Another DIY A/C charging/recharging question S90-V90 1998

Don't "force" the rest of the R134 in. You can over charge your system which is far worse than underscharging the system.

As jbowers stated, you can't accurately put in the correct volume unless you evacuate the entire system

The pressostat on these cars are set to turn the compressor on when the low side pressure drops to 25 psi and turns the compressor off when the low side pressure reaches 45 psi. The time it takes to do this (cycle time) is a function of the charge in the system and the ambient temperature.

DEWFPO
--
1998 S90 062,925 1995 964 145,750








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Another DIY A/C charging/recharging question S90-V90 1998

Thanks! Based on the numbers you provided I can at least confirm that my pressostat is working. I now also understand why the compressor was not cycling when I charged the system: the pressure was always around 35 psi and did not reach the point (45 psi) when it cuts itself off. Could it be because it was too hot outside? Should I try to measure the pressure on a colder day? Generally, what is the relationship between the outside temperature and the pressure in the A/C system?








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Another DIY A/C charging/recharging question S90-V90 1998

RK,

There are many conditions that affect temperature and pressure inside your AC system.

I do not know how to cut and paste jpg's into this form, so if you send me your e-mail, I will send you some charts of an older Ford R-12 System for illustrative purposes. R-134 systems will be similar but slightly different.

DEWFPO
--
1998 S90 062,925 1995 964 145,750








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Another DIY A/C charging/recharging question S90-V90 1998

That would be great. E-mail: rkuznetsovski@yahoo.com. Thanks








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Another DIY A/C charging/recharging question S90-V90 1998

Higher outside temperature => higher AC system pressure.







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