another a/c question

I have a 1996 Caravan 3.3L and would like to know what the capacity of the a/c system is. I believe that I am low on R134a chemical. I would also like to know a simple procedure. Can I tell if it is low simply by measuring the pressure on the low side? What should the pressure be on a fully charged system? I have a pressure gauge and fitting and have checked it to be less than 40 lbs. By comparison my 96 Intrepid with a

3.3 engine measures 80 lbs, whether the gauge is coorect or not I am just using it as a comparison Both measured with the engine off.

Thanks,

Reply to
Steve Berry
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The aftermarket consumer re-charge products (Interdynamics) claim that you can tell from just the low-side pressure (with temperature correction needed *only* if the ambient is outside some range - something like 70 to 80°F, IIRC), even though the shop manual procedure uses hi-side pressure and temperature of the metal line coming out of the condensor (a temp/pressure chart is provided with a narrow band of acceptable operation shaded in).

I just went thru this mind game recently on my '99 Concorde, and decided not to trust the aftermarket approximations (I don't want to be penny wise and pound foolish) - bought a real dual gage set just yesterday at Advance ($74). Will be checking charge level and topping it off this weekend.

If an expert on the subject (of which I am not) posts that the low-side method is acceptable, then by all means go with that.

Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my adddress with the letter 'x')

Reply to
Bill Putney

This information is available right under the hood, on a label on the radiator support panel or on the A/C compressor itself.

Pressures measured with the engine off are meaningless.

Reply to
Daniel J. Stern

The easiest way to tell if you are low on refrigerant is to drive the vehicle with the A/C on AND IN RECIRCULATING MODE during a hot day for an hour, then check to see that there is condensate water coming out of the evaporator drain. If the evaporator isn't getting cold enough for water to condense on it, then fall into the evap tray and run out the drain, then it's not cold enough. The human body dumps enough water into the air for this test to work even if your in a very dry environment.

In a damp environment, such as here in Portland, on a warm day I can turn on the A/C at idle and within a minute, the underhood low pressure refrigerant fittings are wet with condensation.

Ted

Reply to
Ted Mittelstaedt

Reply to
mic canic

You have to measure both the high-side pressure AND the condensor temperature, and then look up the correct pressure for the corresponding temperature. The procedure and chart of pressure vs. temp showing the undercharged/normal/overcharged regions are in the factory service manual.

Reply to
Steve

Steve - Do you (or anyone else) have any definite knowledge of how close the cheapy aftermarket method of measuring (only) low-side pressure is to the (assumed to be much more accurate) shop manual procedure based on hi-side pressure and condensor temp? (I did notice in the aftermarket "simplified" method that they do say that it is acceptable without any temperature correction for a range of ambient temperature (something like a range of 70 to 80°F IIRC.) (I had bought the cheapy kit for low-side pressure only, but took it back for a refund before using it and got a real set of gages after thinking about it. Borrowed a digital contact temp. probe from work and topped off my system yesterday and it works great - hopefully whatever had leaked out was *very* slowly over a period of years vs. recent larger leak development - time will tell - I put in 134a laced with UV dye just in case.)

Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my adddress with the letter 'x')

Reply to
Bill Putney

I really don't have any hard data as to the relative accuracy of the low-side only method, but my guess is that its "pretty inaccurate." The reason I say that is that an error of one PSI out of 30-40 psi is a much bigger percentage than an error of 1 PSI out of 200 PSI. The high side just gives you a lot better resolution on the measurement, so to speak.

Reply to
Steve

Bill, I'm not a fan of the temperature test except as a quick check, to be honest. I prefer the method of sucking all the refrigerant out, then adding the exact number of pounds or ounces of refrigerant that are called for by the specs. Also, if you are working with a R12R134a conversion, the factory-supplied table is for R12 and is useless.

However, one big problem with only measuring the low side is that if there's a problem in the system like a blockage that might be creating excessivly high side pressures you won't see them.

Nevertheless I did buy one of those quick "tire checking like" A/C guages, the ones with the green/blue/red areas on the guage, just to see how horrible it was.

With my 1984 Chevy, R134a conversion, filled with exactly the number of ounces of refrigerant called for by the specs, I checked the pressure on the quick check guage and was interested to note that the needle on the quick check guage was at the absolute minimum pressure for an acceptable system. Since the guage doesen't even register with less than 2 ounces of refrigerant in the system, I have to conclude that this guage reads low.

Ted

Reply to
Ted Mittelstaedt

Steve wrote: "I have a 1996 Caravan 3.3L and would like to know what the capacity of the a/c system is. I believe that I am low on R134a chemical. I would also like to know a simple procedure. Can I tell if it is low simply by measuring the pressure on the low side? What should the pressure be on a fully charged system? I have a pressure gauge and fitting and have checked it to be less than 40 lbs. By comparison my 96 Intrepid with a 3.3 engine measures 80 lbs, whether the gauge is coorect or not I am just using it as a comparison Both measured with the engine off."

Try here

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Sarge

Reply to
Sarge

Thanks, Ted. Kind of as I expected. I think I'll stick with the "real" gages and the shop manual method of charging/checking. So far, after topping the system off, my stystem is still performing well at 36°F (recirc) and 40°F (non-recirc) at the vents with all controls max'ed. I hope that continues (i.e., no leaks - especialy in the evaporator which the LH cars tend to have and cost a bunch of labor to replace).

Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my adddress with the letter 'x')

Reply to
Bill Putney

Oh - and I did put in UV dye - just in case.

Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my adddress with the letter 'x')

Reply to
Bill Putney

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