high pressure port/low pressure port
 

hi

i have a haynes manual which is very useful, until it showed me the two ports

for the a/c , i want to re charge the a/c with a halfords recharge bottle

but as it says only use low pressure port

the manual pictures the two but does not say which

there is one on the front bulkhead near the rad and one down the side under the steering system top up bottle, i think this is low pressure

but does anybody know for sure

The low pressure port will be in or will lead to a larger diameter line, and that line will be cool when the a/c is on (if there is sufficient freon in the system to provide some refrigerating effect). The low pressure side is the return line from the cold evaporator in the interior of the car to the suction side of the compressor. The high pressure line goes from the high side of the compressor to the condenser ahead of the radiator and from the condensor to the firewall and on to the evaporator inside the car.

It could be that the fittings on the two ports are different types and the charging bottle connector will only fit on the low pressure one.

How do you know it is low on freon? How will you know that you have added the right amount of freon? You can overcharge the a/c, in which case it will not cool properly. You might damage the compressor or expansion valve.

read the undermentioned post on diy recharging kits, personally i would not use one.

http://www.volvoforums.org.uk/showth...t=diy+recharge

indeed , they are a bit of a bodge to say the least when you understand the proper recovery , vacuuming and recharging process ..

and when the bottle and car has reached ambient temperature how is the gas going to move from bottle to car when both pressures are the same ?

I suppose the common auto refrigerant in Europe is R-134a, right? Our USA spec 2004 V70 and 2007 XC90 use R-134a. Personally, I no longer mess with my auto a/c units. I take it to the pro's who have the approved equipment to control discharge of freon refrigerant.

When full, the refrigerant dispensing can has a much higher pressure than the low side of a running auto a/c. There is liquid freon in the can and gaseous freon above it. So to charge into the low side without slamming liquid into the compressor one keeps the can upright.

As charging proceeds the dispensing can gets cold and the pressure inside drops. To restore pressure and speed up charging one can put the can in a container of warm water (not hot).

In the bad old days (short on money and insufficiently concerned about the environment) I used to recharge my auto a/c's with the R-12 freon used at the time. R-12 was an efficient refrigerant and liquified at a relatively low pressure allowing a cheaper compressor. But R-12 was terrible for the stratospheric ozone layer, and I believe it is unavailable legally. In 2007 when I gave away my 1991 Dodge to someone who needed 'value' transportation, the a/c was still cold and it had never been serviced except for a adding a little R-12 every 3 or 4 years. There was a mixed hydrocarbon (no effect on stratospheric ozone) refrigerant which would work in the old R12systems, but was unapproved because it was flammable or even explosive. The only real danger I can think of would have been if there would be a full dump into the passenger compartment and it ignited before the windows could be opened.

I have a set of pressure gauges calibrated in psi and in temperatures for R-12 and R-22 so I could charge my autos with R-12 and my home a/c with R-22.

R-22 was much better for the ozone layer than R-12, but could not be used in auto a/c units because it destroyed rubber hoses. Rubber hoses were necessary to allow relative motion between the compressor on the engine and the condenser and evaporator on the body. R-22 could have been used in autos if they went to an electrically powered compressor mounted on the body, but this would have required a very high output alternator and this arrangement was not adopted (except maybe in some hybrids)

I believe R-22 is no longer manufactured in the western countries, but there are ample stores of R-22 to service older home units. My current home a/c is over 20 years old, but doesn't leak. I have a 30 lb bottle of R-22 in my garage which I will hand over for recycling when my home unit gives up.

there is a little cooling effect, i have knowledge of a/c units but not cars
i have had the unti done before and it was icy cold, so it must have lost some
r 134a somewhere:thumbs_up: