Air Con Questions?
Air Con Questions?
Hi,
I've got a Pug 306 HDI v reg. It has no Gas in the A/C system and i suspect
there is a leak somewhere. I have access to a Nitrogen rig and also a
refridgerent rig as i'm an aircraft engineer.
What is a safe pressure to test for leaks and how would i go about it? I
notice that there are two charging points, which do i use?
When the leak has been rectified how do i go about recharging and to what
pressure?
Any info is greatly apprecited,
With thanks
orion1210I'm not familiar with your car but the following should guide you. You did
not state what year the car is. There was a change in the type of
refrigerant used around the years 93/94. Before this period cars used R12,
after this period the manufacturers switched to R134a. You can purchase
R134a from auto stores. Only a licensed tech can purchase and install R12.
There should be a sticker under the hood that states the type of
refrigerant you have and the amount the system holds. The sticker might be
found in the following places; literally on the underside of the hood, on
the compressor, or possibly on or near the firewall. To find the leak first
visually inspect the system. Often a leak is evidenced by a black oily
spot (the reason being that the system's oil leaks out and attracts dirt).
If you use nitrogen to test for a leak you would be fine going up to about
120 psi.. If you do use the nitrogen ,or refrigerant, you can mix a bubble
solution out of some water and dish soap and apply it to all joints etc.
and if there is a leak it will form bubbles. Don't forget to check the
compressor's shaft seal. This is a seal where the shaft comes out of the
compressor (it is often an area that leaks on cars several years old). You
will likely have to pull the compressor's pulley to check this area. The
ac system basically has two sides. One is the low side and the other is the
high side. The low side will have the larger diameter tubing and the high
side will have the smaller diameter tubing. The low side is the one used
for charging the system. It is the one that runs from the firewall
(evaporator) to the compressor. Somewhere along this you will find the low
side service port (it could even be on the compressor itself). The high
side is the smaller diameter line that runs from the condensor (by the
radiator) to the firewall (evaporator). The high side service port is
somewhere along this line and is only used to take the high pressure
reading.
After you find and fix the leak you will likely need to add some oil to the
system. This will depend on where the leak is and how bad it is. A fast
leak will cause alot of oil loss whereas a slow leak will loose little.
The area the the leak is located will also determine the amount oil lost.
A shaft seal leak will loose alot of oil whereas a joint high up on the
system will loose little oil.
It would be a good idea to change the drier/accumulator (depending on what
your car has). This is a filter that removes dirt and moisture from the
system (install a new one of these after you find and fix the leak). Any
oil that you add can be put into the drier/accumulator before you install
it.
Preparing for charging the system goes something as follows. First attach
the manifold gauges to the car and a vacuum pump. Open both manifold
valves and start the pump. The vacuum gauge should show a vacuum of atleast
29 inches of mercury after a few minutes. If it doesn't then you still
have a leak. If it reaches this point, or more, let it run for about 20
minutes and then close both manifold valves and turn the pump off. At this
point note what the vacuum reading is on the vacuum gauge and let
everything sit for several hours (preferably overnight). If after a good
amount of time the vacuum needle holds steady then you are ready to charge.
If the needle moves then you are loosing vacuum (still have a leak) and
need to solve that.
Once the above has been done you are ready to charge. First open both
manifold valves and vacuum the system for atleast 1/2 hour (the more time
the better) although one to two hours should be more than adequate. After
this time has elapsed close both valves on the manifold and turn the vacuum
pump off. From this point on make sure that the high side manifold gauge
valve is closed and do not open it for any reason. The reason for this is
that the compressor can put excessive pressure into the refrigerant can and
cause it to explode. Once again, do not open the high side valve. Now you
will need to put some refrigerant into the system to actuate the low
pressure cutout switch. About 50 psi should do it. To do this open the
valve on the refrigerant can and slowly open the low side valve on the
manifold set. Once the pressure reaches around 50 psi you are ready to
finish the process. Close the low side valve on the manifold and double
check to make sure that the high side valve is definitly CLOSED!!! Now put
a thermometer at the center vent, start the engine (run it at about 1500
rpm), and turn the ac on high with the windows open. Then slowly open the
low side valve on the manifold. Keep adding refrigerant until you get close
to what the stated charge level is on the car's label. Some of the results
you should see are as follows: A vent temperature somewhere between 35 and
50 degrees farenheit, a low pressure somewhere in the range of 30 to 40,
and a high pressure reading somewhere near 200 to 250 (a rule of thumb is
around 2.5 times the ambient air temperature). Note; all of the these
readings will vary somewhat depending on the type of car and what the
temperature is that day. The hotter it is the higher they will be, and visa
versa. If for some reason the pressure readings vary greatly out of these
ranges at any time (especially the high side), then seek some additional
help. Such a situation would be and indication of a problem and could
cause additional damage to the system. Final Note: A do-it-yourselfer can
only can only get within acceptable ranges when fixing an ac system. To do
it precisely you would need an ac tech's tools (refrigerant scales etc.)
but this does not mean it can't be done without satisfactory results. Good
luck and if you have any additional questions post them.
MaccThanks mate... I never realised that it was such an 'ART'!!
I'll tackle the leak checks first i think.
What type of oil and what amount should i use?
Thanks again
orion1210I don't know what year your car is and what type of compressor it has but
you should be able to find the type and amount of oil at this site:
http://www.aircondition.com/dsmobileac/index.html
Note: The compressor should have a label showing the manufacturer and a
model number. Also, just because you had leak don't assume all the oil
leaked out. As I posted earlier determining the amount of oil lost is only
an educated guess. There is no method to accurately determine the amount
lost. Guessing the amount lost depends on where and how bad the leak is.
Once you find the leak post where you found it and how bad it is and we
should be able to help you determine how much to add.
The following website has some good information such as temperature
pressure charts etc.(should be helpful): http://www.aircondition.com/
Finally, the the following site is a car airconditioning forum where you
can gain alot of knowledge and post questions:
http://www.acsource.net/acforum/
Good luck with your fix and if you need any further help feel free to post.
MaccYour Message
