Charging AC
03-15-2006, 04:51 PM
#1
Burning Brakes
Thread Starter
Charging AC
My AC is not kicking on a am pretty sure it needs to be recharged.
Freeze switch ok and compressor clutch engaged when I jumped the pressure switch.
The car hasn't been driven very much during the last couple of years (I assume) and am hoping the fluid just needs to be topped off. I talked with my tech and he said he'd evacuate and fill this Saturday (@$60/# of R-12). Not interested in converting to r-134 or use any drop-ins. Prefer to top off rather than evacuate and fill.
Assuming there has always been positive pressure in system, can moisture still get into the system? If there is no assumed threat of moisture, does the system need to be evacuated?
Also, I'm a little unclear about the oil issues. IIRC oil is entrained in the freon and leaks when the freon leaks. How insignificant is the amount of oil relative to the amount of freon that leaks? Is there a danger of having too much oil in the system other than reducing the capacity of the working fluid?
Just trying to get a sense of how this all works so I can weigh the risks and make a best guess in terms of what happens in 20 years of time.
Freeze switch ok and compressor clutch engaged when I jumped the pressure switch.
The car hasn't been driven very much during the last couple of years (I assume) and am hoping the fluid just needs to be topped off. I talked with my tech and he said he'd evacuate and fill this Saturday (@$60/# of R-12). Not interested in converting to r-134 or use any drop-ins. Prefer to top off rather than evacuate and fill.
Assuming there has always been positive pressure in system, can moisture still get into the system? If there is no assumed threat of moisture, does the system need to be evacuated?
Also, I'm a little unclear about the oil issues. IIRC oil is entrained in the freon and leaks when the freon leaks. How insignificant is the amount of oil relative to the amount of freon that leaks? Is there a danger of having too much oil in the system other than reducing the capacity of the working fluid?
Just trying to get a sense of how this all works so I can weigh the risks and make a best guess in terms of what happens in 20 years of time.
03-15-2006, 05:28 PM
#2
Rennlist Member
Your diagnosis sounds correct with those symptoms. The question about oil is hard to answer, depends where the leak is, usu oil is seen, but not necessarily. How long has it been since it was last charged? Older cars have permeable hoses that will leak over time, but were talking 5 to 10 years before a charge is needed. If the charge is less than a couple years old, there is a leak and you should have that fixed first. There is a sticker on the rad, mine holds 37 oz I think and they usu charge you for a whole pound for any part of a pound, so you are looking at at least 2 lbs for freon.
03-15-2006, 05:48 PM
#3
Burning Brakes
Thread Starter
Don't have any history for the car except it sat around with various dealers for about 2 years and driven about 7000 miles the previous 10 years before that.
My tech said he would check the system for leaks. I'm being optimistic in thinking it's a minor leak (i.e., leaked due to non-use). But I won't find out until Sat when we check the system pressure. If it's pressurized below the pressure switch threshold, then I'll consider topping off. Unless someone tells me moisture can enter the system when there is positive pressure in the system - assuming it was pressurized above ambient for 20 years.
My tech said he would check the system for leaks. I'm being optimistic in thinking it's a minor leak (i.e., leaked due to non-use). But I won't find out until Sat when we check the system pressure. If it's pressurized below the pressure switch threshold, then I'll consider topping off. Unless someone tells me moisture can enter the system when there is positive pressure in the system - assuming it was pressurized above ambient for 20 years.
03-15-2006, 06:09 PM
#4
Rennlist Member
Rennlist Site Sponsor
If your tech has the proper equipment, knowledge and credentials to correctly and legally service the A/C, he can remove and recycle any existing Freon. This will clean it of any moisture and contamination. If he can't do that, he shouldn't be servicing the system.
If he is properly equipped, he can recycle the existing Freon, add more and leak test. If there is a significant leak (and at $60/pound, ANY leak is significant!), he can pull the Freon out, fix the leak, and put the Freon back in.
The most common leaks are the O-rings at every joint in the system - they get hard over time, and leak. Tightening the joints won't help. If you put new O-rings in, be sure that they are the new green or blue rings, so if you ever convert to R-134a, you will be good to go.
If there has always been positive pressure in the system, there should be no significant amount of moisture in the system. If there is no pressure, a new receiver/dryer would be a wise investment.
If he is properly equipped, he can recycle the existing Freon, add more and leak test. If there is a significant leak (and at $60/pound, ANY leak is significant!), he can pull the Freon out, fix the leak, and put the Freon back in.
The most common leaks are the O-rings at every joint in the system - they get hard over time, and leak. Tightening the joints won't help. If you put new O-rings in, be sure that they are the new green or blue rings, so if you ever convert to R-134a, you will be good to go.
If there has always been positive pressure in the system, there should be no significant amount of moisture in the system. If there is no pressure, a new receiver/dryer would be a wise investment.
03-15-2006, 07:02 PM
#5
Burning Brakes
Thread Starter
Wally P,
Thanks, read as much as I could before posting, especially your HVAC write up in the CDs.
My tech has come through for me several times. But from other experiences, I don't think I will ever fully trust anyone that works on my car. Just trying to understand what needs to be done.
Thanks, read as much as I could before posting, especially your HVAC write up in the CDs.
My tech has come through for me several times. But from other experiences, I don't think I will ever fully trust anyone that works on my car. Just trying to understand what needs to be done.
03-15-2006, 10:15 PM
#6
Rennlist Member
The reason for the evac and charge is threefold:
1. Check for leaks (monitoring vacuum stability)
2. Insure no moisture in the system
3. Correct charge level achieved
It is not possible to determine the precise amount of freon in an operating system. Pressures will only give a relative level of function based on air temp, ambient pressure, airflow over the condensor and evaporator, etc. It's similar to figuring out exactly how much blood is in your body by taking your own blood pressure.
Adding a can of freon to a low system can certainly get the system closer to design specs, but there is no way to know if you are under or over filled. The only way is to evacuate the system and fill will the precise amount.
1. Check for leaks (monitoring vacuum stability)
2. Insure no moisture in the system
3. Correct charge level achieved
It is not possible to determine the precise amount of freon in an operating system. Pressures will only give a relative level of function based on air temp, ambient pressure, airflow over the condensor and evaporator, etc. It's similar to figuring out exactly how much blood is in your body by taking your own blood pressure.
Adding a can of freon to a low system can certainly get the system closer to design specs, but there is no way to know if you are under or over filled. The only way is to evacuate the system and fill will the precise amount.