Fixing AC

[Majik]

So here is the deal, I broke off the pressure sensor on my ac line. I was trying to replace a motor mount, and just used a bit too much force. I have ordered a new line with a fitting for the sensor, and a new evaporator. Also the o-rings that go into each connection. I am going to do the install myself, but have an AC shop evacuate it and refill it. Is there a specific order to do this? I have heard to wait to install the evaporator until the last minute, but that would be tough because of its location. Can I install in the same day as I get the ac evacuated, or does it need to be right then? I suppose I can take the old one off and install the new one at the shop. IF anyone has any tips for ac work I would appreciate them.

[JRW]

OK this advice is worth exactly what you paid for it!

I can not think of any technical reason to wait on the evaporator.
IF you were replacing the drier, I can see waiting to install that until you are ready to evacuate the system.

Some factory manual services notes:
...Always immediately plug all open fittings after removal of ac parts... to keep moisture and foreign mat'l out.

I can't find any other significant notes.

HTH

[Majik]

Thanks for the reply, I think I might have some of the terms backwards. The system has been open for awhile now. I havent turned it on, but I am sure it has moisture in it. I bought the replacement line, and what is described as Tank, liquid PN nc1061-500a I was under the impression that this is the evaporator. Is this what I need to replace since the system has been opened? Or is it the dryer? This peice is the cylinder infront of the radiator to the pass side of the car.

[JRW]

The evaporator is under the dash.
It sounds like you are replacing the drier and I would keep that sealed until you get ready to evacuate the system.

[TurboDuane]

Let me preface this by saying, I have extensive AC experiance in my distant past. However, I've not had to do any work on the Miata, so my comments will be in general and not Miata specific.

The AC system is made up of basicly five components:

1) Compressor (it's bolted to the engine and has a belt attached to it)
2) Condensor (the coil in front of the radiator where hot air goes out)
3) Evaporator (the coil under the dash that makes the air cold)
4) Drier (a fat piece of piping that catches crap in the AC system, simular to what an oil filter does for the oil system)
5) Collector (acutally has a different name I can't think of right now) (a big tank that holds extra freon that is always cold and sweating under the hood when the A/C is on) Cars need this due to the fluctuation in rpm's thus freon pressures.

The problem is your system has been open for a while. Therefore, you will need to pull a vacume on it for a while once you've got your system put back together. Pulling a vacume on it helps evaporate any moisture you may have in your system. This is not to be confused with evacuating a system. Evacuating your system means they pump the freon out of the system and recover it in a storage tank. Pulling a vacume however, is when you get a vacume pump (available at most rental places) hook it up to your AC System, and let it run for several hours, if not a day. The longer the better. Once you are done with this phase you remove the vacume pump and let the system stay in a vacume untill you add freon.

If you have moisture in the system, the dryier is supposed to catch it. However, if you have too much, then the drier will be overwhelmd and will probably plug up. Any moisture that gets past the drier will most definately cause a restriction at the restrictor within the Evaporator, causing A/C failure.

[Majik]

OK, I think I will do it next week or so. Here are the steps I am going to take.
1. Install new pipe.
2. Install new drier.
3. Pull Vacuum
4. Surf www.forums.dfwmiata.com for 24 hours straight
5. Unhook Vacuum machine
6. Fill With freon
7. Drive and be

[POS Racing]

For what it's worth : Back in the day when I was young an R-12 was prevalent the rule was if the system was open for a long time you needed to change the dryer. It was filled with a desiccant material that helped to remove moisture if the system was open for a long period of time (like yours Majik) it needed to be changed, since the you can’t remove all the moisture in the desiccant once it had saturated. Another thing that was always recommended was that you changed the orifice tube, which is a filter thingy….

[Majik]

if the system was open for a long time you needed to change the dryer.

which is a filter thingy….

2. Install new drier.

Thanks POS :P

[POS Racing]

Opps I must not have been clear the orifice tube is a separate item from the drier!

Another thing that was always recommended was that you changed the orifice tube, which is a filter thingy….

2. Install new drier.

Thanks POS :P

Did you get it an orifice tube which is the filter thingy!

They look like the items in this kit:


Signs of Orifice Tube Blockages -- Debris, rust or debris in the system may plug up the orifice tube or metering valve that admits refrigerant into the evaporator. If this vital point becomes obstructed, the flow of refrigerant may be restricted or blocked causing a loss of cooling -- and possible compressor damage as well in systems that rely on oil circulating with the refrigerant for lubrication.