I bought the car back in '99 and the AC has never worked. I figured out why several years ago when I changed the radiator. Because the receiver/dryer is in the way, you have to push it out of the way. When pushing the receiver/dryer back, the bolt head on one of the two bolts at the top of the unit popped off! There appeared to be glue (epoxy) residue underneath the bolt head. I'm guessing that someone overtightened the bolt at some point breaking off the head. They attempted to fix it with glue of all things, but all of the refrigerant probably vented into the atmosphere after the bolt head broke...
In any case, I extracted the broken bolt and replaced it with a new one and simply never used the AC (since at that time I was considering selling the car). I've decided to keep the car and I'm looking to get the AC working again. I'd like to convert it to R134A. Since there is no R12 in the system, can I simply buy one of the R134 conversion kits and do it myself? Should I get a new receiver/dryer? Are there special tools required to flush the mineral oil out of the system? I have no AC experience so any help would be greatly appreciated.
Minimum requirements for converting a system to R134a.
If system has any refrigerant R12 left in the system it must be reclaimed by an approved recovery machine.
Accumulator/drier must be replaced with an R134a compatible replacement. Conversion fittings and label must be added to the system. Label should have the amount of R134a used and quantity and oil type listed. If vehicle is not equipped with a high pressure cut off switch it must be added. That is the required minimum! While complying with the EPA laws may not provide the best performance.
Flushing the system to remove the mineral oil and debris should also be done. R134a and mineral oil do not work well together so leaving it in the system with R134a is not recommended! O-rings should be replaced with either NBR or HNBR replacements. Adjustment of the pressure cycling switch may also be needed to achieve the best performance. In some cases an upgrade of the condenser may be required to achieve the original performance. In many cases the parallel flow condenser will not be available as a direct replacement. Using a universal parallel flow is an option. A new custom hose set would be needed for the different style fittings used on the various parallel flow condensers.
There are many different suggestions when charging a R12 system with R134a. System must be evacuated before starting the charging procedure. I suggest you start with about 70 percent of the original R12 charge and add an ounce at a time until vent and pressure readings reach the best available results. Remember it is easy to over charge a system with R134a so patience is important.
SO...first thing to figure out is whether you have the Nippondenso system or the MANA system. You'll need to know so you can get the correct parts. You can tell by looking at the sightglass. Driers are hard to get for the MANA system. Redi-Aire made some, but apparently they didn't machine the o-ring openings correctly, and they leak. Ray Crowe at Malloy Mazda told me he had a batch of MANA driers made up a year or two back, so you can probably get one from him. The Nippondenso drier can be had from the forum sponsor, as can the expansion valve for either system.
Good news is:
94RX-7, thanks for the detailed write up. Here's a picture of my drier.
Can you tell which system I have?
That is a MANA system. The Nippondenso system has the sightglass in an aluminum block that sits directly on top of the drier.
94RX-7, what are your thoughts regarding Freeze-12? In order to fully flush the AC system will require a full teardown, which I won't have the time to perform anytime in the near future.
Can I get away with replacing the drier (Ray does have them for $95), adding some ester oil (it should be compatible with the original mineral oil right?), evacuating the system with an AC vacuum pump, and filling the system with Freeze-12 (which I believe is a combo of R134a and R142)? I'm looking for something that will last through this summer...
It's 80 percent R134a. In my opinion you have to follow all the flushing requirements to use Freeze12 just like you would with R134a.
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