Greetings,

I have a 1990 RX-7 I converted it from R-12 to R134a last summer and it worked fine. Now I can't get it to charge up.

I hooked up a Vacuum pump to the A/C systwm and It will hold 25 pounds of vaccume for over an hour.

The clutch on the A/C compressor kicked in while adding the first can of freon. It would not come on prior to adding the freon.

When I went to charge the system I put in 3 cans of R134a and it will not blow cold. The low pressure line will freeze up, but then it thaws out and the gauge bounces between -15 and +15 pounds of freon.

What should I be looking at to fix this problem? The reciever/drier? the evaperator?

Any input would be appreciated.

Thanks.....

 

I am going to go easy on you, so don't get your feeling hurt. Lets get started, shall we?


First, converting an FC to 134a is a mistake. If you thought it worked well, you should feel an R12 or Freeze12 charged system,
Second, it doesn't matter how long the vacuum held at -25". That vacuum level is inadequate for either a recharge or to check for system leaks. . What kind of vacuum pump did you use? FYI you can rent a quality vacuum pump at Autozone. For Free!

You don't have a proper set of gauges, do you? I am guessing you bought a 'conversion kit'. In the business, we call them 'Death Kits'. We used to call them 'College for the Kids' Kits. Most of the time, these kits + an inexperienced person will kill the A/C system.

Third, have you read the capacity specs for this car? Capacity is 29oz of R12. You put in 36 oz of R134a. While there is no correct amount of 134a that will work properly in an FC, general guidelines for conversion is to use 80-85% of the R12 charge. So somewhere between 23 and 25 oz of 134a would be workable. You put in an entire can too much.


Did you put any oil in the system? If so, what kind?

Have you changed the drier or did you change it last year prior to 'converting' it to R134a?

 

It had R12 in it that blew cool but not cold. I am old enough to remember R12 costing 0.69 cents a can when I charged up my 78 Toyota Celica and it blowing cold enough to freeze a bowling ball.


I used a vacuum pump and gauges from, I am guessing, the 1960's or 70's



I did buy a conversion kit from an auto parts store, I am willing to accept that I may have killed the A/C system,

You are correct, I put in too much, I should have researched it more and not listened to my drunken friends. The R12 was working ok and I did not know about R12 Freeze at the time. I listened to the teenager behind the counter at AutoZone, my own fault, and purchased their kit. At least it is a convertible and I can drop the top. Although, Louisiana summers are not pleasant for someone like me from Minnesota.


I only put the oil that came blended with the R134 cans in the conversion kit.

I did not change the drier, should I be looking for a replacement? That being said, do you have any suggestions going forward? I may have a doner car available to me that my neighbors daughter ran out of oil. It is a 1988 with a 5 speed tranny that I was thinking of buying to do the auto to manuel swap. I may be able to get it for $300 to $500. Do you think the A/C parts are compatible?

Thanks in advance, as I got a PM telling me to PM you, alerting me that you are an A/C guru,
~Todd

 

Thanks for the details. Let's get started.

Do you have a copy of the Factory Service Manual? http://www.cochran-racing.com/FSM/index.html

A couple of thing I need you to checkout. What was the type of oil in the kit? If it was Ester, you are OK. If it was PAG, you are gonna need a total system flush.

I make it a habit of replacing the drier on any system the first time I touch it. I want a problem free dry system and the only way to assure this is to use a new drier. The oils used with 134a are incompatible with the original R12 driers. Ester and PAG oils dissolve the bag holding the desiccant over a period of time, releasing the desiccant beads into the system. They will accumulate at the expansion valve causing a restriction. I think this may have happened to your system. The frosting/thawing symptom is caused by a restriction in the system; merely overcharging won't cause this. Pretty much the only way to get a restriction is the desiccant bag failing. Any driers manufactured after about 1995 are likely the new type of drier that is R134a and R12 compatible. Of course, this really is referencing the oil compatibility.

You are gonna need to take the plumbing apart at the expansion valve to check for desiccant beads.

If this has happened, you are gonna need to remove the drier to the expansion valve and flush that portion. I would also recommend replacing the expansion valve. It is not expensive for a new one; you could also source a used valve from the Parts for Sale section of the board. Typically it is not recommended to attempt to flush the valve. You could try.

Flush the pipes with Mineral spirits and an air compressor. Pour some in, blow out the crud with the air nozzle. Repeat until you are certain that the piping is COMPLETELY CLEAN!

Reassemble the system using new green o-rings. You can buy an application specific kit for the car, but be aware that there are multiple systems but only one kit. A universal green o-ring supply kit is available at Autozone/Oriellyauto/Napa etc. for $25-30. This kit has everything but does not have the correct o-rings for the receiver-drier. If your new receiver drier does not come with o-rings, I can supply them for you. They cost me $1 apiece.

As you reassemble the system, always oil up the orings with Ester oil. Don't leave the top off that ester oil can while you are working, or it will react with moisture from the air. Notice I said react. The old mineral oils would absorb moisture and the vacuum pump could remove it. New synthetic ester and pag oils will react and the moisture cannot be removed. If the oil absorbs enough moisture, it loses its lubricity.

So you know-the drier sourcing is a problem with these cars. There is more than one system installed in our RX7's. Check your drier to determine if the mounting bracket is welded on to the drier or if the drier body is clamped on to car. If the bracket is welded on, I have one for sale in the FS section.
https://www.rx7club.com/2nd-generation-rx-7-1986-1992-parts-194/c-reciever-drier-brand-new-%2433-shipped-898682/
This is for the dealer installed air or may be referred to as the 'US' system. Basically when buying replacement drier and expansion valve, take the old parts in with you and match them up to the new parts.

Pull a vacuum. It must approach 30"of Hg, 29.998" of Hg. I usually leave the vacuum pump on for 30 min or so to assure total evacuation. Close the valves on the gauges and turn off the pump. The system must hold the vacuum at that 30" level. Period. If it doesn't, your freon will bleed off over time. My 90'Vert has held it's charge since 2005 with no loss of freon at all.

I have given you lots to work on here, ask questions if you need to.

Good Luck.

 

change the drier and order a freeze 12 charge kit on ebay, comes with the oil, sealer and cans of freeze 12.. i did this last year works great. Thought i could try being one of the lucky few to do r134 but that didnt go so well.. take it out. make sure all joints and bolts are tight.

 

According to the manufactures website, they use PAG oil in their retrofit kit.
http://www.efproducts.com/faqs.php?faq_id=18

I will have to work on this next week. I have a wedding to go to today, and a crawfish boil tomorrow.

It looks like it is welded on (see picture) I will have to fund my PayPal account to purchase your drier. It will probably take a couple of days.

I am sure I will have questions, but you have layed out the steps here in a pretty clear understandable way.

Thanks....