hey a/c guys...
 

this isn't so much a rotary thing, but whatever.

so i got the a/c charged in my fd (r12), but the compressor cycles on and off way to fast. it'll blow cold for a few seconds, then the compressor will switch off. it's building too much pressure.

i have a compressor (134a) from an rx8 laying around. it's physically smaller--good for the fd engine bay.

so assuming the pulleys lined up and the thing would actually work, would it be better for me to use the newer compressor with r12, or just convert the whole system to 134? 134 is cheaper and all that, so cool beans. but would running r12 freon in a 134 compressor hurt anything? the system will be totally evacuated before it's filled.

also, i know the lines are different, but that's no biggie. there's a local hose shop that can whoop up anthing i ask them for.

thanks

first off, i'm no expert, but i have done the foot work on a fair number of ac jobs.

to convert to r134 you have to use AC flush through the whole system, blow it through with compressed air, and replace the filter/dryer... and it's recommended to replace the o-rings all around too. the oil has to be drained out of the compressor and 134 oil should be put in it.

if you're going to replace the compressor go ahead and go all the way with the 134. don't forget it uses a different oil too, some comps/dryers come with it in there. when i've done it with all the proper supplies it's been from 4 hrs up to a days work depending on the car and what is leaking.

i'm dreading that phase of my project FD. the engine/twins are fun though :)

nothing is wrong with the system, other than the compressor is crusty.

let me phrase the question a different way--

would it be more beneficial to replace the fd compressor with a stock unit, or try to run the rx8 compressor on r12?

IMO, just replace your shot compressor with a rebuilt/new one for an FD. I don't really think there's sense in TRYING to make something else work, when you know there is something out there that WILL work. Know what I mean?

If it's cycling on and off way too fast, you may have a blockage of some sort somewhere in your system. My guess would be either the evaporator or condensor. Look at the condensor closely, are any fins bent? Also, it should be cold uniformly. If there are any spots on it that are warm, that's where your blockage is. Replace it and your system should be good. Or your built-in pressure sensor could be malfunctioning.

I'd bet on a blockage somewhere though.

bent fins on the condensor don't cause blockage in the system. i'll have a look at all the piping, though.

If the system is overcharged the compressor will cycle like that. I would make sure its not overcharged. This is a common problem when you charge a car that is cold. If you think there is a blockage check the high/low pressures.

As far as converting the system im not a certified A/C tech but im pretty sure you can just convert an R12 system to 134 with just the adaptors so there really would be no need for the compressor unless the one you have is bad.

If its building to much pressure chances are you have to much freon in the system, the a/c fan isnt coming on, or you have a plugged up orfice tube.

i'm not ruling out any blockages, but the freon is freshly charged... perfect level.

but the shop i went to said it was the compressor, so i'm not trying to figure out what's wrong with it. i'm more trying to figure out whether to use an fd compressor, or the newer, smaller, more efficient rx8 compressor.

How do you know its perfectly charged? Did you measure it? Sounds like a low/ high pressure switch or bad expansion valve.

Just reread above post sorry I dont know
Johny

I know this. But if there are a lot of bent fins, and your condensor is in bad shape... well, I'll let you think about it from there.

James

I've never seen a compressor cause high cycling rate. You really need to find out what your low and high side pressures are, and what they are doing when compressor is cycling. My guess is that IF your freon charge is correct, your going to change the compressor and have the same problem.

I agree with this. Have you checked to see if the A/C fan is coming on when you turn on the A/C?? A guy charged a car that wasnt at ambient temp at my work the other day to perfect levels. But then when the system got hot it was cycling just like you mentioned because the pressure was to high. I suggest getting the car up to operating temp and get your High/Low pressure levels. That will pretty much tell you whats going on. But i dont think your compressor is bad unless its leaking or the clutch is making noise.

Evacuate the system again and recharge it by weighing the refrigerant in. There is a tag under the hood that will tell you the exact amount to install. This is the ONLY acceptable method for charging an automobile A/C system. Any other method and you are just guessing. A proper A/C shop will have a machine that will remove the refrigerant in your system. After any repair work, that refrigerant can be returned to the system. Most times though its best to recharge with fresh refrigerant. I`m an A/C service tech for residental and light commercial equipment, 25 years in the business with Type Universal Refrigerant Handling Certification. I don`t have Automotive Cert but have done the work with the correct equipment for a number of years on my own car.

BTW R12 is damned expensive since it is no longer produced in the US.(Motreal Protocal) What did you pay per pound for your recharge. I know the second gens take 1.75 lbs. I spent over $100 just for the gas when recharging mine this year.

i don't have any equipment to do a/c (besides my ghetto 134 charge kit i got from autobone), so i took it to a shop. the switch is fine. it's just building too much pressure when it's on. gets in the upper 400's, then the switch trips.

if i have it idling with a fan on the condensor, it stays on a very long time before it cycles. if i have the engine revved up (2-3k), it switches off after ~5 seconds.

why would u have to convert to 12a it stopped in 92 r134 is 93 on

Dave, If you lived on the east coast You and I could do a lot of tradin work.

It sounds like the TXV (Thermal expansion valve) Its pretty cheap but you have to evacuate the system, dismantle the evap. and vacuum and then recharge.
There is a replacement for R-12 its 414b (hot shot) ita a little cheaper. cools just as well.

I personally dont think the compressor is bad if she'll pump up to 400 normally thats a good compressor.

Easy fix; Tell everyone its a race car and dosen't need A/C

Good luck

Johny

Im convinced its either A) Your overcharged B) Your not pulling enough air through the condensor (Both fans are not turning on) or C) You have a blockage. I could probably tell you more if you had the low side reading. I would tell you to come down and i would look at it for ya for free but i dont have any R-12 gauges anymore.

I looked on alldata for an Orface Tube but it appears FD's dont have one.

low side was still too high, iirc.

charge is perfect, and it doesn't matter if both fans are on with another fan across the condensor.

the a/ was inoperable for a few years, although it still held charge. would a clogged filter do this?

Dave,
The TXV if its a 3rd gen FD01-61-J14 also change the filter/dryer, I think these parts are availble genericly at local auto parts store

any tests i can do to make sure it's that befor ei get the system evac'd? r12 isn't cheap, and the shop labor isn't cheap either, so i wanna do it right this time.

i couldn't afford to do it right the first time, but i could afford to do it twice :p:

They should be able to evacuate the r12 charge, and put it back in after the dryer and TXV swapout.

I think on my FC it cost me $96 bucks for TXV and dryer. If the compressor isbuilding pressure then it almost has to be a restriction. The txv's job is to open and close depending on temp. Also could be in the dryer. Its a good Idea to change both anyway.

I agree with this one. A fellow A/C man.

it will be done. however, my new bumper won't let any air across the condensor, so i gotta cut a hole in it and throw an aux fan on the condensor. after i do that, i'll fry the big fish and hopefully freeze my balls off :)

t66, 87 octane, icy cold a/c... gotta love that idea.