AC was not working right and dropped it off at the dealer to be fixed. Said low on charge so had to be converted to 134 as R12 not available anymore but not to worry it will work fine. I voiced my concerns and that with some looking it can be found. Assured all would be fine with the 134 and results are 64 degree outlet temps on a 76 degree day.. I used a high quaility temp sensor to measure and allowed 5 minutes for it to stablize. AC had been set on high and recirculate for 15 minutes prior to measuring temp. Humidity was 70% if that matters. To me this is a non player in any way. They changed the compressor oil the valves in the system and added a leak check dye and reported the system has no known leaks they could find. PO had jumpered the compressor cycling switch to make it work previously and it blew very cold air so doubt if it is an air blend door or anything like it. When I found this removed the jumper so as not to kill compressor and of course the compressor short cycled and very little cold air. The sticker on the car calls for 2.25 lbs.(36 oz) of r12 and the sticker they added says they charged it to 2 lbs(32 oz) of r134. I have read and don't know for sure if true that when converting you charge to 80% of the r12 charge. If that is true then I would think 28.8 oz the correct number.

Can overcharging by 3 oz r134 cause my problem? Or is this destined to continue to be a problem of poor performance due to the conversion.. BTW my window AC in the office blows 50 degrees on the same day..LOL
Dave

 

I had my 87 converted to R134a by my shop and I they got a reading of 39 degrees at the center dash outlet. That was two years ago and the system still blows cold air.

The amount of R134a sounds about right but the short-cycling of the compressor is definitely not right. Jumpering the switch should point to either a bad switch or bad compressor. The tech should have noted that when he did the diagnosis in the first place.

R12 and R134a are different refrigerants so the correct amount of charge by volume or weight will not be the same. A competent A/C tech will fill the system with the correct amount of refrigerant regardless of the type used.

 

the orifice tube and/or screen frequently become clogged with tiny metal chips and if not cleaned or replaced compromises system efficiency. also good to replace dessicator. also good to replace all o-rings. my 93 is 134a and it blows icy cold in the texas heat.

 

It was short cycling with the r12 and the switch not jumpered does not short cycle now withswitch connected..

Is there any way to check the orifice tube filter other thn pulling it? Will it show up on a gauge set as pressures wrong or this tube is not as cold as it should be thing or frosting or lack of it something visual. I am not an ac guy other than to turn it on or off..LOL I work on race cars and bikes only for a living so ac is something I never even bothered tolearn about from day 1.. I could istall a cool suit though know how to do that..LOL..

 

no. but if they were going to do a conversion and you paid and the sob isn't blowing cold, I'd say they didn't live up to their end of the bargain and might demand they remedy it without any further $$ from you.

 

ddahlgren,

Hopefully SunCR will respond as he is very knowledgable with AC, if not quickly, you could do an advanced search for his ID and 'r12' & 'R134' to look up info on the conversion (e.g. I did the search and found a bunch of posts, one mentioned the need to reflash the ECM to change the coolant fan 'on' pressures for R134 to be sooner (vs R12)

However, once question, at what RPM did you perform the test (as per my 94 FSM (R134), it should be 2k)?

 

Mine has a slow leak, a sure sign that it needs another can is when I am idling the compressor short cycles just like you describe.

Picture it this way, the pressure switch designed to save your compressor is on the low side.

You are already low on coolant and then the compressor kicks on "sucking in" what is available on the low side.......this causes the low pressure switch to kill the power......then since you have a closed loop system.....more Freon comes back around and as the pressure equalizes from high side to low side the Low Pressure switch see's the minimum level and returns power to the compressor and the cycle begins all over again.

Have the shop check the levels, or do yourself a favor and go buy a hose with a gauge and can and fill yourself.

The Gauge comes with nifty little colors to tell you when you are safe etc.

90° or more outside when I took this in stop ad go city driving.


It gets down to 45° ish if I am on the highway for a while.

 

I've converted more cars than I can remember to R134, with no performance issues. If they didn't replace the drier and the orifice tube as part of the conversion, they didn't finish the job. Have that done by a competent shop and figure out the cycling switch problem and you should be in good shape.

 

in your estimation, if the orifice tube is clogged, could that be the cause of the lag in the low-side pressure coming up enough in a timely fashion , and that is why the OP is experiencing this "cycling " ?

 

^^that is a good one......I don't know the answer to that and will listen to what Paul says......I like how you put it in post #3

I still lean toward him being low......This is like clockwork for mine...as soon as it get's low it starts to cycle rapidly. I put a can on the hose and hook it up without puncturing the can....just to check...and sure enough the low side is too low....the compressor kicks on and the dial drops to the "low" section.....puncture the can and allow the 134a into the system and the cycling ends within seconds.

Drive on for about 6 months

 

I remember a few years ago with my 87 when it needed a recharge.
I took it to a small shop (no longer in Business) and they checked the temps coming out of the vents which was a warm 66 degrees.
They started to refill the system and I told them to halt! I asked, aren't you suppose to evacuate it first before adding new refrigerent?
Guy gave me a funny look and told him to unhook everything.
Then took it to Midway Muffler & Auto Repair in El Sobrante Ca. where they did the systems check then the recharge and it has worked properly ever since
With a glass roof, there is no way I am going to drive that thing during the Summer months without a good working A/C!

 

^^not exactly true.

If the system has been neglected for years...it may just be a bit low on refrigerant.

So, no, the system does not always need to be evacuated first.

Remember "NOTHING" is a perfect barrier, permeation continues on due to the laws of physics and pressures wanting to equalize. The refrigerant in your closed loop system "IS" leaking and that goes for every single car, refrigerator, whatever.....

Defining "leak"......permeation versus unacceptable leak rate.

So no matter how well your system is working....permeation continues

Now, since the the system never had atmosphere (humidity) allowed into the system....why evacuate first? Especially if you gave the tech the impression that you were not wanting a rebuild.........

 

It depends on how much debris is in the tube. I've seen it cause high lowside and if its really clogged I've seen it cause high highside and low lowside. Sounds to me like whoever did this did a halfassed job.

 

You need the operating pressures (required to be on your receipt in CA for those out here who go to a shop). R134 is 32 degrees at 28 psi so your low side should be somewhere around that number (down to 22.5psi) with the system on high, the main fan running (disconnect the fan switch on the high line), throttle at 1500 rpms, air acrosss the condensor 70 to 85 degrees. The high should maintain a 200 psi average. If the orifice is plugged up, it will show up on the gages. Ditto if it's overcharged/undercharged. Give us the pressures and we'll tell you what it needs.

 

No drier no tube and short cycle was only with the original R12 and lack of charge at least that is their story for all I know the tube was plugged and that is all that was wrong... I called them and they said they would look at it begining of next week. I will ask them to put pressures on the invoice both as car is delivered after their previous work / conversion and new work and delivered back next week.. no pressures no pay that simple. well have to pay to get the car back then a call to visa... If they can not get it right there will be a call to visa anyway as I am not paying 277.00 to have the ac not work.. After I close the shop mabe go throught the checklist in the FSM unless anyone has some real simple visuals. I have to say drove back from a Porshe shop this afternoon in 85 degree heat with no AC for over an hour I was not smiling and not wasting any time on the road either.. LOL

Are the operational pressures the same for R12 and 134 if not should the pressure swithches be changed to ones that run at appropriate pressure for high and low cutout with R134 if different?


Dave

 

R134 is a tad different - it's 32 degrees at 28 psi; R12 at 30 psi. R134 has a smaller molecule; therefore, it's easy to put too much in. R134 also has a tendency to reach extraordinary pressures (300 psi and up) above 95 degrees (and the high pressure switch cuts power to the compressor at 400 psi to keep it from a blowing a hole in the hood). The OEM's keep it under control by turning on the fan(s) sooner. Unfortunately, you can't do that on anything between '84 & '89. The switch that signals the ECM to drive the fan simply opens at about 230 psi - no one makes a switch with a different threshold. You can usually achieve adequate vent temps by doing a couple of things: 1. Reduce the charge to 75/80% of the Factory R12 fill. 2. Lower the threshold of the Low Pressure Switch. For R12, it cuts power to the compressor at 25 psi. For R134, you can reduce that to 22.5 psi. There's an adjustment screw between the terminals and turning it clockwise reduces the cutoff; counter clockwise raises it. The shop should know the drill or they can simply install a new switch which should allready be set for 22.5 psi or R134 (at least the last one I bought was and I didn't bother to check it until my R12 charge started to ice over the lines).

 

I've only perused the original post and responses quickly, but there are several things I will say. First of all it would be helpful to know what year we are talking about.

Them saying that R12 is no longer available is Bu++$#!t. You are always better on these cars staying with R12.

All that said, with some helpful facts from SunCR I was able to get my 134 converted 88 blowing 42 at the vents. The key was charging by weight and NOT overcharging. It has 26 ounces of 134 in it. That is 72% or so of the 2.25 pounds of R12 that is specified as system capacity. When you overcharge you run the high side pressure up straining the system and effect the system performance.

I guess you could put two cans in and then just bleed very small amounts from the third can, but a charging scale makes it very precise and that's how I know EXACTLY how much refrigerant is in the system.

As I said, it's a crying shame that your system was converted. I originally converted mine many years ago when that appeared to be the thing to do. Today I wouldn't convert an original, unmolested R12 system to 134 on a bet. But since you've already gone down that road you have two options to get cold air again and only one of them is a sure thing.

The sure thing is to break all connections, thoroughly flush everything, replace the r/d and put in the correct amount of oil, evacuate and charge with R12. The second option that can probably be made to work correctly is to recover the charge in the system, evacuate and put in 26 ounces if this is a 2.25 pound system(like I said you didn't indicate the year.)

This scenario would not be as sad if it was a DIYer innocently getting into the situation due to ignorance of the subject. What makes it sad is that a supposedly "professional" charged you money to ruin your system.

Good luck with it.

My $0.02,

 

Here is where the current status.. Measured the temp with the hood closed outdoors and called the dealer they could not look at it for a week and it is hot here and wanted the car for the weekend.. Got out the FSM and read the section on ac and the ac controller. Checked that first and no codes... The started it opened the hood to look around and thje compressor is not running with the programmer set to full cold 60 degrees auto and fan at 10 on an 80 degree day. It would every one in a while run but for a very short time and drop out. I pulled the plug off the compressor and there 12 volts and a zero ohm ground coil checks at 3.6 ohm like the FSM is looking for... Pulled the plug for the cycle sw and jumped it system started right up.. Checked the sw and it is 15 ohms.. oops we have a problem gave it a wack and have 3 ohms.. put a new sw on and no runs but does no blow real cold like some have stated here.. After this expense and fiasco I am thinking could have bought a sw a can of r12 and a fill kit be running for under 100 bucks and probably less than that. The charge could not have been real low as I have been using the air and until I discovered the jumpered sw I had no known problem.. After eading the FSM and playing a bit I am thinking I am an accomplished engineer and with a tiny bit of adult supervision I will just do it myself in the future.... I do have a couple of questions though.

1 I am willing to buy a real set of gages as they will last a lifetime no doubt and not break like the typical walmat deal..
2 I will keep my eyes out for a deal on a vacuum pump and up for suggestions there.
3 What do i need in order to recover the charge and not dump it into the open air?
4 I own high quality temp gaging stuff already so good there..
5 I assume there exists either in print the auto ac 101 for dummies around. Lacking that i hope I can ask here and my neighbor is in the appliance biz and has been for 30 years.. so a quick source should I need it as well...
6 What am i missing I don't think I am up for the charging scale unless cheap as I only own 2 cars and going into the ac repair biz..

Dave

 

At this point we need to know the pressures to help you. Gauges aren't too expensive, recovery machines are.

 

if you fix your own system how does everyone else get it done if big bucks for recovery equiptment though think i know the answer..lol