Hi,

I have a 1994 Mazda Protege with a DOHC BP engine. It came with R12 freon but has been converted for years to R134. I replaced the A/C compressor a couple years ago. I put in the oil, pulled a vacuum which was held overnight. I then charged it up until the high side was at about 230lbs on the high side and the sight glass was clear. The low side was good too. I go by the Haynes book mostly when it comes to pressures and such. When I charged it last year, I think, it was about 80F outside which is what Haynes bases their pressures on in the book. I had to catch that one just right. lol

Problem. It cools GREAT when it is not so hot outside. When it gets hot, it eventually blows 60F air after a few miles. It takes a good while to get to 50F. On a hot day like today, it barely got under 50F. If I stop at a red light, the temps go back up pretty quick and the cool down process starts over. Back when I bought the car, it would freeze you to death in just a few miles. I'm talking icicles on the vents cold too.

I live a good 10 mile drive from town. Today, it was about 95 outside, it was blowing just under 50F when I got home. When I pulled into the drive and let it idle for a minute, it was up above 60F again and rising.

My question is, what is the high pressure supposed to be when it is VERY hot outside? I think it is a little bit low but I don't want to put to much in it and blow a gasket or worse, a compressor.

The tipping point is about 92 to 95F when it just seems to start to suck. At night when it is around 85F or less, it cools like crazy. It is cold before I get a mile or two up the road and I have to slow the fan down, or just turn it off a few minutes.

I have a sight glass which looks clear when it is cooler outside but looks a little bubbly when it is really hot outside. That's one reason I think it is just a little bit low.

The Haynes books says for the low side: 22 to 42. High side: 171 to 234. That again is with outside temp at 80F AND WITH R12 NOT R134.

Thoughts on the pressures or anything else?

By the way, the old compressor had a seal failure. I have yet to have a compressor fail mechanically. The shaft seal just seems to get old and leak.

 

How often is the compressor cycling if at all? Is your cooling fan working right? Is the condenser clean, clear and undamaged? Also as I am sure you know you cannot use R12 pressures and weights for a retrofit to R134A, you CAN reuse some components (or all on some cars) but you have to throw out the book when its using R12 numbers, R134a uses LESS refrigerant than R12 so if you used the R12 numbers its OVERCHARGED and will not work correctly, this may be your issue since you could be tripping the high pressure switch and cutting off the compressor but only when its hot. IIRC you need to use 10% less than the R12 quantity when using R134a.

 

When it is hot but not cooling right, it doesn't cycle at all. I can usually feel it or hear the relay click when it cycles. When it is cooler and is cooling as it should, it cycles normally. It gets cold, cycles off, then when the air warms back up a bit, it cycles back on. When working as it should, it cycles off at about 40F and back on at about 45F. It sometimes gets to 38F when on lower fan speeds but about the same as it did when it was new.

Condenser is clean. I clean that and the radiator pretty regular. The condenser fans are blowing fine too. The blower blows fine on the inside too. Actually, I keep my engine clean too. I don't like greasy motors.

I know R12 and R134 is different. I sort of try to adjust it a bit for that when looking at pressures. Thing is, those compressors are made for R12 and the lower pressures. I don't know at what point the compressor would blow a seal/gasket or something. I have looked at different websites but they don't say to not go above a certain pressure or anything. If I knew going above 300lbs would be bad, then I know where to draw the line. Same for 350lbs. Right now, I have no idea how far to let it go. I really don't want to get a new compressor this year.

I found on the internet a A/C website that tells how to compute the ounces of charge from R12 and R134. I think your 10% figure is pretty close. I thought about getting a newer Haynes book to see if it lists my car with R134 since you can't get R12 anymore and have no choice but to use R134. When I bought the current book, R134 was sort of just coming into use. I just hate to buy the book and it not contain any information I don't already have.

I'm pretty sure it is not overcharged. I'm sort of nervous about putting to much so I may not have put enough in it to begin with. It could be that I have a VERY small leak and this heat is making it show up. I usually have to put in a little, half a can or so, every couple years. I have the die in it and the nifty light but I can't find anything. If it leaks, it is a very slow one.

I don't think my system has a overpressure switch. I don't think it has a low pressure either. That is another thing that worries me. If I knew it had a overpressure switch and would protect the compressor, I wouldn't be such a chicken. lol By the way, I have a full set of gauges.

You have any idea how much pressure that compressor can take? I just found this:

http://shbox.com/1/ac_performance_chart.jpg

That look reasonable to you?

 

You may want to check the Dryer. When converting from R12 to R134, dryer replacement is a must. Just a thought. Hope you get it fixed! It is just too hot for the AC not to be cooling to the max.

 

I converted this from R12 many years ago. I want to say it was at least 10 if not 15 years ago. Honestly, I wish I could go back to R12 tho. R134 just isn't as good. A friend of mine puts a little butane or something in his to make it cool good. He claims it doesn't take much either. lol I read somewhere that R402 (?) makes them cold too. If I recall correctly, it only takes a few ounces to really make it cold. Just have to be careful not to add to much.

I just don't like it warming back up that fast when I go to idle. It has always warmed up a little bit but not this much and certainly not as fast as it does now. Something is not quite right.

I'm thinking of pulling it down again, making sure it doesn't have any leaks then charging it back up again. Still not sure tho.

 

Please please please do not do this, there was a time people were using propane as their refrigerant, imagine the mechanics surprise (same with tire changers and fix-a-flat) when something blows up on them due to the gas either leaking out or during recovery.

I would still draw down your refrigerant volume since I still think its overfilled, as for the bubbles I would ignore that since it was also designed for R12 and is now running 134a. Your system uses an expansion valve to control system pressure, if its not working right or if your condenser is plugged up internally it will also give you problems.

Try going starting at 15% under and working your way up (15%->10%->5%) until the output temp starts climbing again to see what your system likes best, also it can help by putting a large fan in front of the radiator as you work to make the conditions more like normal driving ones to test the pressures then as well.

 

If I put any in my car, I'd take it out myself before I took it to any mechanic for service. Putting myself in that situation is one thing but I would not do that to someone else. Plus, I wouldn't want them to recover that and mess up their tank of R134 either.

At one point a few years ago, before the last compressor replacement, I had it charged and it had no bubbles and was nice and cold, even when hot. If I didn't know better, I'd think it had moisture in it, even if just a small amount. Thing is, if I recall correctly, the last time I pulled a vacuum I let it sit for a good while mostly to make sure there were no leaks. Even tho the needle didn't move, I plugged the pump up again and let it run for about 10 more minutes. I can't see how moisture could get in with it under pressure but . . . .

I get my check Friday. I think I'm going to pull it back down and make sure it has no leaks then charge it back up again.

Oh, when I did it last time, I started at a 80% fill compared to what it takes for R12. I think I put just a couple more ounces in it to really get it to cool good and that was about it. Someone else posted 10% less which could be about what I ended up with. I'll likely do the same thing this time but with a little less.

I stopped and did some checking on things. My car holds 1 lb 10 oz of R12 according to the sticker on the hood. That is 26 oz right? When I charged it last time, I put in one can plus a little over half of the last can. I put the last few ounces in my Moms old car. I didn't weigh the can but it felt like about 4 maybe 5 oz. 26 x .8 is just under 21 oz. It should be just about right yet it isn't cooling to good.

This is one of those two sided coins. I see why you would think it is overcharged because in a way, it acts like it is when it is hot outside. On the other hand, it doesn't cool enough so it could be low too.

My plan is to still pull it down and charge it up again. Anyone disagree with one can plus about half of the second to start out with? Friday, it is supposed to be 95F outside. I may get my brother to come down and watch the temp gauge and tell me when it starts to cooling real good. Sort of hard to be in two places at once. Any tips on the high pressures? Everywhere I look seems to say something different. I'm thinking low 200's or so.

While at it, I have one of those large high velocity fans that I put in front of the car about 4 to 5 feet away. It blows air about like a ride down the road at 30 to 40 mph. I stick a screwdriver under the little screw thing on the throttle body to idle it up to between 1500 to 2000 rpms. I try to get as close to 2000 as I can.

I have a new receiver/dryer in the shop still in the box. Think I should replace it too? I got O-rings. I got a large assortment a couple years ago when I caught them on sale. They are sort of green. It's not to hard to get to either.

Anything to add to the plan?

 

Here's a update. I had a friend to call and need a ride out of town. So, I couldn't wait to do something on Friday. I cheated. I took a phillip head screwdriver, a rag and just let out a small amount. This was a 250 mile trip and while it was not super hot, it was SUPER humid. As we all know, humidity is as bad or worse on A/C's. Anyway, it did better. When we came out to leave, I started the car and turned on the A/C. She saw a shoe sale. We all know about women and shoes. lol I left the car running while she ran up to look at and then buy some shoes. The car idled the whole time since I was inside too. When we came back, it had went from steamy hot to blowing about 50F air. Not to bad. It had cooled the car a lot. You just have to be there to grasp the job it did in those few minutes.

I took her home and while there, I let out a little bit more. It got even better. Over the past couple weeks, I have been letting out small amounts hoping for that sweet spot. I'm about there. It still does good going down the road but does pretty darn good even while idling.

I'm still confused about something tho. I put a rebuilt compressor in the car about 3 seasons ago. It was in the spring time I remember that for sure since the compressor actually went out in the winter time. Anyway, it ran all that summer, last summer then this summer it was overcharged. If it ran two seasons like it should, how come it magically got overcharged this year? No one else drives my car. Nobody else works on it either. There is no way someone put some in without me knowing about it. Also, I got a nice alarm on that puppy. It would go off if the car is even touched much less raising the hood and working on something.

Can someone make sense of how all of a sudden it has to much juice in it?

Thanks much for the help. I would have never guessed it was overcharged for sure.