calpatriot

Does anyone know where there are manuals/specs for the S4 dealer-installed AC system? I am working over the system in my 86, and there is virtually nothing in the FSM. The Haynes AC book has a few cryptic numbers (14 lbs on the low side, 225-275 on the high), but nothing on what the system should be with R134a (mine is converted).

Also: how to get/connect nitrogen under pressure to check the system for leaks?

j9fd3s

iTrader: (3)

they didnt have r134 when the manual was printed.

pistones

iTrader: (5)

i hope you know those numbers mean pressure not refrigerant weight.

scrip7

iTrader: (6)

The pressure range for 134a is wide depending on a few factors. It is easy to over-charge the system in hopes of making colder air. The stock serpentine condenser in our 7s is grossly inadequate in capacity for retrofitting to 134a. It can be done, albeit with lackluster results. With an ambient temp of, say, 95f, and engine at 2000 rpm you should see no less than 200 psi and no more than 275 high side, and no less than 20 psi and no more than 50 psi on the low side. The lower the pressure on the low side the better the cooling, but to an extent. A lot depends on the condition of your compressor, how much airflow you have across the condenser (e-fan, stock fan and clutch, shroud or no shroud, etc). As for leak testing, I use a green fluorescent dye at my shop and a black light to find leaks. The dye can be found at most parts stores.

calpatriot

scrip7

Thanks for the very helpful reply.

I am showing 20 & 200 psi at last check, but since then I have replaced the blower and the airflow is perhaps 10x what it was before, and it seems to have helped the performance. The other day I was showing 58deg F at the center vent, with the inlet on outside air at about 95-97F.

I have replaced the receiver-dryer and the expansion valve, but on evacuating the system I was unable to pull vacuum below 14"Hg. However, when I stopped the pump and closed the valves, the system held that vacuum overnight with no reduction in the reading (i.e. it was still 14" in the morning.)

I have UV dye in the system, and I am going through the process of cleaning off all of it that I got onto the fittings during the rework (did a pressure wash with degreaser yesterday). There seems to be evidence of a small leak (under the black light) around the front top of the compressor, apparently on the compressor case about 1" behind the pulley. So far I have found no other leaks. Is this likely to be the source of the inability to pull a better vacuum?

You indicate that the stock condenser is inadequate. Are the aftermarket condensers better, or are they simply a reproduction of the same inadequate design of the original? I notice that Kragen Auto Parts has a condenser for my RX7. It is $175, which I am willing to spend if it is an improvement, but not if I am replacing like for like.

The Haynes manual says the low side pressure should be 14 psi. I have charged it to 20 psi, but at that level I tend to get high side pressures less than 200 psi. I don't tend to get high side pressures in the specified range (225-275) until the low side gets into the range of 35-55 psi. Is that normal for R134, or (as some of the literature indicates) is that an indication that I need to replace the compressor?

Thanks,

scrip7

iTrader: (6)

If you are able to pull 29" of vacuum when not connected to the car but only 14" when connected, then yes you have a leak. Sounds like the compressor case seal at least. The haynes manual spec of 14" is likely for R12. If you were to have a low side reading that low with 134a, and perhaps a high side of 200+, I would suspect a high side restriction, which isn't your case. You stated you could get it to run pressures of 225+ and 35-55 which would be the normal range for 134a. As for the condenser, make sure it's a parallel-flow design rather than a serpentine-type. Makes a huge difference. This is the site I recommend getting your condenser from. I use the CN-21003C at the bottom of the page. It has the fittings on opposite ends making it a little easier to connect up:

http://www.polarbearinc.com/PBPC/hom.../CN/CN_PF.html

You will need to have an a/c shop weld up a tube on the passenger side to connect to the dryer, but it's not as big a deal as it sounds and not expensive. This is a triple-pass condenser, and you will be amazed at how cold the center vent temp will get.

calpatriot

That's the way I see it (must be a leak), but what gives with the fact that it seems to hold the 14" vacuum indefinitely with the pump disconnected? Seems to me the vacuum should decrease over time...

I picked up an electronic leak checker today. On my first go around with it, the only place I was able to get it to go off was at the top front of the compressor, just behind the pulley. I will play with that more some tomorrow.

When you do the new condenser, do you just bring them the old condenser to weld a similar pipe, or is it better to bring them the whole car with the condenser installed?

Thanks,

scrip7

iTrader: (6)

The vacuum pump you're using may only be capable of a 14" pull, that's why I asked what the reading would be without the gauges connected to the car. The gauge hoses or fittings may be leaking, not allowing a 29" pull. It's easier to just take the car to someone that can weld up the tubing with the new condenser installed. The local a/c shop I took the car to did it all in the same day. You can put your leak detector tip in front of the center dash vent and then turn the blower on low speed to check for evap core leaks. That method works best if you check it with the system fully charged and after about 15 minutes after you shut the a/c off. This allows the refrigerant to build up in the evap case and be detected when you turn the blower back on.

calpatriot

Thanks.

The pump is the one from Harbor Freight, brand new, and supposed to be capable of pulling to within 0.004" of a pure vacuum, which it seems to do as soon as I unscrew the ***** for the pins which open the schraeder valves on the car. With the quick connectors still on the car, but the schraeder valves closed, it goes to well over 29" in less than a second.

So far I have been unable to find any leaks except the one near the top front of the compressor with either the UV or the electronic detector.

As I understand, the system pressures with R134a should be higher than R12. The book values (Haynes) for this system are 14 and 225-275. I can't get the high side values up into the 250 range unless I charge it enough that the low side readings are up in the 50 area or higher. I have replaced the expansion valve and the receiver dryer.

My reading indicates that the high pressure on the low side, combined with the low pressure on the high side, indicates a weak compressor. That would perhaps be consistent with the small leak I am detecting at the front of the compressor. Am I on the right track?

How much higher should the high side reading be on R134a vs. R12? The original specs are all for R12. If it should be 10% higher, that would correspond to 275 psi +/- 25.

I was reading a manufacturer's site on the expansion valves. Two things caught my attention: the expansion valves are set up for the working refrigerant. They say that the bulb is charged with refigerant, usually the same as the one the valve is intended to control. Do I need a different expansion valve for R134a? Also, they indicate that the sensing bulb should be located not at the bottom of the evap output pipe, but located between 1 and 4 o'clock around its circumference, depending on the pipe diameter, which they do not specify. Mine is at 6 o'clock (directly underneath the pipe) because thats where I remember the original one being before I took it out. The company says that the oil pooling in the bottom of the pipe can cause errouneous temp readings and change the valve performance. Should I go back in and move the bulb to a position other than the bottom of the pipe?

I looked at the high-efficiency condensers on the site you recommended. I think I will upgrade to that when I change the compressor (not this week, I have busted my car upgrading budget for the near term).

There was an electric fan in front of the condenser on the automatic transmission cars. I was thinking of adding one of those at the same time. What do you think of the fan idea, and what about the factory fan vs. aftermarket? I have a couple of aftermarket 12v fans laying around the garage, left over from a previous project. I might could adapt those, or do you think the factory fan is a better idea?

Thanks,

scrip7

iTrader: (6)

You're on the right track with the compressor. The closer you get to the 50-60 PSI range on the low side in order to get the high side in the 250-275 range, the weaker the compressor. I have seen many makes and models of cars with worn out compressors with a low side of say 55 and the high side at perhaps 150. At that point, adding more refrigerant only made the low side pressure go up. And compressors with the most wear are nearly equal in pressure on high and low side.

The expansion valve isn't as much of a contributor to the 134a conversion as is the condenser, but there is a difference between r12 and 134a valves. The molecules are smaller in 134a than r12, so the orifice obviously needs to be smaller to produce the pressure drop required for liquid state/vapor state to take place. In my Vert Resto thread you can see where I replaced my expansion valve with one rated for 134a. If I remember correctly, I bought mine from O'Reilly so you might check online for that.

On my NA car I used a TII stock fan and shared the power source with the compressor relay, which has contacts that are heavy duty enough to run both for quite a while.

jackhild59

iTrader: (7)

Ok, here is your main obstacle. If you have a leak, you are pulling air into the system with the vacuum. When you have air in the system, you are never going to make a good functioning cooling system. Until this leak is solved, you will never get pressures that make any sense. You are also damaging the capacity of the new drier by pulling in air/humidity.

So fix that leak first. If it's in the compressor, replace it. FourSeason's remans have a bad rep with the professional trade, yet they are the most commonly available to the diy market. They call them 'For Seizen's' due to the tendency to fail catastrophically. You would be better to find used a low mileage OEM compressor from the FS section of this forum.

Temperature and pressure are directly proportional in relationship. Here is a pressure-temperature chart for each refrigerant. http://www.aircondition.com/pressure.htm This will help you relate the differences between the two refrigerants. Pressures when the system is operating will still not make perfect sense until you are at the point of understanding both superheat and subcooling.

Regarding the TXV-yes, in a perfect sense the TXV should be replaced with a 134a valve, but that is really the very,very least of your issues. You can actually make more difference in performance by adjusting the location of the sensing bulb than the difference between R12 and R134a TXV . If you have it at 6 o'clock, move it to 5 o'clock or even 4 o'clock. If you move it too high, you will have evaporator freeze-ups. If you have adequate condenser area (parallel flow condenser) and sufficient airflow (verified oem fan clutch) across the condenser, that TXV difference won't matter much.

Here is why: When you look at the T/P chart you will find that the pressure difference at a 35*f evaporator temperature is only 2.2 psi. Since expansion valves are adjusted to a temperature based on the refrigerant in the bulb, the R12 valve will be trying to keep 35* but the R134a will be passing at a pressure that will yield 37*. The valve will therefore 'hunt' between 35* and 37*-no big deal . The difference in refrigerant molecule size is really a question about refrigerant capacity. And capacity is not an issue since TXV's are sized 1.5-2.5 times higher than the pumping capacity of the system. This allows the valve to slam wide open and 'keep up' during initial cool down when there may not be a completely solid column of liquid refrigerant from the condenser to the evaporator. TXV is not expensive to replace, so the choice is up to you. Personally, I wouldn't bother, especially since you have a brand new one for R12 on the car.

Also, I see no mention of your oil charge. This is important for a long lasting trouble free system. In a system that has had R12 ONLY use Ester oil-NOT PAG. PAG and any R12 Residue/mineral oil residue etc. turns to bad nasty goo. Stay with Ester since it is compatible with the new and the old refrigerants, oils and any residues.

When you change refrigerants, the old used or the new compressor should be flushed with the new oil. A brand new compressor may come in dry. Flush the compressor before install by adding 2-4 oz of oil fresh ester oil, hand-turning the shaft 10-15 rotations, then dump the oil. Repeat 2-3 more times if the compressor is old/used. Once is probably enough if it is new and dry. If it is new and comes in with PAG, flush it like it is a used compressor. After flushing, add 3 oz of ester to the compressor. Add another 3 oz to the drier. This is the entire oil charge necessary split between those two locations.

I like Scrip7's idea of the condenser fan operating with the compressor.. Oem or aftermarket doesn't matter but I think the OEM will be more durable in the long run. I would probably add an additional OEM sealed relay for the fan only.

Good Luck!

calpatriot

OK, I'm looking at the Kragen/O'Reilly site, and there are several different expansion valves for the RX7 (half for the factory air, half for the dealer installed air, like mine). Not a one specifies that it is calibrated for R134... those that I have found on the internet that state the refrigerants they are compatible with specify *both* R12 and R134. Marketing?

I will move the sensing bulb to a higher position when I open the system the next time. At least one reference I found said it should be as high as 1 o'clock, depending on tube size. ???

I found the sanden compressor service manual online as a downloadable pdf. It says any compressor that can be forced to pump out 350 psi is good. Hmmm... I suppose they meant to say also "...on a normal charge"?

I notice that the last digit is the displacement of the compressor (some references say in cc's x 10, others say in cubic inches. In any case, if R134 is 30% less effective than R12, would it not make sense to upgrade to a larger compressor, such as the -13 or -15? Has anyone done that? Would they fit? Is this a non-issue if the system is condenser-limited?

calpatriot

Sanden compressor service manual is at...

http://www.sanden.com/images/SD_Service_Guide_Rev.2.pdf