The Red Cabrio Barn Find Project

[jeffnhiscars]

There aren't really any pics to add at this point since there is nothing new in pulling a vac and charging the system so from here on, its pure art & science. After filling the pump with oil and connecting it via the yellow hose it spat out a healthy wisp of white smoke within the first few seconds. The gauge also shot to -30 just as quickly. Obviously this did not meet the standard for "deep vacuum" so I let it run for an hour then turned it off.

The big question at this stage was if it would hold the vacuum so I let it sit for another hour..and damn if the gauge did not move. Thank you Nylog Blue !!

The 2 main ways to charge are by weight and pressure. Pressure requires way more finesse as the variables are ambient temp, humidity, compressor speed and I will get to more on this later. Weight is weight, so I pulled out my digital scale again. The full cans weigh exactly 1 lb (454.4 grams) and hold 12 oz of refrigerant. Add 90.3 grams for the valve since I knew that last partial can would have to be weighed with it. BMW calls for 900g of r134a +/- 25g. Basically, 31.5 ounces which is bang on the often quoted 10% reduction from the 35oz r12 charge. Keep in mind that these specs are for a converted system using the stock compressor which has either had the seals swapped or was installed w r134a compatible seals. Either way, those compressors were designed to run on r12. more on that later.

I found at that its best to not to fully open the valve on the can as it will freeze even when you set it in a bowl of fairly warm water. Patience was the order of the day. I went through 925g of refrigerant and given that I burped the gauge end of the yellow hose every time I changed cans to clear out any air, I figured I was right where I needed to be. When the pressure in the system equaled can pressure I started the car so it would pull in the rest and the good news at this point is that the compressor engaged and the gauges noticed.

[jeffnhiscars]

Now Im ready to evaluate the system. By design this should be state of the art with the only limiting factor being the size of the evaporator which is just not open to debate. Hitech compressor, PF condensor, Spal pusher, new evaporator & e3xpansion valve...this is a no brainer. I even put on a tight tshirt since I fully expected to take pics of my nipples turning in to pencil erasers...this was exciting lol.

Strangely, the air coming out of the dash vents was not all that cool. After a brief survey and not finding anything amiss I decided to take it for a drive. What I realized was, that while my slide controls were set correctly, all the individual vents were shut off...duhh !!

As soon as I opened them it got instantly comfortable in the car but it still didnt feel that cold. I knew the risks of over charging and since it was working passably I gave it a few days. Next look I checked the sight glass and saw some frothing in there which told me I was undercharged despite having used the recommended amount, so I added another 3-4oz's. The sight glass cleaned up and the vent temps came down marginally.

So now Im driving around with my BMW ambient temp/humidity/vent temp chart and my infrared gun checking the vents on all kinds of situations. The key measure for me was the temp differential between what my OBC gave for outside and the vents all the while trying to factor in the effect of humidity as per the chart. Some examples..

at 60% and 80 degrees BMW says the vents should be at 53 for a 27 degree spread
at 70% and 80 the spread drops to 24 and at 90 degrees it drops to 23
Now at 80% humidity and 90degree outside temp the diffential drops to 21, which means they are saying 69 degrees at the vent is on spec.

Im close to these vent readings but think Im a bit higher although I am extremely comfortable from the minute I get in the car. My business partner has a 2010 135i Cabrio and frankly his AC sucks. You put it on max and by the time you get to the restaurant you are sweating. No such issue in mine.

What I do know is that humidity is every bit as critical to comfort as temperature and depending on where you live many central AC systems are regulated by a humidistat as well as a thermostat. My theory then, is that my system is doing an amazing job of pulling the humidity down from obscenely high levels (its in the 80-90% range today). This is supported by the large runoff under the car when I park. True the drains may be slow but Im not so sure.

The other factor to consider is why humidity effects system performance as much as it does and the simple answer (if there really ever is one) is that when vapor condenses, which is does in the evaporator (seems silly when there is an actual part called a condensor) it throws off a ton of btu's which come right out your dash vent.

The science is simple..apply heat to water it turns to vapor. Take heat out it condenses. If that happens inside the passenger compartment your vent temps go up.

Now my AWII Cabrio is converted and it has vent temps of 37 degrees. It also has the stock compressor and the gauge pressures are a fraction of what they are in the Seltec system. Why it gets this cold I cant say but the system was designed for r12 head pressures and honestly that car is not nearly as comfortable as the barn find despite its chilling air flow.

What occurs to me is that perhaps the new evaporator has improved air flow and heat transfer which provides for better dehumidification and thus more comfort even at slightly higher temps.

For now Im putting the infrared gun away and will revisit this when the humidity levels are more normal. Bottom line is the system does what it is intended to do as well as any AC system I can recall and at lower fan settings (ie 2 or 3 not 4). The other factor is that being a pure r134a designed compressor, the higher operating pressures probably demand a higher refrigerant charge to hit the sweet spot. I think Im close but may yet add a bit more in time. There really are no reliable specs if you upgrade the compressor. Thats the art part

[bradnic]

DAMN Jeff. this is tiiiggggghhhht... Haven't been here for a while but glad to see this project moving forward!

My vert's euro MT1 conversion has been on standby since I've been working my son's cars this summer, a 318is and 325ix both getting engine and suspension rebuilds + new A/C. will definitely keep an eye on your progress

[jeffnhiscars]

Thanks Brad.

Ive actually had some doubts about the AC since I have not been getting the temp differential I expect but this outrageous humidity has made it tougher to set standards. I did find a slight leak at the HP switch so I tightened that down and seem to have stopped it. Today I was getting a 27 degree spread which is more than adequate but Im still not convinced Im optimized.

If anything is less than perfect I'm leaning towards a sticky expansion valve since there really arent any other suspects and being new OE does not guarantee its perfect. I have noticed that after a good run at highway speeds I hear what sounds like a cricket chirping under the dash and wonder if expansion valves can chatter.

I also discovered that my temp dial only turns clockwise to about 3 oclock. I pulled out my spare HVAC unit and you can see the flap clearly enough. It will go down for max cool but on the way up for max heat its either binding against the evaporator or the lever behind the air outlet is jammed on something. Im not quite sure why/how its doing that but I guess I have til November to really worry about it :-)


I also decided to tackle the coolant trickle under my tstat housing. I was fairly sure it was either the fitting to the TB hose or the housing itself since I did do some JB repairs on it when I swapped in the head. I found this and had spares so consider myself lucky.


Speaking of November....


Plus a few spare widgets

[lolcantturn]

That AC write up is incredible.

[cory58]

I met Jeff this weekend when he parked his project car next to my '92 vert. He's a great guy - didn't mind answering my E30 questions for 45 minutes.

The engine compartment of his car is immaculate. It made my car look like the "barn find" under the hood.

Cory

[jeffnhiscars]

I met Jeff this weekend when he parked his project car next to my '92 vert. He's a great guy - didn't mind answering my E30 questions for 45 minutes.

The engine compartment of his car is immaculate. It made my car look like the "barn find" under the hood.

Cory

Hey Corey. That's was an awesome encounter with another e30 addict.

I was picking up a pair of shoes in for repair and I parked next to another red e30 Cabrio. I was looking around for the owner and there's Corey grabbing some white shoe polish (yes I noticed). Well we looked at each other and almost in unison said "is that your e30" lol.

He had left his polish in the counter and when the shop closed the owner handed him his polish on the sidewalk while we kept gabbing

THIS is what I love about this community :)

[Bimmer_man]

damn i bet its like a damn blizzard in that car now. While all of us are burning to death in this heat hes got a coat on with some coffee. Subbed cant wait to see whats next.

[cory58]

Hey Corey. That's was an awesome encounter with another e30 addict.

I was picking up a pair of shoes in for repair and I parked next to another red e30 Cabrio. I was looking around for the owner and there's Corey grabbing some white shoe polish (yes I noticed). Well we looked at each other and almost in unison said "is that your e30" lol.

He had left his polish in the counter and when the shop closed the owner handed him his polish on the sidewalk while we kept gabbing

THIS is what I love about this community :)

Yep - I'll definitely be stopping back by to pay for the shoe polish, and repaying the owner's generosity with some resole business.

Only one correction - the polish was "nuetral". My wife would confirm that I'm definitely not stylish enough to wear any white shoes that aren't tennis/running shoes!

Take care,

Cory

[88e30vert]

Just read through the entire thread and this should be a sticky for all e30 verts. I would like to get my a/c working but my condensor fan is seized up. The OE fan cost $260, is it worth going the spal fan and harness route or just bite the bullet and buy OE.

Sent from my LG-P999 using Tapatalk 2

[TrentW]

I like this thread a lot.

I really do.

[jeffnhiscars]

Just read through the entire thread and this should be a sticky for all e30 verts. I would like to get my a/c working but my condensor fan is seized up. The OE fan cost $260, is it worth going the spal fan and harness route or just bite the bullet and buy OE.

Sent from my LG-P999 using Tapatalk 2

I dont know the cfm rating on the OE fan but I do know its noisy as hell compared to the Spal which, even in Canada should be quite a bit cheaper than the OE.

If you want a used one mine works fine. You would just need to replace the plug which I cut off to make my new harness. PM me if you are interested.

[jeffnhiscars]

If you don't fall asleep while reading this then keep in mind a couple of key points...HVAC systems do not create cold but rather they only relocate btu's and they need to do so faster than the space they are conditioning can regain them (this is your "heat loss").

If you have a heat pump in your house it's really just a refrigerator that changes direction in the winter, moving btu's from outside to inside. Due to efficiently limits they do not work very well once you get close to freezing since there are no longer enough btu's in the outside air for the system to warm the inside of the house so you have an auxiliary plenum heater. Below freezing heat pumps are not the best choice.

Because the AC system in your house is on recirculate 100% and is way better insulated than our cars the typical temp differential between what comes out of your vents and what goes in to your returns is on the order of 17-20 degrees. This assumes the house that is not leaking like a sieve and the system design calculations to insure enough capacity are very well established.

Now humidity is as important to comfort as temperature. I had a 5 car garage that I converted to a duplex and yes, today I would KILL for that garage, but at the time it was the right thing to do. The plan was to have a 1 br suite and a 2 with one of those BRs being an office which was insulated for sound proofing and only to be used so many hours/day...so basically 3 separate spaces with very different HVAC needs. I looked in to zoning them out with VAV vents (variable air volume) like the ones used in office buildings and just having one system. The problem would have been that when that office called for AC it would have cooled so quickly with the larger system that it would have cycled too quickly to remove enough humidity to make it comfortable so you wind up setting the tstat to a much lower temp to extend its duty cycle/run time. Not good design.

Now we move to our cars. Remember there are 2 ways to gain heat in a car you are trying to cool. One is through radiation through the shell and glass, the other is air leaks. A hardtop is actually fairly tight (or should be) so given its small volume, leaks are not a big deal, but if you have torn door seals, fix them. Cabrios are another story. They are sieves with cloth tops that do not keep heat in our out so your AC system has to work especially well.

The other major difference between a house and car AC is that your car does NOT cycle and is designed to draw in fresh air 98% of the time which demands a much higher temp differential than a house. Of course we put it on recirc for those first few minutes to minimize warmer fresh air and the real enemy... more humidity. Unfortunately, since humans exhale even while driving you really cant go for too long on recirc before it gets unpleasant. It amazes me how often I get in to someone elses car and they have it on recirc all the time. Its the first thing I change after a do up my seat belt (second is usually the stereo :-)

Another side of humidity is in places that have very damp climates such as the PNW. I ran my AC in the winter with the tstat set to warm. If you look at the pic I posted of the inside of the AC unit, you will see that all air coming in the cowl vents goes through the evaporator, but when you are in cooling mode, you divert air so it does not go through the heater core. When you set it to heat the air goes through both, so if you hit your snowflake in winter you will get hot dry air. Not only does this make it more comfortable but its what you do when your windows fog in winter regardless of outside temp.

I'm rambling. Sorry :-)

[E30nub1]

you will get hot dry air. Not only does this make it more comfortable but its what you do when your windows fog in winter regardless of outside temp.

I'm rambling. Sorry :-)

Mind blown...

[jeffnhiscars]

Now, to hopefully give some meaning to all that bullshit, let's take another look at what my car is doing.

I have 2 baselines for how well the new AC system is working. One is the temp differential (lets call it TD) between the infrared reading at the vents and the OBC outside temp. I check these constantly and I do ignore readings until I have driven for a few minutes since the ducts heat up when parked and we know the OBC reads hotter than the outside air from sitting in a parking lot. The second one is humidity vs my comfort level. Im trying to be somewhat scientific :-)

Until I stopped that leak at the dryer and topped up the charge i was getting TDs in the high teens low 20's. Typically on an 85 degree day my vents would be mid 60's when the humidity was 65-80%. Tolerable and better than sweating but really not that great although that is actually not far from BMW spec at that humidity. I also noticed that after a few minutes on the highway I would sometimes get much greater TDs but only briefly. I chalked that up to passing through an area of lower humidity.

After a week with the leak fixed I am getting very different results. I left the office one day and had OBC readings in the mid 90's. Its a couple of slow blocks to the main road and due to the time of day I had to sit there for 10 minutes before I could turn on to the interstate so there was really no oppty to get the compressor or vehicle speed up or for a rapid cool down period. It was not horrible which, given the circumstances, I would say was great.

In general, my TD is closer to 30 and one day when the humidity was finally down around 50% and the OBC was mid 80s I was getting TD's in the high 30's and once even hit 40 (so 44 at the vent). I mostly run with the fan on 2 and could not ask to be more comfortable despite the canvas top.

I'm sure Ill get static for this but Im going to say that R12 is NOT better than R134a. BMW's conversion bulletin shows almost identical vent temps in various temp\humidity ranges with both refrigerants but this is for r12 designed systems. The pressures differ quite a bit which we know. The problem is, that an r12 compressor is not designed to run at those pressures or to be as efficient with r134a as a compressor designed and build for that purpose. We also have no long term reliability data for r12 compressors running at r134a pressures (other than being poor) so I'll add that fly to the cost\benefit ointment

So yes, if your OE compressor seals are rated for conversion and it still works it makes sense to try to use it...my AWII cabrio is an example...but if you are replacing your compressor it makes zero sense to find an OE that is conversion rated. New or remans are stupid expensive and used ones are mainly useless. Lots of stories of good results from converting using bailing wire and deep fryer oil but I paid $195 for the Seltec and $150 for the mounting kit. Go buy a Behr or Bosch for that.

My 2c then is r134a in an r12 system can work but r134a in an r134a system will work better and is more serviceable.