Economical AC Repair

[ZCAT3]

O.K. - as some of you may have read I recently spent big dollars to repair and upgrade the AC system in my 86 930. I spent north of $1000 buying parts from Performance Aire (new barrier hoses, receiver/drier, belly condenser, bulk head vent, etc.) and I did all the work myself. The result was an AC system that kicks but for a 911 - vent temps in the lower 30 degree range - but my was it pricey.

I also have an 87 Carrera that is a daily driver / DE car. The AC in that car was DOA as well so I decided to go the least expensive, yet correct way to repair this system. I pulled my hoses and sent them to http://www.ACKits.com in Arizona to have new barrier hoses made. ACKits also sent me a new receiver/drier, new O-rings (with tons of extras), and some other various parts thrown in for good measure (extra clamps, zip ties, etc.). The receiver/drier they sent me and charged $17.80 for was the same model that other "Porsche" AC shops sell for well over $100. I installed the new hoses and receiver/drier and charged the system today. We are getting upper 40 degree vent temps (which is what you expect from a healthy stock 911 AC system). The total damage for all new hoses and fittings, the receiver/drier and the other goodies mentioned above was $134.

[fogcity]

Thanks for info.

[nhromyak]

Curious why you went with barrier hoses?

Are you still running R12?

As I understand a true R134a system does not leak past non-barrier hoses. Only R12, and R22 leak past the non-barriers.

Did you do any other mods? Such as TXV replacement?

Upgraded parrallel flow condensor, other condensor?

Compressor upgrade/repair?

Thanks.

I have been working with R12a. As I have not wanted to R&R the oil and drier. But it looks like I need to atleast Flush my system. I may also need a compressor. Not sure on this yet, because of the nature of R12a.

I THINK, for R12a to work better (along with R134a) the TXV's superheat needs to be adjusted down. Unfortuntaly, and as far as anyone can tell me the TXVs on my '85 are not adjustable.

Thanks again.

[ChrisBennet]

I thought 134a had smaller molecules and leaked faster than R12?
-Chris

[nhromyak]

That's what I thought too...

I also thought R134a is a mixed refrigerant like R12, and it loses it's affectiveness when it leaks out. But that is not the case either!

I was initially told differently from www.ackits.com forum.

Then I doubled checked with the EPA.

AND Not according to the EPA either.

The funniest thing I found is that the EPA also recognizes R-12 and R134a (albeit at different rates) as an OZONE depleting refrigerant!!! So why is it legal for DIY-ers I don't understand.

As it was for R12, it is illegal to "Vent" R-134a in the atmosphere.

If you do, or plan to convert to BARRIER type hoses (for R12), you MUST have a high pressure cut-off switch. This way you don't blow-out the hoses.

This biggest problem I read and hear about is how converting to R134a was not done correctly, and people (not just porsche people) are losing there compressors. The system MUST be flushed COMPLETELY! A new Drier, and filters as appropriate, clean and flush the compressor for new oil.

Now R134a will kewl slightly less than R12. BUT there are ways to make R134a work better, such as an adjustable TXV (expansion valve), and/or more condensor, or more efficient condensors (parrallel flow). Usually an evaporator upgrade, and vent upgrades will help as well.

Good luck.

[ZCAT3]

Nick - yes, this is with R-12. In a nicely selaed system, the R-12 charge should last everal years.

I do not think you can get anything but barrier hose these days. Porsche is one of the only car makers I know if that used the non-barrier hose. In any case, my hoses were severely damaged and had to be replaced. The deck lid had virtually rubbed through one of the hoses and a past owner had fixed the underbody hoses with metal pipes and hose clamps. I doubt it would have held any pressure at all. The compressor had been replaced maybe 7 years ago with the newer Seiko rotary style from Performance Aire. The receiver/drier should always be changed when a system has not been used in a while. My car still had the original unit in it. For $18 this was a no brainer. I am told that the expansion valves and evaporators should not go bad on these systems (although they obviously do in some cases). If I were you I would do what I did as a start and fire up the system. That way you can see if the compressor and other component work. ACKits also sells the NipponDenso compressor for these cars for somewhere in the $300 and expansion valves for $25. The NipponDenso compressor is what is on my 930 and it works great (I am still using the original unit from 1986). The only noticeable difference is that when the rotary compressor cycles on and off it barely affects the engine at all, whereas the older style NipponDenso compressor does suck some power (particularly noticeable at idle).

Adding an underbelly condenser is a great upgrade - probably the best thing you can do to get better cooling. I am thinking about trying to add a small fan to the rear lid condenser as this should help quite a bit as well.

[RickM]

Couple of questions:

-Where would one position the underbelly condenser?
-Why was it necessary to send the old hoses? Were they not off-the-shelf? Or were components from the originals used?

[ZCAT3]

Rick - the under belly condenser mounts unde rthe front passenger footwell. You can see it at www.scottsind.com and also can search this BBS for Jack Olsen's pictures. On the hoses, they were custom made, not off-the-shelf, and I thought I could save a few dollars if they could reuse the fittings. They gave me all new fittings anyway, but did need to use the bracket for the passenger side rear condenser mount (they welded it onto a new fitting). One note, I would have the shop add a few inches to each hose as if they hoses match the original length like mine did it is a tight fit. It appears that the original hoses were run before a lot of parts were on the car, like the brake lines, and in some spots you have to route over places the hoses went under before. A few inches here and there would have helped.

[ChrisBennet]

How much does an underbelly condenser run?
-Chris

[RickM]

Not sure what the cost of the Scotts condensers are but I would seriously consider upgrading to a parallel unit from ACKits.com

http://www.ackits.com/index.cfm?fuseaction=Parallel

[ZCAT3]

Maybe I should have done that - do they make one that will replace the rear deck lid condenser?

As an aside, does anyone know what makes a compressor run hot and/or have high pressure on the high side and low pressure on the low side?

[ruf-porsche]

Originally posted by ZCAT3
Maybe I should have done that - do they make one that will replace the rear deck lid condenser?

As an aside, does anyone know what makes a compressor run hot and/or have high pressure on the high side and low pressure on the low side?

The compressor compress the refrigerant that is why the pressure is high (Duh is that why they call it a compressor?) and for the same reason when the compressor draws the refrigerant from the evaporator it creates a suction so the pressure is low.

The change of refrigerant from a liquid to a gas and back to a liquid is why we can enjoy our ac (at least those with ac that works).

[ZCAT3]

O.K. - I am not that dumb - the pressures should be 120 - 200 PSI on the high side and maybe 20 - 30 PSI on the low side. I was seeing over 300 PSI on the high side and maybe 15 PSI on the low side.

[Adman]

ZCAT 3....Kudos for taking the time to shop the components you needed. I just rolled over and payed $1,800 for PA parts. List included, barrier hoses,underbelly condensor,Seiki-Seiko Rotary compresser, vent modification kit and dryer. It then cost $225 to evacuate, pressure test and recharge with R-12. At the time I felt like I must have been insane to spend that kind of money and provide all the labor. The 106F+ heat index we have in Houston made it all worth it. I have left the car purposely baking in the summer heat for a couple of hours just to see how long it would take to be confortable once running. Takes about 15 minutes to reach the comfortable point and the vent thermometer was reading 130F when I got in the car. Thats respectable. As you have pointed out there is a great deal of money to be saved if you package the parts for the project yourself. So many on the forum have done it but I have never seen a complete mat'l take-off for the hose, lengths and fittings. Something you could just hand a supplier and have made. I probably paid 3x what the hoses were worth. To my knowlede no one has been able to source the exact under belly condensor and if you havent seen it in person you wouldnt know what level of durability to pursue. Well got off on a tangent here. What were we talking about?
Matthew

[sammyg2]

OK, layman's explanation of an AC system, without all the technical lingo like evaporator, condensor, yada yada:

The compressor just pushes the refrigerant. the pressure differential is actually cased by a tight spot in the line (orifice or expansion valve).
The compressor pushes the stuff hard enough to increase the pressure. this as we all know from studying boyle's law causes the product to increase in temperature. it is sent through a radiator where the extra heat is transfered to the surrounding air. The product, now much cooler, then goes through the orifice and expands quite a bit causing a large drop in temperature and it gets cold (boyle's law again).
It is passed through another radiator where ambient air is cooled as it is blown past the outside of this radiator. That cooler air is sent into the car and you get cooled off.
The refrigerqant is now warmer after it absorbed the latent heat from the air that cooled your bod, and it get's sucked back into the compressor to start the cycle again. All an AC system really does is move heat (energy) from one place to another i.e. from inside the car to the outside of the car.

ZCAT3, in regards to your question, higher pressure on the high pressure side along with higher temperatures, just means you compressor is compressing more than normal. It could be because the compressor is much more efficient or because the expansion valve is partially clogged or improperly sized, or maybe a hose is kinked?
If the refrigerant being compressed is thicker than the old stuff that would give you the same result. The expansion valve needs to be properly sized for the system, including the type of refrigerant.
So in conclusion, I really don't know

[Adman]

I think I understand now. I thought it was like Magic or something! Well explained keeping it simple.
Matthew

[ZCAT3]

Thanks Sammy - I understand the basic idea of PV=NRT or whatever the equation is. I am using an upgraded Seiki-Seiko rotary compressor from Performance Aire and the rest of the stock parts. Hopefully the expansion valve is the right size (unless it was changed along the way), but I do wonder if the hoses are kinking somewhere. I was told that unless a hose is severely kinked, the system pressure will have no problems. The long hose from the rear condenser to the front condenser had to be stretched pretty tight for me to get it to fit. The nice gentleman at ACKits.com said that if there was a kink it would be quite obvious in that the system would not function even remotely well. I even called PA about this as the compressor is from them (and I just dropped big bucks there for my other car) and they basically told me that either I or the AC shop helping me was stupid for not knowing where the problem was. They then told me they had to go as UPS was there (another reason to use ACKits).

Matthew - the PA under belly condenser is where they really have you as it require special length hoses and fittings to install. If someone measured those hoses, then the only thing necessary to buy from PA would be the condenser itself.

[sammyg2]

OK, a couple things that could cause a very high delta P (high dischcharge pressure ans low suction pressure):

If the system had moisture in it you could possibly see icing in the expansion valve but prolly not. That usually shows up when the system works fine for 15 minutes then stops blowing cold air.

If the system was over charged you would definitely see high discharge pressures but I don't see how that would translate to higher suction pressures unless the staic pressure was also high. Have you measured the suction pressure when the engine is off and everything is equalized?

If the condensors are not functioning you could see a higher delta P than noral. Was the engine lid closed so that the air flow was directed through the engine lid condensor? That's all I have for now, lemme scratch my head some more to see if I forgot something.

[ZCAT3]

Thanks Sammy - I think the problem solved itself - the main issue seems to be that we were unwisely running the car at about 2500 RPMs with the lid open while checking the charge. It is surprising how important it is to keep the lid closed during this process - even though the engine fan does not feel like it moves much air. In any case, I am seeing vent temps in the low 40s with ambient temps in the 80s so I think the system is functioning properly.

[sammyg2]

Kool (pun intended)