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Parallel flow condenser

Started by 1980sdga, 29 June 2011, 07:50 PM


Jon, I don't know if I was clear about the cycling switch, In the original set up, as I indicated before, the temperature probe "sensor" which is installed in the evaporator, will cycle the compressor when the evaporator has reached the set temperature, you should also have this already installed in your evaporator. This has worked for me as  the compressor cycling switch. In a typical Orifice Tube system, they install a pressure or temperature cycling switch on the accumulator itself. I see no need for going this direction specially if you are going to install the original pressure switch on the receiver/dryer, my original pressure switch which I installed on the connection piece as I said before, has a dual function. It will switch off the compressor if there is low refrigerant level or no refrigerant in the system, or if the pressure is too high.

Walla, as I stated before, our w116 are already prepped  for a relatively easy switch to Orifice tube.

If you want to have a typical OT system with a cycling switch on the accumulator, I will work with you to accomplish that,, but in my opinion , there is no need.



Thanks bolbol!  I'm basically trying to replicate your system and hope it works here in the hot humid southern US!  How exactly does the evaporator switch work?  Does it have an on/off parameter that turns the compressor back on once the evaporator warms a little? How often does your compressor cycle?  I have the ACC system and it has the temperature switch on the evaporator.

I also used #6 hose between the condenser and evaporator and the OT holder is a larger diameter. Looks like you used #10 hose?

Here's a picture of the holder I put together:

You can see how the hose diameter is actually smaller than the tube. I'm not sure if this narrowing will have any ill effects  ???

I too looked into running both a receiver AND an accumulator and got about the same answers you did so I figured I'd try it out.  I already had the part.

Thanks again for the inspiration to do this!



Hey guys, a few observations from here: first off I can't see any operational penalty in having a receiver/drier in the system as well as an accumulator. Bolbol's replacement solution looks very neat but are you saying you have

no filter or drier in your system bolbol? An accumulator provides no filtering or drying of the refrigerant and it would be most advisable to have a filter/drier in the system with an orifice tube, without necessarily having the

receiver function as well. I can't see why having a new type condensor would lead to higher liquid temps or pressures, as long as it is sized to suit the other components it will work just as well as any other condensor.  Jon,

you will still need the safety switches as bolbol says. Cycling the compressor off the thermostat in the cabin shouldn't be a problem, one thing to watch out for here is that it doesn't cycle on too soon after having switched off.

The compressor will not like starting again if the high side pressure is still at or near it's operating pressure, the system must have enough off time for the pressures to equalise or at least get somewhere near equalising,

otherwise the starting torque required will be way too high. This time will depend on conditions but I imagine you would need at least 60 seconds off time to allow pressures to approximately equalise. Can't see your hose

diameter coming into the orifice being a problem Jon, all looks good there. 

Keep going, looks good!!


Jon, please look at 83-542 in the Library, it lists specification and parameters for the temperature switch. In picture 183-8767 please take note of the switch and figure "3" the thermostat that goes into the evaporator.

Ken, with all respect, the Accumulator I fitted does have Desiccant and screen for filtering and drying, but I agree with you that a receiver does a better job at that, I will fit either an in-line filter or install a receiver/dryer next year,, awaiting the outcome of Jon setup.

Regarding higher temperatures of coolant, I just know from experience that the parallel flow condenser and the larger electric fan might block some of the air sucked in by the engine fan and will counter effect the flow of air marginally,, I just wanted Jon not to be allarmed if he sees higher temps.

Another note of interest, I am running at 20-30 PSI low side and 150 PSI  high side,, at 28C  , RPM at 1700.



Quote from: bolbol on 17 July 2011, 02:00 AM

Ken, with all respect, the Accumulator I fitted does have Desiccant and screen for filtering and drying,

Ah ok, I stand corrected. I think (hope) I said somewhere before that it's been a while since I did any vehicle a/c. I haven't heard of a beastie such as this but it sounds like a good idea. Which refrigerant are you running

Bolbol? Your figures sound pretty good for r12. Interesting to hear your experience of a slight air flow restriction with this style of condensor, do you think that it's simply down to the higher density per face area of the fins?



Thanks for the input guys!

My car has ACCII which doesn't have the dash mounted temperature switch. It does have an "ETR" (Evaporator Temp. Regulator) in the compressor circuit which turns the compressor off at 36F.  I can't find anything about how/ or if it turns the compressor on when temps rise  ???

It is also quite inaccessible  ::)  requiring dash removal to change  :o  It's right beside the center vent vacuum pod...

I have isolated the wires that run to it and there are lots of evaporator temperature switches available so maybe I could leave the original in place and retrofit another one?  Maybe one that turns the compressor OFF at 34F and back ON at 38F?  I would have to figure out how to fish the capillary tube into the evaporator somehow.

Maybe my existing ETR will be fine.

About the accumulator. Most older US cars that I'm familiar with (Actually trucks, with COLD AC) use an OT and accumulator and they don't run receivers. The standard GM accumulators have filters and dessicant in them.  I just decided to put the receiver on my system because I had it and it would make it easier to change back to TXV if I had to and the consensus is that it'll work. It is uncharted territory though  :D

Good point on cycling the switch too soon Ken!  I hadn't thought of that but I understand what you mean.

Just kind of anecdotal but...

I was fooling with the condensers and the new fan and it did seem like there was more airflow through the old condenser and the new one.  Not very scientific but just by "feel" it seemed that there was more air moving through the old one.

Thanks again for the help guys!  I've never even fooled with auto AC systems so I need all the help I can get  :o

It's mostly faith and wrenches...

I had to move the condenser an inch and a half towards the left in the pic. The fan is in the same location.

I didn't like the receiver sticking out so much.

Previous location:

The condenser is now a lot more centered with the radiator.


Ken, I was running r12 at some point before, and I was curious to run R134a because of availability issue of r12. So now I am running r134a and I hardly can notice any difference in temperatures or pressures. I think the condenser and double fans I installed are doing an adequate job at keeping pressures low, and you are absolutely correct regarding the parallel flow condenser having higher density, fins, per square inch and I think PFC ads another source of heat to w116's copper radiators to deal with

PFC are aluminum which radiate heat better than copper, that's good, but this heat is pushed through the radiator, that's marginally not good. If you have a maintained cooling system, then running few degrees higher should not be a problem. (based on my experience of installing a PFC off an W146 S500 on a W116).

Jon, I have almost no experience on AC II, which you have, but if your vacuum switches and AC electricals are working properly, then the ETR should give an electric signal to the compressor to switch on and off (cycle) at the set temperatures.



Finally getting the accumulator in place:

Still waiting on the #12 hose for the suction line from the evaporator.

I've had my accumulator open and I understand that it is bad for them but I didn't have a choice  ???

Any advise on this?  Should I go with a new one when I do the final connections?  Seems like a shame to throw out a never used accumulator...


Just make sure you get a good vacuum on the system Jon and hold it under vac for several hours, it should remove any moisture accumulated in the dessicant. It can also help to break a vacuum a couple of times and pressurise the system with dry nitrogen, helps to get a good final vac.


Finally got the hose crimper:

It seems to work pretty well. I have most of the hoses built but I need to make the hole in the firewall larger for the high pressure line to enter the cabin.

I've been working on this forever...


I finally started her up today  8) 

Got the oil cooler lines fixed and routed, rad. in, etc. Now it's just AC stuff...

This was the hold-up:

I used my AC hose crimper to repair my oil cooler line  ;D


Did some testing today:

The low pressure was 30 psi and the high side was 200 psi at idle with 2 lbs of 134a.

I'm going to run it some more and check for leaks. Maybe add another 8 oz of 134?

I ended up using a .62 orifice tube but I may try a .072 and see how it works.

It did get down to 40 F when rolling so I'm happy  :D  Not super enthused but happy!

Any input?

Ken, Bolbol?


Hey Jon,

Nice work, and congratulations on sticking with it and getting a good result. Sounds like you are well on the way, 40f air off is pretty good I would think, the way we alway used to test them was open all the doors, stick the fan on high, stick a brick on the accelerator so you maintain about 2000 rpm or so and then check your pressures etc. Your high side needs to be a fair bit higher than 200, would think about maybe 270 or so at that speed from memory. Then check your air off temp and you can adjust the charge from there. You must make sure to check the superheat at the compressor to be sure you don't overcharge it, don't know how this would play out with an orifice tube assembly but normally you would want at least 2k of superheat at the comp to be sure you aren't flooding back. This will change too with revs and load within the car so check it when the car is cool inside as well.
Looks like you're nearly there, just in time for winter as you were saying earlier...he he


Thanks Ken!  I was mainly just charging it to test for leaks and such and if all seems OK after a few weeks of running I'm going to vacuum the system and check the OT to see if the filter picked up any junk.  Everything is new except for the evaporator which I flushed.

I had a shop do the vacuum/charge and I didn't want to monkey around too much on their dime!

I plan on getting my own vacuum pump and a set of gauges for the future.

I'm not sure if I need to worry about superheat values with an OT because the accumulator is supposed to make sure all the refrigerant is vapor before it hits the compressor.  The accumulator sweats quite a bit and it's running about 45 F. 

How do I arrive at the superheat value anyway? And do I just check it at the compressor suction line with an IR thermometer?

  When you say "air off" what do you mean exactly?

Thanks again for the help! Your advise has helped me a WHOLE LOT with understanding how these things work!


Yeah the accumulator is supposed to hold any liquid refrigerant and prevent it from going down the suction line to the compressor as you say Jon, would still check the superheat to be sure. The way to check is take your suction pressure and then either use a pressure temperature chart or you might have a temp scale on the gauge face, so the temp corresponding to the suction pressure is the temp of the refrigerant leaving the evap. Measure the temp at the compresor suction inlet and you should have a higher temp by  a few degrees K (celsius), minimum  2 for safety. It will vary of course with engine revs, heat load and will be more likely to flood at lower load. You want a digital thermometer, or IR that will react quickly to temp changes. If you have a digital thermometer with a probe, place it at about 4 or 5 o'clock on the pipe because any liquid is likely to be at the bottom of the pipe and will be picked up by the thermometer, tape it on and cover with a bit of insulation to prevent any false signals from ambient temps. Air off means the air temperature off the cooling coil, as opposed to air on.
Good luck,