Tube & Fin Condenser on Roof?

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Davo in Australia
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Tube & Fin Condenser on Roof?

Post by Davo in Australia »

I've got an 80s Range Rover here in Australia, with a new aircon I built a few years ago. I taught myself everything and built my own hoses since I'm in the bush and trades here are generally hopeless. It's worked well, but always really lost effectiveness above 35C or so. Below that and it's great. I put in a bigger evap last year which helped, but I'm going to change to a bigger condenser as I think that's the limiting factor. There's not much room in front, being an old British car, and also the engine temp goes up too much at the same time as the aircon struggles, so I'm betting that a rooftop condenser will solve both problems.

I'm just checking that this condenser, https://www.ebay.com.au/itm/25509782538 ... ctupt=true
(which I already bought, so I know I'm asking a bit late!), will be fine horizontal on the roof, with the fans on the "up" side. It sounds like the tube & fin design is fine for this, but being self-taught it always pays to ask those who actually know what they're doing!

System specs are: SD7H15, Hychill refrigerant, this type of evaporator, up next to the ceiling, behind the rear seats: https://coldmasterinc.com/product/unive ... v-223-100/

Thank you for any help, it's always appreciated.
ice-n-tropics
Posts: 128
Joined: Sat Apr 23, 2016 3:40 pm

Re: Tube & Fin Condenser on Roof?

Post by ice-n-tropics »

G'day Mate at the billabong, My 2 cents:
1) The condenser BTU rejection bogey is evaporator BTU absorption plus compressor drive input energy (horsepower in BTU).
Approx Condenser BTU = 22,220 (rated) + 7,777 (30% to 35% of evap absorption or use compressor curves at evap rating conditions) = roughly 30,000 BTU (at evap rating conditions).
Challange #1 is to get adequate condenser air flow from condensers shown. Tube and Fin can be compensated by powerful airflow. Rooftop motors must be rain resistant. Roof mounting to benefit from ram air is first prize.
Challange #2 is to get additional 12 volt generation to keep 12+ volt to 2 evap + 2 cond motors + comp clutch. May need 2 alternators.
Challange #3 is to optimize forced convection cabin air circulation to provide some spot cooling to front seat because cabin cool down w/o adequate air flow on front of occupants is inefficient.
Challange #4 is to optimize compressor borderline capacity with low pressure drop/ max diameter long suction lines and a KF compressor head with oversize suction port.
Caution: roof fans can be turned by ram air w/ AC off and generate power for unwanted clutch engagement unless operated via relay or back emf blocked via diodes (1000 volt rating}.
hotrodac
Davo in Australia
Posts: 15
Joined: Wed Aug 24, 2016 8:27 am

Re: Tube & Fin Condenser on Roof?

Post by Davo in Australia »

G'day! Thanks for making some points I hadn't thought about. It's always good to get someone else's view of these things.

#1 - If I could figure out how to post a photo I took it would help! It would show this condenser up on a full-length roof rack, where there's plenty of room underneath for a scoop, so ram air will be no problem. Fans will be SPALs and they seem to handle rain okay. (I am tempted to make a little rain cover anyway - I'm a bit precious like that. :D )

#2 - Funnily enough, I have two alternators with their own batteries already. So the plan is to run the condenser fans off #2 system, (with big cables and relays), and leave everything else running off #1 (main) system.

3# - The evap is up at the top of the cargo barrier, so airflow is usually good, just not too effective with 20C air coming out. It's absolutely freezing when ambient is a mild 28C, for instance.

4# - Good point, I was wondering about that. I always wondered what #12 hose was for!

I have two SPAL fans for the radiator and the current condenser and with big relays they don't backfeed - good point, though.

Do you have any thoughts on how much oil to add to the system? I'm trying to avoid taking out the compressor since it's buried down next to the engine.

Thank you!
ice-n-tropics
Posts: 128
Joined: Sat Apr 23, 2016 3:40 pm

Re: Tube & Fin Condenser on Roof?

Post by ice-n-tropics »

G'day Mate,
Oil quantity and liquid refrigerant migration:
After a cold night lowers the low mounted compressor housing temp the high mounted condenser warms up in the morning sun just like an agricultural tractor.
Result is that refrigerant migrates to the coldest part of the AC system (without oil) and condenses to a liquid inside the compressor. Also, refrigerant and oil collects in the low sections of the suction line and causes liquid slugging. If compressor's initial engagement is at 1000 = engine rpm:
1) compressor mechanism starts with a crankcase full of liquid solvent refrigerant but without oil on friction surfaces. A wobble plate Sanden SD7 critical friction points are the swedged connecting rod sockets which must have lube to avoid "DRY LOCK" seizure. Denso swash plate compressors lock up the swash plate surface to the piston shoes.
2) BANG! liquid slugs enter the compressor lower cylinders adding extreme loads to the swedged socket joints.
Some OEMs engage the compressor during starter cranking to reduce the possibility of compressor seizure. You can jog the compressor instead of full engagement startup.
More, and premium DEC Nippondenso oil helps.
Residual mineral oil from retrofit helps because it is not washed off friction surfaces by R134a. I have successfully retrofitted 7 Class 8 trucks without flushing the AC from residual/cling mineral oil but use very long evacuation to remove R12 from residual mineral oil.
Your oil quantity is probably unknown and remaining oil in crankcase cannot be determined without removing compressor.
I'd start with a min. total system of 300cc (10 oz. of DEC Denso PAG oil for TXV system) and throw in 3 oz. of non soluble Sanden R12 Naphthenic (not GM Paraffinic} mineral oil. Oil can be topped off anywhere into the system.
EZee countermeasure for challenges at 36 to 40 degree ambient in the Outback or a hot soak: Add a 350 psi pressure switch to shut off one of the evaporator fans or lower evap fan speeds.
My 2 cents hotrodac
Davo in Australia
Posts: 15
Joined: Wed Aug 24, 2016 8:27 am

Re: Tube & Fin Condenser on Roof?

Post by Davo in Australia »

Sorry, I forgot to check here yesterday!

Thanks for all the things you've pointed out, they are all things I wouldn't have thought of.

My system is so basic that it wouldn't be too hard to have the compressor clutch engaged during start-up.

I've got some Pag 46 coming over from Speedy Air Spares because it looks the same as the SP-10 on my compressor sticker. This compressor probably needs an oil change anyway, so if I can find an HF head and some #12 hose and fittings then I could do that all at once.

Good idea for slowing down the evap fans when it's really hot - that never would have occurred to me.

Thanks again, I really appreciate the help as I fumble my way through this.
ice-n-tropics
Posts: 128
Joined: Sat Apr 23, 2016 3:40 pm

Re: Tube & Fin Condenser on Roof?

Post by ice-n-tropics »

G'day Mate
KF Head with 1 1/16" threaded #12 horizontal suction port. not HF ???
Latest Sanden DEC SP10 PAG 46 is close to Denso PAG but Sanden SEC SP20 is NG.
If rooftop condenser doesn't dissipate heat that is absorbed by evap/comp, a series front of radiator secondary final condenser/subcooler may be required.
hotrodac
Last edited by ice-n-tropics on Mon Jan 10, 2022 11:22 pm, edited 1 time in total.
Davo in Australia
Posts: 15
Joined: Wed Aug 24, 2016 8:27 am

Re: Tube & Fin Condenser on Roof?

Post by Davo in Australia »

Argh! Yes, KF head! Posting at the end of the day is never a good idea . . .

Good idea, but hopefully this big condenser on the roof will do the job.

And thanks again!
DetroitAC
Posts: 133
Joined: Mon Oct 17, 2016 10:33 am

Re: Tube & Fin Condenser on Roof?

Post by DetroitAC »

I'm kinda late to this conversation, but why do you think a condenser is your biggest bottleneck? What are the pressures?
Davo in Australia
Posts: 15
Joined: Wed Aug 24, 2016 8:27 am

Re: Tube & Fin Condenser on Roof?

Post by Davo in Australia »

No, not late at all and I appreciate any help.

Sorry, no pressures as I don't have my notes handy, but they were normal for Hychill refrigerant.

The aircon works perfectly below about 35c, and above that it seems like there's just too much heat for it to shift. I also did the spray-water-on-the-condenser test and that lowered evap temps quite a bit, too.

The other reason is that the engine gets too hot at the same time so a remote condenser will help. It's an old British car in a hot climate, so no surprise really.
ice-n-tropics
Posts: 128
Joined: Sat Apr 23, 2016 3:40 pm

Re: Tube & Fin Condenser on Roof?

Post by ice-n-tropics »

Davo,
Wow! It matched the record of 50.7 C (123.3 F) in Onslow today. CAT operating in the open pit Ausse mines get even hotter radiation and conduction heat loads.
Testing AC in Death Valley, CA at 120 F and pulling a trailer up Baker Grade is our ultimate AC & engine cooling design validation. Record for DV is 134 F.
Climate chamber test spec for the military applications in Iraq and Afghanistan is 130.
hotrodac
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