1961 cadillac conversion

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ice-n-tropics
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Re: 1961 cadillac conversion

Postby ice-n-tropics » Mon Jul 06, 2020 3:47 pm

Outside the box:
2xo is 75% correct that compressor swept volume displacement can solve your low refrigerant mass flow problem.
Suction gas flow restriction is the rest of the story. Relatively small suction hose I.D., bends and choke diameters inside fittings at the compressor should also be included in the capacity increase due to higher refrigerant mass flow per engine rev. Discharge and liquid hoses don"t matter.
A SD7H15 with a drive ratio of 1.5 for a 5500 rpm engine top end is a start for countermeasure.
I make stuff; and made a SD7H15 high performance compressor that exceeded the performance of a 10P20 0n a CAT using my KF head with a #14, !.25 thread suction fitting with over 5/8" ID bore entering the rear of the compressor straight in w/o bends. The compressor had other performance improvements. The suction hose was #14. Oil quanity was minimum with a TXV (less than factory safety factor.). The orifice tube kills performance because the oil quanity must be almost 75% more and the OT is a comprimise (ask any commercial AC guy). Use TXV w/o accumulator.
Mass flow and cooling is basically directly proportional the suction pressure at the intake valves.
hotrodac
Last edited by ice-n-tropics on Mon Jul 06, 2020 3:58 pm, edited 1 time in total.
cadillac matt
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Re: 1961 cadillac conversion

Postby cadillac matt » Mon Jul 06, 2020 3:55 pm

thanks for the info. what would be the advantage of the variable displacement? what mods would be neaded to use the v7?
cadillac matt
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Re: 1961 cadillac conversion

Postby cadillac matt » Mon Jul 06, 2020 4:00 pm

as far as the hoses. i have a gm style accumulator attached directly to the evap. that has a #12 outlet with a 90* reducer fitting to a #10 hose. about 2 1/2' of hose to a #10 90* fitting at the comp. the evap has a orifice tube built in at the inlet. is a txv possible? do i have to throw everything away and start over?
ice-n-tropics
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Re: 1961 cadillac conversion

Postby ice-n-tropics » Mon Jul 06, 2020 5:27 pm

basic sure thing is 5H14 is tooo small
cadillac matt
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Re: 1961 cadillac conversion

Postby cadillac matt » Mon Jul 06, 2020 5:56 pm

5h11, but yeah i'm seeing that.
Al9
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Location: Southern Europe

Re: 1961 cadillac conversion

Postby Al9 » Tue Jul 07, 2020 12:54 am

cadillac matt wrote:thanks for the info. what would be the advantage of the variable displacement? what mods would be neaded to use the v7?

Advantages? No cycling, less engine load as cooling demand decreases (the evaporator will actually get cooler as ambient temperatures go up, since the valve uses the discharge pressure to set the suction pressure setpoint). No evaporator temperature sensor/cycling switch. Want the evaporator to get colder or warmer? Just exchange the control valve with one of a different color until it suits your real meaning of AC.

Disadvantages? Using a TXV with one is a hard task. Really vulnerable to low refrigerant and low oil return conditions. Can be annoyingly noisier than other kinds of compressors especially when something is wrong with the system.

If you want to use a TXV with one, you need to make sure this TXV will be always feeding the evaporator with some refrigerant even at low heat loads. I.e. it should never ever modulate to 0 flow. Either a nicked valve seat or a special operating charge made from a mix of different gases. Or when the system is run with low heat loads (i.e. defroster in cool/cold weather) it will hunt and interfere with the compressor control valve (resulting in a really unstable vent temperature esp. at low blower fan speeds) and possibly cause compressor damage/seizure due to no oil return while the TXV is fully closed. It also needs to be carefully tailored to the evaporator's maximum cooling capacity so that it's steadily fed at any heat load, and the operating shaft isn't supposed to be what transmits heat to the operating charge.
Just so you know, the original TXV for my car, which features an updated version of the V5/V7 compressor, never snaps shut when you freeze the power head with freeze spray. The metering pin just moves a little closer to the orifice and that's it. Air keeps flowing through the orifice albeit at a slightly, almost unnoticeably lower flow rate. That is, instead of maintaining a fixed superheat at all times, this one has a high superheat (as high as 10K or even more?) at high heat loads and goes 0 superheat once the evaporator is cold enough. The thin operating shaft is covered in a thick resin sheath.
Some serious research/trial & error ahead when choosing a TXV meant for a variable displacement compressor.

For your peace of mind, just use a non-variable orifice tube. Slightly less efficient but hassle-free.
Last edited by Al9 on Tue Jul 07, 2020 1:04 pm, edited 2 times in total.
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bohica2xo
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Re: 1961 cadillac conversion

Postby bohica2xo » Tue Jul 07, 2020 10:44 am

GM installed V7's in Orifice tube systems. Yes, you give up a little performance with increased OCR. You could add a TXV if you want - just remove the orifice tube & plumb it in. Adding a receiver to the liquid line in the process. I would start with the O/T setup you have & go from there.

Ice is right, you need to use a -12 suction line for the bigger compressor.

Unless Ice is willing to sell you a handmade compressor, the V7 is a good off the shelf unit. A TM21HX would do the job as well, but I have not seen an ear mount one in a long time.

Depending on how you control the LS, you could run a better drive ratio. OEM systems cut the compressor when the engine rpm reaches the danger zone for the compressor. The compressor can be driven faster at idle.
ice-n-tropics
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Re: 1961 cadillac conversion

Postby ice-n-tropics » Tue Jul 07, 2020 11:17 am

SD5H11 LOL
You may need to modify OEM blower inlet in AC mode for 100% recirculating air. At 95F/50%RH most OEMs will meet or beat 45F discharge air with 100% recir air but the boggy is only 55F with full outside air. I usually install a shut off water heater valve for summer cooling on vintage OEM AC
hotrodac
cadillac matt
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Re: 1961 cadillac conversion

Postby cadillac matt » Tue Jul 07, 2020 7:12 pm

wow. thanks guys. that's a lot of info to digest.
so let me get this straight. i want a v7 comp. i need to bypass the cycling switch.
the air ducts are at 100% recirc already and the car has a factory heater core shutoff. the a/c air doesn't go through or from the heater core anyways.
as far as the ls a/c controls there are none due to the e38 ecm needing a bcm to do that, so the a/c is standalone.
so final questions(i hope), what mods are needed to adapt the v7? and what ot should i use? has a blue 1 now. as far as the #12 suction,the accumulator has a #12 outlet, does the v7 have a #12 inlet?
thanks again.
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bohica2xo
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Re: 1961 cadillac conversion

Postby bohica2xo » Tue Jul 07, 2020 8:32 pm

The V7 uses the block style suction / discharge setup common to GM products. I know there are aftermarket blocks out there, as well as OEM stuff.

Here are a couple of GM part numbers for V7 suction / discharge hose sets, see if you can find one locally to look at:

10229469, 19213199, 15034761, 19169363

The V7 clutch simply needs +12v to pull in, the control valve handles the rest of it. You can control cabin temperature by simply reducing blower speed.

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