Automotive Air Conditioning Information Forum

Okay I think I have this working as well as can be expected now.

92F, 60% humidity today.

I got the charge close to where I think it should be and decided to test it on the road, in true operating conditions. I won't ever drive this car in any weather hotter than this so it's a valid peak load test I think.

I added charge until the compressor would stop cycling, as it should on a 90+F day.
At 60mph steady, it settles out to 26psi on the low and under 240 on the high side, and blows 42F from the vents. Around town stop/start it will go to 50F
Cycling switch is set at 22psi. I don't have gauges on it while driving, but I know the high side fan switch for the condenser closes at 240psi and I put an LED inside the car, connected to the fan relay to give an indication of where the pressure might be. It switched the fan on if stationary for a few minutes, but went straight back off again when the car started moving again. I might fit the gauges and drive it again tomorrow as I'd like to know the actual numbers. Today's test was just to determine if it was 'crazy high pressure' or 'likely safe'.

The low side probably indicates it could swallow a touch more refrigerant, but I think it's working quite well now so I'm going to monitor it before making any more changes.

The r4 scroll compressor is far smoother and seems to put much less load on the motor than the regular piston R4 - probably because it's not moving as much refrigerant, but it's much nicer in it's operation. I can't even tell when it cycles. Maybe it would struggle in a dual AC van, but it seems to work okay in this small cabin car.

Thanks for you guidance.

wetlook wrote: ↑Tue Mar 07, 2023 9:11 pm At 60mph steady, it settles out to 26psi on the low and under 240 on the high side, and blows 42F from the vents. Around town stop/start it will go to 50F

The pressures look pretty good at that speed (~2,000 RPM??) and ambient (+90°F), and the vent temperatures are probably as cool as they're going to get. At 26 PSI, the evaporator will be approximately 32°F.

wetlook wrote: ↑Tue Mar 07, 2023 9:11 pm Cycling switch is set at 22psi. I don't have gauges on it while driving, but I know the high side fan switch for the condenser closes at 240psi and I put an LED inside the car, connected to the fan relay to give an indication of where the pressure might be. It switched the fan on if stationary for a few minutes, but went straight back off again when the car started moving again. I might fit the gauges and drive it again tomorrow as I'd like to know the actual numbers. Today's test was just to determine if it was 'crazy high pressure' or 'likely safe'.

Sounds like normal operation to me.

wetlook wrote: ↑Tue Mar 07, 2023 9:11 pm The r4 scroll compressor is far smoother and seems to put much less load on the motor than the regular piston R4 - probably because it's not moving as much refrigerant, but it's much nicer in it's operation. I can't even tell when it cycles. Maybe it would struggle in a dual AC van, but it seems to work okay in this small cabin car.

I think you're correct in that the R4 piston version would pump more efficiently and might cool a little bit better than the scroll. You could try adding an ounce or two of refrigerant from where you are now while monitoring the vent temps and pressures. But it appears to me that you've already reached the optimum charge.

" I know the high side fan switch for the condenser closes at 240psi "

If it were my car, or a customer's, I would wire the condenser fan to come on anytime the comp is on. Why wait?

The condenser fans are almost never wired on all the time like that by OEMs, it just wastes power/gasoline and wears out the fans. I'd leave it operating on the pressure switch unless there is a compelling need to change.

2000 to 2004? Dodge Neon was that way, was done to reduce costs, there wasn't any pressure switch or sensor. At moderate to highway speeds the fan wasn't doing anything but wasting energy. The Neon should never be your standard for how to do things

LOL the OEMs do a lot of things I am not fond of. Certainly once the fan is on it really isn't gonna go off very often.

hi
What OP needs to do is measure pressures during 60mph h/way and idle plus crawl at 20mph . Try with fan ""on"" pressure switch and completely disconnected then connected on with compressor . Measure the pressures ,what are they ?? This will tell u if the fan thats fitted is doing alot or little .

Change fan if required . Bigger flow is better Spal 13 inch would be great .

Biggest issue for constant fan [compressor on ] operation is alternator capacity .

Although 240psi is measured and sure many systems run at this level . I would consider only satisfactory . Ideally closer to 200psi would be great for a single condenser system .

RH drive USA car air con is a big compromise
Re high pressure liquid line temp 65 deg cel is very hot and 45deg cel is regarded as cold . Engine air temp is 80--100deg cel . Exhaust temp far hotter .
Ceramic coat headers /manifolds and insulate evap box .
Highly recommend cover evap box with sticky back insulation foam with aluminium fascia sheet

hi
Picture showing GM RHdrive evap box
large hole blower fan ,,small tube blower fan cooling tube
medium hole evap box suction line exit

Sticky fibre glass insulation aluminium coated top /bottom /sides
NB CAUTION some insulation is cheap foam and very thin foil. This is fibreglass insulation with good durable layer of alloy sheet
Its so sticky u cannot re-position pieces , u just cut a new piece

Insulating under the hood etc is never a bad idea.
Fiberglass header wrap is always a good idea, and FW and air box if you can get at them

And I should qualify my response above....we mostly work on vintage vehicles that never see the highway, so they never get the benefit of high speed air movement thru the condenser

hi
Long term header wrap crystalizes , the header tubes . What? The wrap holds the heat in so well the steel then reaches temperature well above the normal range . In turn it deteriorates the metal eventually collapsing the tube.
Solution is to ceramic coat valuable expensive /rare parts .

Both wrap and ceramic coating reduce heat well .

hi
Many 60`s and 70~ cars had extra insulation on airconditioned models
under bonnet / hood
xtra firewall insulation engine or cabin side
air con evap boxes located in engine bay
different undercarpet insulation
radiator and condenser foam /material strips more for air ducting
cowl weather strip

*** unfortunately , much of this is removed or deteriorates and not replaced so 40-50yrs on people assume it was not fitted .