Actual A/C ΔT that most obtain

[sjh]

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We have some excellent, skilled, highly-knowledgeable A/C people on this board. They have first-rate equipment many different chemicals and have invested significant time and money.

Most of us do not fall into that category. I'd like to know what temperature differences between outside ambient and center vent temperature most of us experience.

So if your driving on the highway, bright sun, but not laser-like and the outside temperature is 90 F what temp do you measure coming out of the center vent at it's coolest?

I get 54 F for the conditions described above. I wish it was 44 F but I can't justify the time/effort to return my system to R-12 (I'm not the guy who altered it) and I'm not certain that the effort to pull the wipers and foam the coils is worth it either.

Unless I get 'creamed' by the 'wise men' on this thread let's keep the discussion to the 5-button and earlier CCU's. Thanks.

[ForcedInduction]

54 is very good for inefficient R134a.

Make sure the heater modulator is fully closing.

[Doktor Bert]

Originally Posted by sjh

So if your driving on the highway, bright sun but laser-like and the outside temperature is 90 F what temp do you measure coming out of the center vent at it's coolest? Thanks.

1978 300SD in Central California with a true R-12 CC-II system using genuine R-12 refrigerant.

On a 100°F day at 50-70 mph I get 42°/44°F in the center vent and during prolonged periods of idle in the same weather, I get 46°/48°F in the vent, both in direct sunlight.

The auxillary fan cycles on and off when the A/C is operative. I also use the later 9 blade plastic fan, which actually causes the auxilliary fan to rotate at idle speed...Robert

[sjh]

Originally Posted by ForcedInduction

54 is very good for inefficient R134a.

Make sure the heater modulator is fully closing.

Thanks. I don't want to rock the boat.

Is the HM a valve that controls the flow of hot water to the heater core?

Would it make sense to try bypassing or altering the temp cut-out switch near the compressor or am I 'playing with fire' if I do that?

Also I get pretty much the same results whether in recirc mode or drawing ambient. I'm thinking that is because the system is automatically 80% recirc when it's that hot outside. Make sense?

[sjh]

Originally Posted by Doktor Bert

1978 300SD in Central California with a true R-12 CC-II system using genuine R-12 refrigerant.

On a 100°F day at 50-70 mph I get 42°/44°F in the center vent and during prolonged periods of idle in the same weather, I get 46°/48°F in the vent, both in direct sunlight.

The auxillary fan cycles on and off when the A/C is operative. I also use the later 9 blade plastic fan, which actually causes the auxilliary fan to rotate at idle speed...Robert

My aux fan has NEVER kicked on.

But I seldom am above 90 and when I am I'm doing highway driving.

I'm in coastal Calif and have only had one afternoon in sacramento when the system did not work well enough.

[ForcedInduction]

Originally Posted by sjh

Is the HM a valve that controls the flow of hot water to the heater core?

Yes.

Would it make sense to try bypassing or altering the temp cut-out switch near the compressor or am I 'playing with fire' if I do that?

Yes. Increasing the temperature increases pressure. You can seize the pump or blow a line if it gets too hot.

[Brian Carlton]

The SD with R-134 in 90 degree ambients:

Vent temperature after 30 minutes (cabin at setpoint):


47F. on high blower speed.

41F. on low blower speed.


The evap will reach the trip for the ETS and the vent temp will begin to fluctuate between 41F. and 50F.


When properly setup, R-134 functions perfectly adequately for ambients below 95F.

[Doktor Bert]

Originally Posted by sjh

My aux fan has NEVER kicked on....

It should.

My wife uses the 300SD for her Mark Kay business because it has better A/C than her 2008 Dodge Magnum. I routinely start it and let it idle about 10 minutes before she leaves to keep the product cooled.

Within a few minutes of starting, even in 85° to 90°F weather, the aux fan kicks on and off.

[sjh]

Originally Posted by Brian Carlton

The SD with R-134 in 90 degree ambients:

Vent temperature after 30 minutes (cabin at setpoint):


47F. on high blower speed.

41F. on low blower speed.


The evap will reach the trip for the ETS and the vent temp will begin to fluctuate between 41F. and 50F.


When properly setup, R-134 functions perfectly adequately for ambients below 95F.

OK, I'll try to get cooler.

[cjlipps]

I feel pretty fortunate. It's been routinely over 100*F here and even at 110*F I can reach 40-42*F at the center vent on the highway on medium fan speed. It will also hold 50*F at (fast) idle in the sun. Of course this is with the thumbwheel in the "max" position for as much recirc as possible. The aux fan runs nearly all the time, sometimes even before the car is warmed up and the a/c is cranking.
I recently (or rather my indy) installed a new compressor and r/d and am still using the beloved R12.

[tangofox007]

Originally Posted by cjlipps

Of course this is with the thumbwheel in the "max" position for as much recirc as possible.

Does the recirc/fresh air flap respond to the position of the temp selector?

[cjlipps]

Originally Posted by tangofox007

Does the recirc/fresh air flap respond to the position of the temp selector?

I can hear a faint pop in the dash as I go through the detent to the "max" position so I'm thinking it does. The temp wheel works as I think it should at other settings also.

[sjh]

Originally Posted by Doktor Bert

It should.

My wife uses the 300SD for her Mark Kay business because it has better A/C than her 2008 Dodge Magnum. I routinely start it and let it idle about 10 minutes before she leaves to keep the product cooled.

Within a few minutes of starting, even in 85° to 90°F weather, the aux fan kicks on and off.

I'll have to figure out why.

I'm thinking of finding the voltage to the A/C clutch and then monitor if the compressor is cutting out or running continuously while driving on the highway.

Reading the above 90 thread that is currently winding down I have been measuring the temp incorrectly. I had fan on max and all vents open for measuring.

It seems the fan should be slower. Do I measure the temp with fan in auto position?

[sjh]

Originally Posted by tangofox007

Does the recirc/fresh air flap respond to the position of the temp selector?

When I took the dash off last year and did all the pods I mity-vac'd everything and the recirc mode worked. i also tested the manual switch and it sent the right voltage to the vac relay behind the g. box and that worked.

However, when I drive I do not hear anything (besides the relay under the back seat) when the recirc switch is pushed. So I do not for certain that the min setting is causing the flap to close. I can test that with a vac gauge. Thanks.

Reading what others are saying it's clear my A/C is not moving as much heat out of the cabin to the front heat exchanger before the radiator. I'm probably good for this summer and will start to strategize what to do.

Thanks for everything.

[Doktor Bert]

Since I added full window tint to the car, my vent temps on a 100°+F day are in the 33°/36°F range with R-12 on the freeway and 38°/40° idling in traffic with auxilliary fan kicking on and off....

Note: Felt cover removed from ETR and ETR adjusted to yield 34°F in the center vent. Fins on condensor cleaned and straightened, NEW exapansion valve with drip-tape covering as per factory, EXACT amount of mineral oil and refrigerant precisely measured and introduced into system.