AC Evaporator/Vent/Fan Different Temperatures... is this Normal?

1985 300TD... OK... It's 90F or so here in New Orleans right now. Humidity probably about 80% as its been humid and raining off and on all day.

I'm doing some highway driving on I10 and on a 3 to 4 lane local road Airline Highway to test the AC. I am using Analog and Digital thermometers in the center vents.

With the AC on and the Fan on Low (bottom switch) I get a reading of 38F.
Switching the Fan to Auto the temperature rises to 54F after awhile.
Switching the Fan to High the temperature rises to 60F.
Bringing the Fan down to Auto drops the temperature to 54F.
And lastly switching the Fan to Low brings the temperature down to 38F.

Everything cycles as it should (I think)... all flaps seem to be working properly and the air is being directed where it should be.

Now... is there flap that should be recirculating the air from the cabin? The intake on the blower is pulling air from under the dash directly above the blower. When I put the Climate Control on EC the temperature does rise to about 80F as it seems to be drawing air from the vents. Switching back to AC results in the temperatures described above. Does this seem normal? Why is there such a huge increase in temperature as Fan speed increases?

Thanks in advance -- dennis

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'84 300D (211k) *New*... (Wife's)
'85 300TD (174K) 10th Year... (Mine)
'96 F-350 7.3L Dually (149K) Since New
'85 300D (156K) ~~~Wrecked~~~ Damn it! (parts)
'84 300D (176k) ~~~Wrecked~~~ Damn it! (parts)

Bump


Charlie

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there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works

I imagine the W123 has a recirc flap like the W126 to pull air from the outside. If that is not working properly, you could be trying to cool hot outside air all the time. If you turn the temp wheel all the way to the blue and it clicks in place, the outside air flap should close and you should be recirculating cabin air. If all of that is working, you could have a partially clogged evaporator and as such, it can't handle the extra air being passed through it. All of this is assuming the AC system is charged properly.

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1991 F250 super-cab 7.3 IDI. (rebuilt by me) Banks Sidewinder turbo, hydroboost brakes, new IP and injectors.
2003 S430 - 107K
1983 300SD - Tanoshii - mostly restored ~400K+.
1983 300SD - Good interior. Engine finally tamed ~250K.
Monark Nozzle Install Video - http://tinyurl.com/ptd2tge

At high speed more air is blowing with the same amount of cooling, so the air will be warmer. Auto is likely between low and high as far as speed is concerned.

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'97 E 300 D

Sounds pretty normal to me. With the fan on higher speeds, the evaporator probably struggles to absorb as much heat and transfer it to the condensor. This will probably be more noted if the evaporator is dirty and blocks some of the air flow.

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Sam

84 300SD 350K+ miles ( Blue Belle )

Minimum blower speeds allow the air to stay in the evaporator longer. This allows them to cool down better. Opposite is true with higher blower speeds.

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http://farm8.staticflickr.com/7271/7...144c3fc1dc.jpg

Sounds like you are low on refrigerant. What are your pressure reading?

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'85 300D Cal 280,000 miles
'14 GLK 350 60000 miles