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Registered
2007 E350
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38 Posts
Discussion Starter #1
My 1991 300E has a problem where the aux fans will not come on with the a/c. This causes the coolant temp to increase in traffic and the a/c stops blowing cold until you start moving again.

I do know the fans work because they come on at full speed when the temp gets above 110 or so.

Any suggestions as to what may be causing the low speed not to work? I was thinking possibly a pressure switch or maybe something in the dash control unit?

Thanks for the help, it's awfully hot in NC during the summer and an overheating Mercedes is no fun
 

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Registered
1991 300D 2.5 Turbo 305k, 2001 S600 110k, 2007 GL320CDI 4Matic 155k, 2007 E320 Bluetec 160k
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139 Posts
Same with me on my 91 300D... still looking for a solution.
 

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W124 Moderator
86 190E 2.3L 16V, 2 95 320TE's, 02 S500
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12,745 Posts
Low freon level or a bad pressure switch on the receiver dryer are the most likely suspects with your respective problems. Either of you had the A/C system checked?

Jayare
 

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Registered
95 E300, 91 300TE, 84 190D
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782 Posts
+1.

Jayare, are there also separate relays for low speed function and then high speed function, or just one relay for the aux fan?
 

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Registered
2007 E350
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38 Posts
Discussion Starter #5
I recently evacuated my system and recharged to the correct amount of r134 (converted by the previous owner).

I was wondering if maybe there was a different pressure switch required for the different pressures with 134?

Thanks
 

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W124 Moderator
86 190E 2.3L 16V, 2 95 320TE's, 02 S500
Joined
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12,745 Posts
There are separate relays for low and high speed function of the aux fans. Generally, if the low speed relay has failed, the high speed never kicks in. Replacement relays for both are "fused", 15/30 amp respectively. No, there isn't a "different" pressure switch for 134r systems that I am aware of.

Jayare

Sent from my DROID2 using AutoGuide.Com Free App
 

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Registered
2007 E350
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38 Posts
Discussion Starter #7
Problem Solved!

It turned out to be the resistor near the abs pump.
The resistor appeared to be okay but when I replaced it with a used one, my fans now work correctly.

Thanks for all the help
 
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