Hi I have a 95 e300 which I got a couple of months ago. The ac is not blowing cold air. Compressor clutch wasn't engaging and it didn't have freon because it seems has a leak somewhere.

I charged it with freon and the compressor clutched engage but acc fan did not turn on. I jumped the coolant sensor and the fan ran on and off. AC did not blow cold air. I checked the condenser it looks clean.

What else should I test? I checked the coiled resistor with a vometer and it good.

Can I jump the compressor? if yes, how?
And what are these sensors? Thanks

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1984 190D 160,000 miles -sold
1992 190E 124,000 manual 2.3 -sold
2000 c230K 84,000
1995 e300 134k

Those are both pressure sensors. One turns on the aux fan in low speed, the other decides whether to allow the compressor to engage the clutch. If the pressure is either too low or too high it won't allow it.

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
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"Oh lord won't you buy me a Mercedes Benz."
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Thanks for the reply. Which one is for the low speed fan 1 or 2 (in the pic)?
So if the clutch engages the ac should blow cold air?

What else can be the culprit if the ac still blows warm air even there is freon and the compressor clutch working? dead compressor?

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1984 190D 160,000 miles -sold
1992 190E 124,000 manual 2.3 -sold
2000 c230K 84,000
1995 e300 134k

its no.2 sensor, it should have two brown wires - it routes ground power to the low speed fan relay to start the fans low speed.

I would suggest you first check the fan circuit by manually verifying the fans are good, remove the 2 wire connector held in a metal clamp and feed it ground and power, if they run you are good.

test the low speed circuit by removing the (sensor two wires) in your pic and joining them together (join the harness side) - the fans should run low speed, if they still dont you need to verify that you are getting voltage at the step down resistor that is bolted right next to the reciever drier, it is known to burn the wiring after the resistor.

If you still dont have voltage at the leading point of the resistor after you shorted the pressure switch wires then you need to check the fuse to the low speed, its on the relay itself which is in the relay panel behind the fuse panel in the fuse box. The relay is a blue one and has a 15A fuse originally a 20A fuse is accepted and recommended by MB dealerships to prevent short life.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)

Thanks for the help Zulfiqar. That sensor which control my low speed fan is dead cause when shorted the low speed fan runs although only one fan works I think the other fan is dead.

I will order the sensor asap. Will it fix my AC problem of being not cold? I recharged again my AC, and shorted the sensor to turn on my low speed fan and it still blows hot air.

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1984 190D 160,000 miles -sold
1992 190E 124,000 manual 2.3 -sold
2000 c230K 84,000
1995 e300 134k

The sensor is exposed to refrigerant so replacement requires that you evacuate the system first.

What do you mean by "I recharged again my AC?" How long before there isn't enough pressure to engage the compressor? The proper way to recharge is, at minimum, to pull a vacuum on the system to verify a closed system then fill with a measured amount of refrigerant and lubricant. To do so, you need a manifold gauge set to check static pressure and, with the compressor engaged, low and high side pressure. Recharge-in-a-can kits only mask slow leaks in a system with just less of a charge than the minimum the compressor switch requires. If your system is basically discharged, such a kit won't displace ambient air in the system and moisture saturating the dryer. You need to pull a vacuum first and most likely you need a new dryer.

Sixto
87 300D^2

Thanks Sixto for the reply. My ac has a slow leak somewhere as it looses half of its pressure in 2 weeks. I will have to bring my car to a shop because I don't have the equipment and the know how to pull the vacuum. I just used a can recharger to engage the compressor. I guess I can change the sensor and the dryer then bring it to a shop to cut some cost.

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1984 190D 160,000 miles -sold
1992 190E 124,000 manual 2.3 -sold
2000 c230K 84,000
1995 e300 134k

I'm not an AC expert but if the system has remained under pressure to a reasonable degree and you're ready to open your wallet for a shop, maybe you can first try a chemical leak stopper. There's lots of lively discussion on the pros and cons of hydrocarbon refrigerants but I've heard generally good things about these sealing products:

http://autorefrigerants.com/stopleak.jpg for rubber and http://autorefrigerants.com/proseal.jpg for metal from Enviro-Safe Refrigerants

Again, I'm only suggesting the sealing products. Let's see how long before this becomes a HC thread. Flame suit on.

Sixto
87 300D^2