New to me 1993 300e 2.8L

[Paulhorner]

Hello.
Just acquired 1993 300E 2.8 L.
Blower motor is running on low speed only regardless of fan or temp setting.
Getting cold air but very little of it.
Can anyone suggest any fix other than a frightfully expensive blower motor regulator?

Also with ac on full it is prone to overheating with no high speed action from the aux fans. Ceramic resistor behind driver headlight would supply low speed power only??

Anyone think these two ailments are related??
I have not checked the amount of refrigerant in the system. Would topping up refrigerant effect either issue.

One last thing I understand this model used 34a but the connectors are the larger couplings that is commonly on R12 systems. Could be a transition year and they used the old fittings with the new gas???

Thanks

[Paulhorner]

Update
When blower motor is disconnected and car engine running available voltage is 13.6 to 13.9 across all fan settings amperage unknown.
With blower motor connected and engine running 3 V across all fan settings.
Bench tested blower motor with 12v quick on and off ran extremely fast.
Would this indicate faulty blower motor regulator?
With Key on and blower motor disconnected 12.6 V at blower motor leads.
Battery is new.


Auxillary fans.....with key on jumped across leads at blue sensor/switch on thermostat. fans came on high... Is this correct?

With key on jumped across red sensor at receiver fans came on low.....correct?

[Paulhorner]

Can someone please tell me the amount of voltage delivered via the pbu to the blower motor in low and high fan speeds?

[pawoSD]

The regulator can fail, I've seen it happen before. On high/full speed the regulator is bypassed and full power goes to the blower. Could always look for a used or rebuilt regulator....

Its possible the climate control unit itself is faulty and is not triggering the regulator to the proper speeds.

[pmckechnie]

Paul,

Find the cable coming from the blower motor/regulator. I think it is between the brake booster and the center of the car. I can't remember if it is in front of or behind the false firewall but it is somewhere around there. Three wires Brown, Black/Green, and White/Pink. With every thing connected, engine running, you should see 12v+ between the B/G and Br wires. Then check the voltage on the W/P wire to the Br wire. It should be between 1 and 5 volts or more, not sure. 1V is low, 5V is high and it should vary depending on the speed called for by the control unit inside the car. If this voltage varies then the regulator is probably bad. If doesn't vary then the control unit is probably bad.
Most of this is from memory so take it with a grain of salt and forgive me if I forgot anything.

PaulM

[Zulfiqar]

the test cable for the blower motor is behind the brake booster, to get to it you will need to peel the weatherstripping from the windshield and also unscrew the drain tray.

The aux fan low speed is wired through the ceramic resistor. It also has a tendency to burn the wires into a crisp. If they are then remove the headlamp to repair it. The fuses for the low and high speeds of the aux fans are in the panel that is behind the engine fuse box.

You will find two relays with fuses, one green and one blue, the green is high speed with the 30A fuse and the blue is low speed - originally it had a 15A fuse but was later updated to a 20A fuse, check those.

to trigger high speed aux fans at any time, simply unclip the wiring plug for it on the Tstat housing and the fans should run full speed.

If you are missing both speeds, test for voltage at the fan connector near the driver side headlamp, if you are missing voltage there then carefully check the resistor again. The high speed is also tightened on the output leg of the resistor. When the wiring burns there, you may sometimes lose high speed too.

btw - this car is of the crumbling wiring period of MB, make sure the wiring is clean.

for starters, clean the cabin temperature sensor in the interior next to the dome light. (blast from duster can). If you are stalled and scratching your head then pull the error codes from pin 7 of the diagnosis connector in the engine room.

[timmyr]

Paulhorner:

Same car, my blower motor is also stuck on Low.

Testing Procedure can be found in these two threads:
1)poor flow

2)blower regulator



connect a DVM to the appropriate wires, and then turn on the car and then proceed to run the blower on Low, AUTO, and High, observe the voltages for each speed.

My voltages were: LOW= 1v ; AUTO= 4.5v ; hIGH= 10.94V

next test, blower bench test: i "bench tested" the blower, by jumpering it directly to the battery and my toupee flew off. so i believe that the blower is ok.

blower current draw:
if u want, check out this thread, posts# 1-7 : Blower regulator or fan - help - W124

in my case, i was told that i need a new regulator by a reputable forum member.

good luck
tom

[timmyr]

Originally Posted by pawoSD

The regulator can fail, I've seen it happen before. On high/full speed the regulator is bypassed and full power goes to the blower. Could always look for a used or rebuilt regulator....

PawoSD: do you know of any places that sell rebuilt/refurbished regulators?

i know a local guy that repairs automobile electronics, but from what i've read online, supposedly the blower regulator is encapsulated in some sort of epoxy, which makes disassembly difficult . am not sure if this is true?

my local dealer wants $600 for a new regulator


thanks