Hi guys -

I have a 2003 MCS R53, roughly 86000 miles on it which I'm trying to sell. However, the AC doesn't work, and selling a car in the summer with no AC is not a winning proposition.

BUT - Here's my notes:

1) The AC blows hot
2) The dash button lights up fine. (on, solid, no blinking)
3) The coolant charge is fine. (3 cars done recently with with a 134a kit)
4) The compressor pulley is fine and running on a new belt.
5) The AC compressor Clutch does not spin when the AC is switched on.
6) Previously, I had a very loud fan running like a blender after the car was switched off. This was resolved with replacing the coolant reservoir (split seam on the back side) and refilling the coolant to the appropriate level.
7) I swapped the two relays that have the same # under the hood. no change.

I see threads about a low-speed fan, and a relay, and a compressor coil, and I'm assuming these are what I need to investigate.

Are there other things to look at first?

Where is the low-speed fan? Where is the high-speed fan? I only see the main radiator fan... which is that?

I assume the fan I used to get still running after the car was switched off was the high-speed?

Without the AC, Is there a way to test that both fans are working?

Is there a way to test that the compressor is getting electricity?

Thanks,
Tom

 

There is just one fan, it spins at two different speeds. The low speed should come on at 221deg, the high at 234 IIRC. If you have a scangauge or similar you can check to see if the fan is working.
From your description, odds are your AC clutch is out. You can replace the whole thing, or just the clutch - there are a few threads on that.

edit: here is the AC clutch thread
https://www.northamericanmotoring.co...-detailed.html

 

• Start car
• put on a/c
• Check for low speed fan - if it's not on 100% of the time with the a/c button lit up green, then your low speed fan is shot
• Have someone turn on / off a/c while you watch the compressor clutch. If it doesn't change, chances are the clutch (or the entire compressor) is shot.

A frequent failure mode seems to be that the low speed fan dies, and without the fan the a/c compressor clutch dies.....

 

NEW INFORMATION

So I just went under the hood, into the relay box, with paperclips, intending to jump the circuit and check the results. Then, after I burned myself I switched to a multimeter. HOWEVER... The burn told me that there was no power to the Air Conditioner relay socket, because I burned myself on the Fan II socket.

So, testing the switched circuit on the relay, I got 0 (zero) on the AC socket, while I got +/- 12 on the other three relay sockets.

All of this is jumping between 30 and 87, btw. (Those are the numbers on the relay blades)

Not knowing DC electrical, all that really tells me is something is different between that socket and the other three. My assumption from my AC (Alt Current) knowledge is that there's a break in the circuit for the AC (Air Conditioner) somewhere.

Since Fan II had an electrical charge, does that mean the standard resistor problem is not a problem? Basically, the resistor is fine?

Since the Air Conditioner socket had no electrical charge, I assume there's a break in that loop somewhere. What are my likely culprits?

Am I analyzing correctly? Or am I off base somewhere?

It feels good to learn something new about cars.

Thanks for any answers!

p.s. - Also, the car was off when this was attempted. My brain is suggesting the car should be on with the AC switch set on, and maybe I'll get a charge then... ?

 

Did you do the troubleshooting steps above?

I found that I got all kinds of strange results when testing with a multimeter, but the steps above will tell you what to do next.

 

The clutch does not engage.

Is the fan in question that little fan that's almost horizontal under the car?

 

Nope, the small fan is for your power steering. We're talking about the main radiator fan.

If you turn on your a/c and that doesn't spin constantly immediately, your fan resistor is shot.

 

Confirmed. The fan is not spinning.

Where is this irritating resistor?

 

The irritating resistor is integral to the fan, tucked into the upper right side (when looking at the engine) behind a piece of plastic.
But before confirming that the low speed is dead, make sure the the the AC is actually spinning when the AC button is on. You can look down on the left side of the engine and should be able to see the AC compressor spin when the AC button is on.
The definitive 'no low speed' determination is the 221deg coolant temp mentioned before. I replaced my fan assembly, but the low speed still didn't go on with the AC because the AC wasn't producing the pressure needed (8 bar/114PSI) to trigger the fan.
Replaced the compressor, now the low speed fan works when AC is on, and I get cold air - woo hoo!

 

Eric - The AC does not spin, ever.

The presumption (I assume), from John, is that the bad resistor stopped the fan, and the lack of fan caused the eventual clutch failure.

Am I understanding correctly?

AC switch is on, therefore the AC clutch runs, and the fan runs to blow on the condensor.

Here's an electrical question... if the switch is on, both the fan and clutch SHOULD run. Correct?

Any idea which triggers which? Does the switch itself trigger both? Or is there some series... like switch triggers clutch, clutch triggers fan.


Also, I see the Clutch repair thread... can anyone point to the resistor replacement post? I see the thread in the stickies, but with 28 pages, after an hour of reading I couldn't see any solution in there...