I was having issues controlling the temperature of the car so I purchased a replacement Climate Control unit for my 2003 V40. I got the same part number and it was a newer part - must have been a replacement. Now that Summer is here, it may run cold for a few minutes and then cool and then warm. I had it all checked out at the local non dealer shop. No different. I then put the original unit back in the car and it runs the same. I even have it set to max cold and fan set to max. Something is overriding my desire for cold air. How to I override this and make it completely manual - just max cold or max hot and I will control with the fan speed and vent openings? Do I buy a manual unit off ebay - would that work?

You cannot swap in a manual CC unit, forget that idea.

Have you checked out the compressor clutch? Listen carefully for the clutch when it starts to warm up. You should be just able to see the clutch end of the compressor under the hood and determine if it is actually working.
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My back feels better when I sit in a Volvo seat

how difficult is it to replace the clutch? Any special tools required?

If the clutch is no longer engaging once the compressor gets warmed up, you could try shimming the clutch from the outside. The S60 cannot use plastic 'bread clips', but you can make metal shims to glue into place.

Do a search on clutch shims or bread clips. This is a 15 min DIY fix that can last a few years.

The 'proper' way is to remove the clutch from the compressor, and move the shims from the rear of the shaft to the front of the shaft. This will take a good mechanic a couple of hours... There just isn't much room under the car.
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My back feels better when I sit in a Volvo seat

well - you are correct - it is the clutch unit. I put in shims and they worked (I only tested for a few minutes) and then I glued them in. Now it is worse than before. Don't know if I need bigger shims and smaller. Will work on it in the morning after it cools down. I used plastic shims. I may insert metal washers or try cutting off pieces of feeler gauge.

Plastic won't work for your particular clutch. I used sheet metal, folded to the correct thickness, and glued them in. They must all be the same thickness!

I suspect that one of your shims may have fallen out. It takes a while for the glue to set...
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My back feels better when I sit in a Volvo seat

We just went through a similar scenario with our 2000 V70. Bread clips didn't work so well and I bought 2.5 hours of labor at the local Indy shop to reshim the clutch. Money very well spent, stays cold inside the cabin at 110 degrees F ambient temp.

I don't know if the S40 AC compressor/clutch is of the same design though.