My 99 v70xc keeps burning out air conditioning compressor relays. Replaced relay and a/c blows cold for about 20 minutes then relay dies.

 

relays can burn out when too much current is going through them. Since the compressor clutch is really a big electro-magnet, I'd suspect its drawing too much current and overheating the relay.

 

I agree, but I will also just ask are you sure the relays are bad? Are you testing them?

 

Haven't tested relays. A/C runs for about 20 minutes then shuts down. Relay is very hot to the touch. A/C wont come on at all after that until I replace relay.

 

Perhaps the compressor clutch is on its way out. Measure the gap, it can be adjusted if too large (maybe that is what is making the clutch 'work too hard' although I don't know if that's possible, usually the clutch just doesn't engage, but the relay doesn't die as a result).

 

+1 on the clutch gap. should be about .3 MM. When the gap gets too large say .7 or .8MM the clutch heats up, the magnet loses its ability to grip, the impedance drops (drawing more current), finally the clutch releases until it cools off. If you can get access to the clutch (not easy on all models) you may be able to remove the pulley and reshim without opening the system. Should be vids on Youtube

 

That is a universal problem with this particular compressor, but of course they start working again when they cool down. It sounds like that is not the case here.

 

On my C70 recently, the clutch just stopped engaging from one day to the next, and it would no longer come on, cold or hot. I took off the clutch disc using a loaner compressor clutch removal tool from Advance Auto, and removed one of the shims underneath the disc to narrow the gap back to spec (it was at .7 mm). The AC now works again fine, and I didn't have to replace the relay or anything. I also topped off the freon in the system using one of those cans-with-a-gauge, as that was also a bit on the low side which can be another reason the AC no longer works. On the C70 the clutch is easily accessible behind the passenger side front wheel well.

 

Easily is certainly not a word I would use on the V70.