I have a fairly old Coleman compressor unit I need to replace the contactor in..heres a pic of it :
http://i174.photobucket.com/albums/w110/sudave5/Picture001.jpg

Can you please give me a part number or style that I need to buy..thanks

according to your picture this is a 40 amp, 2 pole contactor. But the other piece of information you need is the coil voltage, which I can not see from this picture. The two yellow wires in your picture are going to the coil. Turn off the power, remove the contactor without removing the wires. See where the two yellow wires are going and read the numbers written in the center of those two yellow wires. Examples 24v or 120v or 208v

Since this is an air conditioner, and consumer I assume, in all likliness it has a 24 VAC coil.

This SC-E2-24VAC Products (http://web4.automationdirect.com/adc/Shopping/Catalog/Motor_Controls/Fuji_Contactors_-z-_Overloads/32_to_50_Amp/SC-E2-24VAC)

will work. It is 3 pole rather than 2 and it must be oriented 90 deg from what yours is. This might be why your contactor failed. Check dimensions.

A 40 A 2-pole contactor for AC units should be a very standard part.

Appreciate the info...it is a 24volt system...I went and picked up a newer cutler hammer version at the electrical supply today...thanks again.....let me ask this tho...since this unit is being fed by only a 30 amp breaker, shouldnt I match it with a 30 amp contactor ideally?..or will a 40 amp version work better?

Actually what you need to pay attention to is the horsepower rating of the contactor, not the resistive rating. This would be the sum of the condensor fan and the compressor. It needs to be greater than that at the very minimum. Oversizing increases reliability to a point where it is overkill.

The contactor must be HP rated for this application. I could find two 40 A contactors where only one was appropriate.

Note this page: Contactors - H2O Company Inc. (http://www.h2oco.com/online_catalog/catalog/g/g_4.htm)

where contactors are rated 40 amps resistive and 30 amps full load and just resistive.

Here is a datasheet for a contactor. http://www.gavazzionline.com/pdf/DPC-1Pole_v11.pdf Note the 40 A version is also for 30 full load amps. The 30 A rating is a motor rating and not a resistive rating like you might have for a heater.

Understood....thanks for taking the time to give me the info I was seeking...thanks again