I suspect most 'automotive' relays are not rated for 120vac operation and unless they were I wouldn't use them as such. I was just responding to the statement:
From what I have seen about relay specs, the contacts are rated for both AC and DC - generally for AC, you get a higher current allowance on the contacts than you do for DC (and generally the DC is at a much lower voltage). I think part of it has to do with arc-over possibility from DC vs AC (which is alternating thru a 0 volt area, and thus the arc-over is less likely). That isn't to say that all DC relays could be used for AC - but there is a strong chance that a good quality DC relay will work fine for AC switching.
My wife works as a barista at a combo coffee and ice-cream shop, and her boss is cheap. I get to play "appliance repairman" on occasion, because her boss buys second-hand commercial units that have no service contracts or such, and cost an arm-and-a-leg to have serviced or repaired - or cost twice that amount to buy new. One day, my wife came home with the business' waffle cone maker. This is essentially a waffle maker that has two griddles, you put some batter in, close it, hit a button, it counts down and you have a waffle made that is rolled into a cone, cooled - and there you have something to put your ice cream in.
It was broken - wasn't heating up at all. I took it apart, and saw that there was a small micro-controller unit hooked up to the LED countdown system, plus a bit of circuitry connected via wires to a transformer that converted the AC coming into the box to 12 VAC, which was then rectified on the microcontroller board, and probably ultimately turned into 5 volts for the controller. Other wires left the board and went into a relay, which I could see had the AC wires across it that went to the heating coils of the griddles. So - the controller heats it up, and regulates the temperature of the griddle by switching it on and off (there was also a temperature sensor in there as well - probably a thermocouple of some sort).
I could see that the relay was dead burnt out (it was literally charred). The company that made the griddle wanted about $800.00 to repair this machine. This thing didn't even have $100.00 in parts or labor in (talk about making a killing - man, manufacture commercial cooking equipment, and you're set for life!). So - to repair it, all I needed was a relay...
Well - it was a 12VDC Omron relay - I looked it up, it needed 20A contacts. Since it was late-evening, nothing was open to buy parts from (Fry's Electronics was already closed), so I figured, what the heck - a cheap Bosch relay from AutoZone should work. I went down there, and picked up a 40A unit meant for switching something or another (blister pack special for auxilary usage). It had a screw mount, which was perfect because the original Omron relay was screwed to the sheet metal chassis of the waffle cone maker. I got it all hooked back up, we turned it on - and the thing heated up just like it was made to!
We ended up taking it back to the shop that night, and ran a batch of waffle mix through it to make more cones (well, in this case, it was a bunch of waffle bowls). It made them perfectly.
A few days later, my wife brought me a hundred bucks from her boss, and her boss was really grateful. That was several months back; that machine gets used every day, and it still works great. That relay will probably outlast the machine (even so, her boss only got the 5-5 warranty from me - 5 minutes or 5 cones, whichever comes first).
Anecdotal, sure - I wouldn't trust such a fix to get me to the moon or something - but at the same time, it was cheaper than the other option (and faster than getting the Omron replacement relay, which I did find on DigiKey, and it wasn't that expensive - but the business needed the machine working -today-, not a week or more later)...