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AC compressor not engaging

26954 Views 13 Replies 6 Participants Last post by  Cusser
First world problems, right? AC not working in winter? It was working fine a few days ago (isn't everything that breaks working fine?) No signs of anything bad happening, no squeals, no smells, nothing. I recently moved back to Colorado from being in Vegas, so I'm thinking it didn't like the trip. It is a 2007 frontier with 105k miles.

I can cycle through all the speed settings on the blower just fine. AC light comes on but I can't feel or hear the compressor engage. I checked the fuse under the hood and it was good (10 amp fuse). I checked for code and there's nothing, no pending and no stored codes.

I didn't smell anything when I was down there with the engine off and with it on with the AC on. I didn't see any fluids or anything.

Now, when I was in Vegas I dont know if it was the heat or what, but the AC would be cold, but not THAT cold. Say it was 110 outside, the inside of the cab would be 85. Maybe 80. Could I just need a recharge? I was under the impression the AC system was sealed and the only time a recharge is necessary is when there's a leak.
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I'd get the free loaner gauge set from Autozone, and measure the R134a pressure. I'm thinking that you just had some normal R134a attrition over the years (the system is designed to leak a tiny bit at the compressor seal, to keep that lubricated), and now your system is too low to actuate the compressor, for safety. Your comment on the below-standard cooling prior to this seems to corroborate this. My experience with my '98 and 2004 Frontier AC systems in Arizona is that they perform GREAT.

My 2004 Frontier just needed - for the very first time this summer - R134a top up. Remember - NEVER add any sealer or refrigerant containing sealer. UV dye is OK to add though.
I'll just take it to a shop and have them top it off. We have a guy here my family uses that does honest work.

So the AC system is actually designed to leak a tiny amount?
YES. BUT may take over a decade or more to have enough leakage for a noticeable drop in AC performance. Otherwise the steel compressor shaft would burn/degrade the seal and the leak would become large. Same for an old VW flywheel seal, a water pump seal, etc.

No, the system should never leak anything. If you lost refrigerant, you have a leak.
Maybe you should've had a V8.. Because you're just plain wrong here.
I was under the impression that if you're refilling the A/C the compressor needs to run in order to circulate what's being put in. That's why I'm curious about engaging it. Or am I wrong and the compressor doesn't need to be running?
When one has an empty system just containing refrigeration oil/dye like after a repair, a good vacuum is pulled for at least 30 minutes to remove moisture, remove air, and that vacuum will allow refrigerant to be pulled in without the engine and AC being on. After that stops pulling, then the engine and AC are switched on and the remaining amount of refrigerant added.

A system that is low enough that the compressor will not engage will usually accept refrigerant directly from the can without jumping the compressor, just from warming the can with your hands or warm water.

A shop has an electronic machine to add all the refrigerant at one time by weight after the vacuum step, faster and more accurate.
1. Get real set of service gauges.
2. Replace the AC relay.
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