My A/C Blows (hot air)

As some of you already know, the air conditioning on my '92 is no longer functioning. I bought the car recently, and the a/c worked perfectly when I did, but 2-3 weeks later it stopped blowing cold air. One theory is that it had a slow leak when I bought it, and the PO filled it up with r12 so it would work for potential buyers, knowing that it would leak out again over time.

We've established so far that the compressor is not engaging. Is there any way for me to tell if the system has leaked free of r12 vs. the compressor has failed? Or is there something else that could be the culprit?



I just realized that it stopped blowing cold air after I reassembled the dash after taking it apart to flock it, but everything else works (including the fan dial), so I would assume that I put it back together correctly.

Thanks! Any help would be appreciated.

If you are lucky, the PO recharged it with whatever freon and put a dye in there. Get/buy/borrow a black light, or the "special" AC light and goggles, and look for glowing spots on the AC parts. If you see some, fix that leak, vacuum/recharge, and go from there. You can usually see it without a light, but if it's slightly hidden you might not be able to without one.

The easiest way to check the compressor is to recharge the system to where it should be (and use a dye) and see what happens. It's not the proper way to do it at all, but it will tell you right away if the compressor is dead or not. But then you need to empty it all and start over again if you want to do it correctly.

Either way, there are some parts you need to replace when you open the system.

Basically, AC work sucks.

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Originally Posted by p4R4d0x

As some of you already know, the air conditioning on my '92 is no longer functioning. I bought the car recently, and the a/c worked perfectly when I did, but 2-3 weeks later it stopped blowing cold air. One theory is that it had a slow leak when I bought it, and the PO filled it up with r12 so it would work for potential buyers, knowing that it would leak out again over time.

We've established so far that the compressor is not engaging. Is there any way for me to tell if the system has leaked free of r12 vs. the compressor has failed? Or is there something else that could be the culprit?



I just realized that it stopped blowing cold air after I reassembled the dash after taking it apart to flock it, but everything else works (including the fan dial), so I would assume that I put it back together correctly.

Thanks! Any help would be appreciated.

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Check easy stuff first: Fuses, switch connections, etc. How much of the dash did you remove? Is there a independent switch pigtail just for the A/C button? I haven't been behind a Miata dash for a while.

If you are good with a voltmeter, chase wires and make sure the switch is sending a signal-> fuse-> relay-> clutch. Put gauges on the system (auto-chains will have these as loan-a-tools) while not running. Use google to find out what kind of static pressure a fully charged system should have.

Thanks so far guys - a lot of places to start. I've been swamped trying to get ready for midterms and then it's been raining, so I haven't gotten out there yet to snoop around, but anyway:

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Originally Posted by Rob®

If you are lucky, the PO recharged it with whatever freon and put a dye in there. [...] You can usually see it without a light, but if it's slightly hidden you might not be able to without one.

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If they didn't use any dye, will I be able to see anything without the light?

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Originally Posted by Rob®

The easiest way to check the compressor is to recharge the system to where it should be (and use a dye) and see what happens.

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If I don't see anything and nothing else pans out it looks like I'll be trying this.

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Originally Posted by Rob®

Basically, AC work sucks.

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So I'm realizing, hah.

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Originally Posted by boisking

Check easy stuff first: Fuses, switch connections, etc. How much of the dash did you remove? Is there a independent switch pigtail just for the A/C button?

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All of it :D It's a single plug for the A/C button and fan control, and the A/C button is connected (A/C lights up underneath the button when pushed). I checked the fuses under the hood and they're all fine, I'll have check the interior ones when I get a chance.

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Originally Posted by boisking

If you are good with a voltmeter, chase wires and make sure the switch is sending a signal-> fuse-> relay-> clutch. Put gauges on the system (auto-chains will have these as loan-a-tools) while not running.

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Not so good at wire-chasing, but I will have to look into the gauges if I can't find a leak.

My guess is low refrigerant level due to a leak. Kinda wonder if the PO did a R134A conversion. Without dye in the system you won't really be able to see a leak except for maybe some oil leakage in some parts of the system but you probably won't be able to find it.

All of the A/C work I know how to do has been self taught from simply doing the work and lots of reading and it was after learning lots of other things about vehicles.

Doing any A/C work without at least a basic set of A/C work gauges calibrated for the type of refrigerant you are using is like shooting at a target in the dark after you got spun around and got dizzy. It's not possible.

Honestly if I was you I'd just take it to a shop that does A/C work and get them to do it or if you want to come by here I can hook up my gauges (if it's had a 134A conversion) and I can at least check and see if there is any refrigerant in there.

Look for connections on the A/C lines for fitting that look like this

http://img43.imageshack.us/img43/6318/dsc06032.jpg

If it's a screw on type hook up then my gauges won't hook up to it.

Like jeepin said, if there is no dye in the system you won't be able to see much of anything, with or without a light. Unless there is a glaringly obvious break in the system (cracked hose, broken joint, etc), you kind of have to hook it up to some AC tools to track a leak down. If you rent a pump to put the system under vacuum (which you need to do before your final system charge), you could potentially find the leak that way, but that again really depends on where the leak is and how bad it is. Of course, if there even is a leak.

From the little I know of AC work (I'll be the first to admit that I know "just enough" about AC systems - but I recently had to replace every single AC component in my fiance's Cobalt and it's working beautifully, even in the 110°+ heat we were still having when it broke), I would put a set of gauges on it and see what the pressure is. Continue from there as needed.

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Originally Posted by jeepinbanditrider

My guess is low refrigerant level due to a leak. Kinda wonder if the PO did a R134A conversion.

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PO specifically mentioned that it had R12, so it would 'freeze your balls right off' or something of the sort. Otherwise I wouldn't have even made the connection that it might not have R134A. I didn't think anything of it at the time because the A/C was working.. Oops.

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Originally Posted by jeepinbanditrider

Honestly if I was you I'd just take it to a shop that does A/C work and get them to do it or if you want to come by here I can hook up my gauges (if it's had a 134A conversion) and I can at least check and see if there is any refrigerant in there.

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I looked quickly last night and didn't see any fittings (neither screw-on or quick-connect like the one you pictured). I don't get home until after the sun sets though, so I probably just missed them. I'd say I'll poke around this weekend, but with midterms next week I doubt I'll have a chance then either. Man, what was I thinking with this whole grad school thing :confused:

They are both right by the windshield washer fluid tank, near the very back of the intake manifold. One is about an inch above the other.

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Originally Posted by Rob®

They are both right by the windshield washer fluid tank, near the very back of the intake manifold. One is about an inch above the other.

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Yeah that would explain it, I was looking all around the compressor. Will check there - thanks!

Little late, but I just checked them this morning before heading to work, they're threaded fittings.. I have to get a crack in my headers welded when I get a chance, so I guess while I'm getting that done I'll have them check the A/C pressure, too, and update back here - thanks guys!