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A/C issues in a NB1 Miata (compressor not engaging)

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A/C issues in a NB1 Miata (compressor not engaging)

 
Old 10-23-2018, 08:18 PM
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Question A/C issues in a NB1 Miata (compressor not engaging)

Hi everyone,

I am trying to retrofit A/C into my Miata and I'm having a heck of a time. I documented some other questions & issues I ran into in my prior thread. But I finally got it installed... however I cannot get the compressor to kick on.

I tried the following but got no where:
- Jumping the connector on the low pressure sensor (by the charcoal canister on the passenger side)
- Replaced the expansion valve in the cooling unit
- Swapping the A/C relays to check if one was bad (both could be bad I guess)

The only thing I have found that will engage the compressor is to directly hot wire the +12v lead on the compressor.

Any ideas on what the problem is? I was thinking it was the compressor but since I engage the compressor by hot wiring it, I don't think that's the issue.

Thanks!

Chris
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Old 10-23-2018, 08:54 PM
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Have you put a set of gauges on it yet?
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Old 10-23-2018, 09:17 PM
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have you filled up the system with freon?
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Old 10-23-2018, 10:05 PM
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Originally Posted by Erat View Post
Have you put a set of gauges on it yet?
Yep.

Originally Posted by borka View Post
have you filled up the system with freon?
I should back up. I have gauges & a vacuum pump so I hooked up the vacuum pump, verified no leaks after an hour. Then ran the pump for an hour and then attempted to fill it and got the majority of a 12oz can of R134a but there is still some in there... maybe 80% got in the system? So that's when I tried to hot wire stuff just to do some diagnostics.
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Old 10-24-2018, 05:41 AM
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What did the gauges read? What was the temperature when you put a can in?

You don't run the pump for an hour. Run for maybe 10-15 minutes and then let it sit for an hour. If you're still at -30 on the gauges there is no leaks.
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Old 10-24-2018, 08:51 PM
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Originally Posted by Erat View Post
What did the gauges read? What was the temperature when you put a can in?

You don't run the pump for an hour. Run for maybe 10-15 minutes and then let it sit for an hour. If you're still at -30 on the gauges there is no leaks.
I had forgotten what the gauges were last time so I just re-attempted w/ a brand new can of r134a and got 35 psi on the low (blue) side and about 22ish psi on the high (red) side.

I first ran the vacuum pump then shut it down and let it sit for an hour just to verify there were no leaks. Then I ran it for a full hour after I verified no leaks.

So in my re-attempt I did the following:
- Run vacuum pump for 30 minutes
- Shut down vacuum pump and verify no leaks after an hour of sitting w/ the pump off - confirmed... held vacuum
- Run vacuum pump for an hour
- Shut down vacuum pump and attach brand new can of r134a refrigerant to the feed (yellow) hose
- Use purge valve to ensure no air is caught in the yellow hose
- Open cold side port on manifold gauges

The reading after doing that was 35 psi low side / 22psi high side. I let that sit that way for about 20 minutes with no change. I then closed off all the ports and checked for leaks... no sign of leaks using UV dye, looking and listening, etc. Opened up the low side port w/ the can of refrigerant still attached and started the engine.

Starting the engine produced a gauge reading of 45 psi low side and 40 psi high side. The fans kicked on however the compressor refused to engage. Now I'm stumped.

Just for kicks, I weighed the can of r134a before I started and after I tried this. Before starting (full can with the tap attached) weighs 18.40oz. After my fill attempt, it still read 16.40oz. So refrigerant is not getting into the system for one reason or another that I cannot figure out why. Any idea?
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Old 10-24-2018, 09:07 PM
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If it's too cold outside, the refrigerant will be in liquid form in the bottom of the can. This won't allow it to go in. They say you can turn the can upside down and let it go in that way, but i don't recommend it. If you have a valve style can tap you can close it, bring the can inside and let it come back to a warmer temperature.

For R134a you should be seeing on the low side 35-45 high side when running 150-200. I think you have enough refrigerant in your system though. I would then refer to the expansion valve, but i think since you replaced it, it should be fine. I have an NB2 miata and the AC system is different from NB1, a little. If the pressure switch is working properly, you should be able to continuity check it.

I also don't recommend this, but when the AC fans kick on, can you jump the compressor to come on and also check pressures? If they come up, it could help induce the flow of freon throughout the system. If the fans come on (both) but the compressor doesn't engage, the problem could just be within that clutch circuit.
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Old 10-24-2018, 10:11 PM
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Ok I will try to bring the can inside & heat it up a bit. Should I re-pull a vacuum to try again or just heat up the can and retry?
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Old 10-25-2018, 12:02 AM
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I went ahead and heated the can in a pot of hot water and that DID it! I was able to get the system to suck down two 12oz cans and the compressor kicked over and would engage then disengage like it should. Temp was dropping in the cabin too. That's a great trick. Thank you so much!
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Old 10-25-2018, 05:57 AM
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No problem.
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Old 10-25-2018, 01:06 PM
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I often just set the 134 can on the exhaust heat shield or someplace warm like that while the engine is running and it is filling.
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Old 10-25-2018, 03:30 PM
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I usually just fill my wine chiller with hot water and dunk the 134a can in that while charging. Fits perfectly since it's already designed for bottles. Used to use a bowl of hot water but the can kept falling over and out of the bowl because of the shape.
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