Automotive Air Conditioning Information Forum (Archives)

John_MS on Wed June 25, 2014 10:48 AM

Year: 1990
Make: Nissan
Model: 300ZX
Engine Size: 6 cyl
Refrigerant Type: R134
Ambient Temp: 85
Pressure Low: 25 PSI
Pressure High: N/A
Country of Origin: United States

Hey Guys. First a little background on what my initial problem was and what I've done so far.

A/C was working fine. Let the car sit for a few weeks without running. Take it for a spin and no A/C. Try to charge with R134a. Hear a hissing sound around the compressor. Pull compressor, replace dry rotted O-rings, pressure release valve and dryer(all R134 compatible). Install 7oz new pag 46(per manufacturer specs). Vacuum down system and shoot a bit of a charge while car off just to verify no leaks. All is good. Start the car and of course the clutch does not engage until I shoot about ~15psi of refrigerant. Clutch clicks and I can see it is spinning. Fuse is good.

Here's the problem. Just as my can of A/C Pro reaches the green area(25psi) the clutch fuse blows. I release some pressure from high side port and repeat the cycle with the same result. I'm guessing about 6oz of refrigerant is in the system at the time the fuse pops. It is supposed to hold 23oz.

Where should I start my diagnostics?
My first attempt at A/C repair. Thanks!

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2007 Nissan Frontier Nissmo

1990 300ZX Twin Turbo

Dougflas on Wed June 25, 2014 11:59 AM

First place to start is to stop using AC Pro. You need a set a real gauges with a high and low side guage. Make sure you're not getting liquid into the compressor or you'll be replacing that again. Put the proper charge in the system by weighing the charge amount.

John_MS on Wed June 25, 2014 12:25 PM

A/C Pro can is 20oz. My system should hold the entire can, right? The A/C doesn't even show any sign of cooling the vent air before the fuse pops. I squeeze the trigger for a couple of seconds and check the vents. Repeat.

I do have a real set of gauges. I guess I'll measure the high/low side pressures and see if anything odd is going on. I'm leaning towards the magnetic clutch actuator going bad. But I can't figure why it works until I start to charge the system.

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2007 Nissan Frontier Nissmo

1990 300ZX Twin Turbo

AC_Doc on Wed June 25, 2014 1:06 PM

Sounds more like when the low side reached 25 psi is when the pressure switch energized the clutch coil and the fuse blew due to a current overload. I'd be checking the coil wire connectors and the wiring back to the firewall for a pinch that's grounding the wiring. Pretty unlikely the charge amount is responsible for blowing the coil fuse.


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Sometimes you must accept things at faith value!

mk378 on Wed June 25, 2014 8:26 PM

The fuse doesn't have anything to do with the amount of refrigerant. Something is drawing too much current. It will do that whether the system is empty, normal, or overfull.

Resistance of the clutch coil should be more than 3 ohms (which would draw 4 amps at 12 volts.) If the coil is partly shorted, fuse will blow.

The condenser fan may be on the same fuse. With the key off, try turning the condenser fan by hand. If the bearings are bad the motor will draw too much current and blow the fuse.

Jag987 on Wed June 25, 2014 9:12 PM

First, welcome to the forum. Second, read my signature line and change "expert" to "pro", that is what you have in your hand. Next, if you decide to continue to use the death kit you have, and your system call for more than what is in the can, why are you just squeezing the trigger for a few seconds then checking the vent temp? It will not cool much until the system is almost full. Second to last line in your first post says you have a real set of gauges, attach those to the car and hook the death kit can up to them to charge it the rest of the way.

As far as the fuse blowing, I think some good advice has been given on things to check.

Good luck!

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I bought a can of 134a at w**-mart that had a stop leak, oil, and dye in it. It also had a hose and a gauge, so now I'm an AC pro!

Dougflas on Wed June 25, 2014 10:51 PM

Jag,
I don't think he can connect the AC Pro to the manifold gauges.

Jag987 on Wed June 25, 2014 11:14 PM

There is another thread where someone did. They unscrewed the hose/gauge from the top and screwed on a can tap. At least that was the claim.

Edited to add:

This thread about 5 posts down. It does not say it was a/c pro, but same setup.

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I bought a can of 134a at w**-mart that had a stop leak, oil, and dye in it. It also had a hose and a gauge, so now I'm an AC pro!

Edited: Wed June 25, 2014 at 11:33 PM by Jag987

John_MS on Thu June 26, 2014 8:00 AM

Thanks for the advice guys. I ohm checked it(one probe on coil wire, other on ground) and only got .5 ohms. Looking bad. I'll follow up when I get it fixed.

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2007 Nissan Frontier Nissmo

1990 300ZX Twin Turbo

Edited: Thu June 26, 2014 at 8:18 AM by John_MS