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#2056031 - 05/27/10 09:37 AM AC not working - compressor / relay questions
Bullwinkle Offline
n00b

Registered: 03/22/10
Posts: 23
Loc: OH
I have tried to search my way to a solution without any success.

1997 Crown Vic

My AC stopped working suddenly two days ago (of course its 90 outside right now). 7:00 it worked fine, 8:00 left work and noticed it wouldn't blow cold.

EATC problem, blend door problem ruled out.

Fuse is good. No obvious disconnected or damaged wires.

Compressor/clutch thing doesn't spin at all.

I swapped fuel pump and ac cutoff relays and car starts so I'm assuming the relay is good. I hear the relay click a little less than once per second with ac turned on, no clicks with ac button off. I've read, "jump the relay" but don't know how to do that. Again, I "think" the relay is ok, but don't know why it just click click clicks.

I've read to try jumping the pressure switch. Is that the sensor looking thing with the electrical connection that sits on a tube just forward of the accumulator? This is a common failure,right? Is it a difficult replacement?

I am leaning against low freon as it went from nice and cold to nothing in literally an hour. I also doubt the compressor failed just like that. Seems like electrical trouble, ijust don't know how to verify that the compressor has not indeed failed.

If I can somehow "fake" the compressor into engaging, does this prove its alright? I really know nothing about ac systems.
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#2056089 - 05/27/10 11:07 AM Re: AC not working - compressor / relay questions [Re: Bullwinkle]
Bullwinkle Offline
n00b

Registered: 03/22/10
Posts: 23
Loc: OH
Update!

Kept digging. Figured out how to jump the low side pressure switch or whatever its called. Clutch engaged, everything works nice. Blows cold.

Not sure what exactly that switch measures/does but I plan to swap it (its cheap and easy it looks like) and see how things go from there.

If this fixes the problem I feel like I couldn't be luckier! I'm just wondering if its possible that a low charge is responsible for this switch not letting things work properly. Guess I,ll find out soon...
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#2056111 - 05/27/10 11:28 AM Re: AC not working - compressor / relay questions [Re: Bullwinkle]
GoObYdOo Offline
Rookie

Registered: 04/20/10
Posts: 51
Loc: Fort Bragg,NC
Your system could have developed a leak as well,if you replace the pressure switch and it doesnt engage then you will need to have the system recharged,and they will also notice if you have any leaks when recharging it.
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92 Grand Marquis- heavy duty KYB Gas-A-Just shocks,the Addco bars are on the way!
"Only two things fall from the sky,bird s**t and Paratroopers,chicken s**t stays on the ground!"
"Show me a man that will jump out of plane and I will show you a man who will fight for his country"-Gen. James Gavin

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#2056119 - 05/27/10 11:42 AM Re: AC not working - compressor / relay questions [Re: GoObYdOo]
Bullwinkle Offline
n00b

Registered: 03/22/10
Posts: 23
Loc: OH
Thanks gooby.

Replaced the switch and everything seems good. I never would have dreamed I could fix it for $11 and didn't need a single tool! The shop wanted nearly $100 and my car all day to evacuate and fill the ac, and then pretty much a blank check if they had to troubleshoot from there!

Thank you to everyone that has ever posted here, what a great resource if you dig deep enough I think there's enough info to get anything troubleshot. Shooted. Sumpin like dat.

I love being a fledgling shadetree mechanic. It has saved me a ton of money this year. Probably over $3000 saved between 3 vehicles since january or so.
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#2056129 - 05/27/10 11:52 AM Re: AC not working - compressor / relay questions [Re: GoObYdOo]
Blue95 Offline
Over the Hill

Registered: 03/03/06
Posts: 2392
Loc: Past the Horizon
You did a great job checking things \:\)
That is the cycling switch, here's where it is on my 95


The purpose of this switch is to read the lo side pressure and cut the compressor off briefly in order to keep the evaporator core from freezing over. It is not uncommon to have to change it once in a while.

To check for a bad switch, yes you can jump the connector terminals but don't just leave it like that. This can cause high head pressure in the compressor = bad. The switch simply unscews off of a schraeder valve so all you should get is a slight puff of refrigerant.

Also check the connector - sometimes the wiring is bent down sharply by the hood and after many years can get a slight break. I had this issue on my 95. After replacing a switch and then having another problem I re-pinned the connector and all has been fine.

Very short cycling as you mentioned can be caused by low charge but this needs to be checked with gauges to be sure. Generally, the lo side pressure runs at 25-35 psi and the hi side runs 277-300 psi but can vary based on condition and outside temps. If you add refrigerant, do no add the r134a cans with oil or leak sealer. That's the wrong oil for these systems and the stopleak is like fix-a-flat inside the system, often plugs up the orifice tube and does nothing for a leak.
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2002 HPP-SOLD
badgeless grille-tinted tails-Hrbacek whiteface gauges-Pioneer spkrs-12" sub-reworked tranny internals-Sonnax/jmod upgrades-ceramic pads-urethane swaybar bushings-new timing chains/guides/tensioners-Granatelli plenum-75mmTB-MZT-NGKTR6 plugs-180d thermo-Steeda UD's-BOC 93tune-Thrush mufflers-LED interior/door puddle lights-Projector HID retrofit-MM corners-LED signal mirrors-17x8 TorqThrust wheels-235/55/17 Contental ExtremeContact DWS tires
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Current = 2011 Silverado, time for a change

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#2056254 - 05/27/10 02:31 PM Re: AC not working - compressor / relay questions [Re: Blue95]
GoObYdOo Offline
Rookie

Registered: 04/20/10
Posts: 51
Loc: Fort Bragg,NC
No problem!Being a shadetree mechanic is a lifesaver...especially on Air Conditioning as its usually very expensive to fix.
_________________________
92 Grand Marquis- heavy duty KYB Gas-A-Just shocks,the Addco bars are on the way!
"Only two things fall from the sky,bird s**t and Paratroopers,chicken s**t stays on the ground!"
"Show me a man that will jump out of plane and I will show you a man who will fight for his country"-Gen. James Gavin

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