Here's another "Who's the A/C expert" thread

rickbtbird

Registered User
95 SC with stock AC. It won't blow cold anymore.
The change was evacuated this spring prior to some minor engine related tear down. I put a quick charge on it today and it the clutch won't engage.

So.. I took it to a garage. They found a blown 10A fuse under the dash. OK not sure if that was related but, I felt like a jerk for not checking that. He was able to jump the lower pressure switch and the compressor engaged. He stated that after the fuse replacement they evacuated it again and recharged it. The compressor turned for 10 seconds and stopped. The system now has a brand new charge on it with no compressor engagement. I'm sort of disappointed that they didn't know not to charge without further testing it as that was for a cost. The consumer pays again, LOL!

He went on to say that they would have to rebuild the entire system to fix it as they don't have any way to further trouble shoot the system, at a cost of more then $1200.00. Not that I want to dispute their findings but, the system was fine prior to the discharge so how did all the components go bad at once?

Anyway I got a multi meter and an A/C manifold with hoses but I lack any troubleshoot skills. Maybe someone can guide me through this one step at a time?
 
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try replacing the low pressure switch,if you have a full charge this is what engages the compressor to run.is a cheap part around $8bucks.
 
try replacing the low pressure switch,if you have a full charge this is what engages the compressor to run.is a cheap part around $8bucks.

I got a MOTORCRAFT Part # YH552 called A/C Clutch Switch. Is this what you're talking about?
 
its called low pressure switch,screws into the dryer,the plug you said they cross over and the compressor came on,that plug -plugs into the LPS.
 
its called low pressure switch,screws into the dryer,the plug you said they cross over and the compressor came on,that plug -plugs into the LPS.

This would be much easier if you had a part number. I know what it looks like but I don't know how to order one without a P/N.
Is this the part you mentioned?
getimage.php
 
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Ok, offically I think it's called the A/C Clutch Switch.
  • FOUR SEASONS Part# 36494 $14.92
  • MOTORCRAFT Part# YH552 $20.89

Is the switch under pressure and do I need to drain the system prior to replacing that?
 
Help me understand this, If we are able to jumper the A/C Clutch Cycling Switch and the compressor comes on, we would want to replace that switch because it might not be sensing a signal from some other device?
 
Help me understand this, If we are able to jumper the A/C Clutch Cycling Switch and the compressor comes on, we would want to replace that switch because it might not be sensing a signal from some other device?

It may not be working, its supposed to come on at a certain pressure,
If its not "sensing" correctly it will never be able to tel when it is at pressure "X",
Thus the compressor is like holy crap i need to turn on NOW! or, meh....its all good dawg
 
It may not be working, its supposed to come on at a certain pressure,
If its not "sensing" correctly it will never be able to tel when it is at pressure "X",
Thus the compressor is like holy crap i need to turn on NOW! or, meh....its all good dawg

Thanks for the technical explanation:). Where's it getting the pressure reading from it it's not under pressure?
 
it is under pressure, but where it screws onto is just like a bike tire air valve.
holds air when you unscrew the switch, and it opens it when its tightened down
 
when you jump the plug in the compressor comes on right,that tells you it is working to the point of the low pressure switch.the compressor came on after they crossed it over,did they do this with a wire stuck in each prong on the plug in,eather way it came on.the LPS is eather bad or does not have enough charge on it you said it was recharged so the only thing is the low pressure switch,by the way i am certifed in auto ac repair.did theu vac the system to see if it held vac for at least 5 minutes befor recharging.did they leave it crossed over while charging.
 
it is under pressure, but where it screws onto is just like a bike tire air valve.
holds air when you unscrew the switch, and it opens it when its tightened down
Gotch ya! So I'll invest $20.00 at Autozone tomorrow for a new A/C Clutch Switch and test the system. Is there anything thing else I could do if that doesn't pan out?
 
tell them low pressure switch for the ac,make sure you make it clear to them it is for a SC,im sure it will fix your problem.to remove it ,use a plyers to loosten it then unscrew with your fingers,put it back on the same way get it finger tight then about a half turn with the plyers,make sure the new one has a o ring in the box with it.
 
tell them low pressure switch for the ac,make sure you make it clear to them it is for a SC,im sure it will fix your problem.to remove it ,use a plyers to loosten it then unscrew with your fingers,put it back on the same way get it finger tight then about a half turn with the plyers,make sure the new one has a o ring in the box with it.

I just checked Autozone on line and they have two listed for the SC but I'll make sure it's the correct one tomorrow when I go down there.
 
let me know how it works out,90 % of people come to the shop with ac problems think their compressor needs replacing,cross over the plug in it works,eather a bad lps or low on referigrant.
 
I just checked Autozone on line and they have two listed for the SC but I'll make sure it's the correct one tomorrow when I go down there.
Take the one that is correct for the year.. 134 runs better with a lower low side pressure. The r12 years will have a higher cutoff pressure... r12 = 25-30 psi, r134a = 18-25 psi, so their switches will have a slightly different range.

You CAN adjust either switch, but you sort of need a set of guages to do it. Otherwise, you can make small 1/4 turn adjustments and try it out to see if things improve or worsen. This of course assumes that the system is mostly full and free of leaks.
 
Take the one that is correct for the year.. 134 runs better with a lower low side pressure. The r12 years will have a higher cutoff pressure... r12 = 25-30 psi, r134a = 18-25 psi, so their switches will have a slightly different range.

You CAN adjust either switch, but you sort of need a set of guages to do it. Otherwise, you can make small 1/4 turn adjustments and try it out to see if things improve or worsen. This of course assumes that the system is mostly full and free of leaks.

Yup, everyone was right on the money. I got up at 6am and attached a multi meter to the clutch cycling switch and the circuit was open. I saw the screw and I removed the switch and tested it off the car while backing it off and I was able to get continuity so, I repositioned the screw back to home. I put it back on the car and backed off the screw until the circuit closed. I checked the charge with the manifold gage and it was a little low but not enough to give a dam. I picked up a new clutch cycling switch for 18.99 and slapped it on and it worked right out of the box. I topped of the charge, and the AC has been blowing at 43 degrees all morning. It's fixed!

Thanks for everything guys.
 
Glad that worked out for you Rick. FYI R12 cars and R134a cars use a different low pressure switch for 2 reasons #1 R12 and R134a cars work on slightly different pressures and more importantly #2 the switches for 89-93 cars have a different thread than 94-95 cars. They wont interchange. I always leave the early switch (if working properly) on cars I retrofit,never a problem. On 94-95 cars there is also a high pressure switch than can cause the compressure clutch not to engage, 89-93 cars dont have the switch. I love Ford A/C systems:( but I made a ton of money from them when I had the A/C shop:D.
 
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