How to Fix your Car's AC System - Compressor Coil, Clutch Relay, Low and High Pressure Switches

In this video I will go over the electrical diagram of a basic AC System. Also diagnosis and testing procedures for your AC Compressor Clutch coil or stator, Low pressure switch, high pressure switch and your a/c compressor clutch relay.
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Disclaimer:
Due to factors beyond the control of Ratchetsand Wrenches, it cannot guarantee against unauthorized modifications of this information, or improper use of this information. Ratchetsand Wrenches assumes no liability for any property or personal damage that may arise from doing a repair on your vehicle after watching any of my repair video's. Due to factors beyond the control of Ratchetsand Wrenches, no information contained in this video shall create any express or implied warranty or guarantee of any particular result. Again Any injury, damage or loss that may result from improper use of tools, equipment, or the information contained in this video is the sole responsibility of the user and not Ratchetsand Wrenches.

[@adventurepoints7304]

Great explanation. Thanks for taking the time to make this video. Love the diagram and thorough explination

[@samnicholson1404]

This is such a great video, thanks for the information. Super easy to follow and no thing boring to have to wade through first.

[@mr.goodwrench6334]

Good drawing of A/C system !

[@Kaypee777]

Thank you so much for this! My Dad added coolant today and my car started blowing fuses and smoking and running horrible.. he ended up testing things out and jumped a wire to get the clutch to engage. (from the battery to the high pressure switch / wire) I am trying to learn what everything is called so I can explain this to my mechanic tomorrow!

[@corkyc6015]

Great explanation. I recently had 2- 4 cylinder cars come to me with erratic idle problems. Both were caused by bad cooling fans. THe cars ran great with the A/C in the off position - put the A/C on and the idle was all over the place. By the cooling fans failure, the A/C compressor would build up such high pressure, putting a big load on that little engine until the A/C high pressure switch opened to protect the system. Once the high pressure switch opened, idle would surge until the compressor kicked back on and idle would nosedive again. In this case, the high-pressure switch was doing exactly as you described-acting like a circuit breaker to protect the system.

[@geraldbowling2973]

You are good, very informative videos!

[@MrOmerta]

Thx for the info man. I finally fixed my ac on my 2004 crown Victoria since I got the car Jan 31st with heater worked but not ac but didn't check it during the winter.My problem was the high pressure switch. I bypassed the switch and my compressor finally kicked on added freon 2 cans now ac nice and cool.

[@blueridermg]

Love your channel bro. Good stuff thanks for all the 101

[@mikefeeley7599]

I agree with Mr. Ferraro, This gent actually teaches you something.

[@cavalierabouhamma2828]

It is very helpful, keeps on as always you did, thanks so much

[@eudeliafavella7234]

I love watching you, thanks for explaining everything your awesome and so much help.

[@markferraro5250]

great video you are one hell of a great teacher man keep em coming

[@myRatchets]

+Mark Ferraro glad you liked the video, stay tuned for more. Cheers

[@E.Khan04]

@@myRatchets Good day to you My car compressor still runs even ac is off. Can you help with this issue? Thanks

[@MrOmerta]

Thx !!! Man I fixed mine and so far here started to hit the hundreds 4 days okc . My problem was my high pressure switch on my 2004 crown Victoria. Now I can enjoy my ac finally since I got the car in jan31 with the ac not working. Thx !!! Good info video.

[@Stephen53886]

Thank you ! You've been very helpful .

[@israelcortez5643]

Thanks for your video very helpful. I have the same problem I didn't know what it was until that took it to the dealer they told me that it was a/c relay.

[@meyou991]

dude you rock I wish you lived in North Carolina you'd be my mechanic because of your videos I was able to diagnose down to two possible components did Stumpf Ford and several other places that a mobile mechanic was able to confirm in five minutes with his computer thanks man I appreciate it

[@GettinJunkDone]

Very clearly explained. Well done.

[@greywolff9367]

good video, now I have an understanding of a/c thanks

[@mangatsinghdeol2941]

Great video. Thank you for explaining it so well...million thanks...

[@thzzzzxxxx]

great video, its helpful, thanks

[@mojojojo911]

Hey. thanks for the video! appreciate your help.

[@shortridgegregory]

Outstanding, very helpful.

[@martinq1234]

Nice work on your video it is explained perfect.

[@seshachary5580]

great teaching. thank you.

[@stedy142]

Brilliant video! Thank you

[@nadarajahsivalingam2665]

Well done dude. keep it up.

[@jsilva7586]

great video clear and very informative

[@pathiragehenadira665]

Very useful video, thank you.

[@RickFisher]

Thanx! Very good tutorial.

[@tfossum11]

Great video on the fundamentals and failure points!

[@myRatchets]

+tfossum11 Glad you like the video, thanks for commenting.

[@daviddevries65]

Great video. Thanks

[@Peter-tf2uc]

Thank you, this is great!

[@johnmendoza6421]

Good explanation on AC system

[@ovi5961]

great video... good work..

[@fieldsofomagh]

Informative video on the theory and practice.

[@myRatchets]

+Tom OConnor Glad you like the video, thanks for commenting.

[@arefhashemi8079]

Perfect thanks for helpful video

[@meyou991]

hello everyone. I made a few posts here and wanted to share my results. 2010 f150. after Ford had it for 2-1/2 days and couldn't figure it out, I had a mobile mechanic come by. he plugged it into his computer and had a fault for evap temp sensor. 5 minutes it took. all pressures good. on this vehicle you have to by the whole evaporator box in order to get the sensor. so I bought one for a 2012 fusion, drilled a hole in the bix, inserted, attached a new pigtail and bingo. fixed. found out the next day I had no cool air, here the condenser pep boys put on had a leak, so I replaced it today, charged it and all seems great! 42 degrees out the vents. love this site, thanks a bunch

[@wyattoneable]

The best explanation of how the system works I've seen. Nice schematic too. :)

[@myRatchets]

+wyattoneable Glad you like the video, thanks for commenting.

[@djr3485]

Always something to learn on R&W's. Nice use of diagram to help explain the system.

[@myRatchets]

+DJ R Glad to hear you learned something, thanks for watching. cheers

[@jimmyhailey4019]

Ratchets And Wrenches will I be able to use ac gauges IF AC relay is bad?

[@sadiqmuhammadmaaji2932]

Thank you for sharing such knowledge... My ac compressor is not picking up at all. It's only blowing .. Had same issue a month ago.. Where I changed the relay.. But still having same problem now

[@greyhairedmountainbiker116]

Excellent video! I can't find a schematic and looking for HP switch. This video helps a lot. I think you got "high" and low mixed up on the car when locating switches

[@glennjones6004]

Finally, an ID on those dang pesky relays. This turned out to be the problem. Thanks.

[@tomr1961]

Great job. Question, Compressor not spinning. I checked the low pressure side and it was at 100 psi. Well in the red. What could this mean? Thanks again for a great and informative show.

[@ejazkhan2147]

sir wonderful lecture thank you

[@johnvu3132]

This guy knows his shit, good job, good review

[@minggthemerciless]

great video

[@buttishah]

Thanks for that great video .. my AC system goes off when engine revs over 4000 rpm what do you think the problem is?

[@Blksgrv]

thanks for the video

[@anti0918]

Thanks for the AC videos. Mine's been making noise when it turns on, and sounds like a bearing going bad.

[@myRatchets]

+brian0918 I have a video on how to check for and replace it, its more detailed than this. Just do a search in my channel. cheers

[@capriwoo]

Nice explaination

[@byrdman1057]

Hey thanks for the video, it’s useful information. I got a question, I’m working on my sisters car, and I notice when I connect the battery, with the car off, and ac controls off, you can hear the clutch engage. I’m thinking it maybe a stuck relay, any other places you suggest that I check? It’s a 2005 Accord

[@nothingfree3524]

pretty drawings nice colors but how do you fix the a.c ?

[@vonshango6311]

3:13 to test the high pressure switch, unlug it and use multimeter on two prongs for continuity. 5:25 when you dont have enough refrigerant, your compressor clutch wont engage.

[@fahdshaikh786]

Hey 👋🏼, great informative video . I have a strange problem in my Hyundai Sonata 2013 . The compressor turns on and cools really well , but sometimes the compressor won't just turn on for like 20-25 mins . I need to turn off the ignition and try again and sometimes if I'm lucky it'd start . Could you recommend what the problem could be ???

[@mardigras622]

Bravo!! Excellent description! Thank you.

[@donaldmurray4350]

again you are no moslem, but a splendid teacher, no less. .Content and entertainment are combined in reasonable proportions. For what you dear sir, or your channel, has saved me, I owe ya several cases of fine wine, or the good stuff, whatever. Once again I am genuinely grateful. I am almost 70, still working at a florida sand mine, & I cannot afford much, if any help. You're the man...who really helps. So...scag a hag, (navy lingo for forging ahead) dear sir.

[@hothifa2366]

Thanks for the detailed explanation. On my 1997 Camry V6, the clutch engages for 5 seconds before stopping (the AC switch button blinks after 5 seconds as well), filled the refrigerant, checked the relay, no issues. Is this a compressor issue?

[@switchbutt4U]

Hi . Great informative video. On my car VW Climatronic the ac and fan (low speed ) runs konstant no matter what settings. The only thing that shuts it off is when Climatronic is set to Econ (omic). That is normal cause it cut all supply power to Comp. and fan. The A/C works fine when cooling is needed so I do not think it is a coolant problem. I am suspecting a short in the low pressure sensor? Hope you can help.

[@robertmcclure184]

This is a very informative video. Thanks I have a question, I have a 1985 Toyota 4x4 Truck, The AC is cooling, but the compressor never cycles off. It never cools down very well. When you accelerate the engine the low pressure side drops, in the high-pressure side increases to about 250 psi. The high-pressure side normally sits at about 220. Because of the age of the truck I replaced the condenser evaporator, and expansion valve. I replace the condenser and evaporator, strictly due to age and the fins starting to come off. The compressor was replaced last year with an aftermarket compressor, as was expansion valve. I have now ordered from Toyota, a low pressure switch and a Toyota expansion valve. Would appreciate any ideas that you may have.

[@satish7759]

Heyy, I have Skoda Laura and problem is its AC not working.I got to know from mechanic that it's AC's Magnetic coil issue and to solve it we need to replace the full AC which seems very costly.Any thing from may gain my measures to reapir it at very cost.Hope that you'll help me

[@jamesflores9456]

the only vid recognizing the existence of the sensors ive seen

[@babyjjnels]

Great video. My ac compressor works but shuts off during hot 100 degree weather. How can I get it to stay on during hot weather?

[@Wes1988]

Great video I have a question my AC klutz continues to run I put a new AC compressor in and it is working blowing cold but the clutch does not cut off I look at the relay and the owner before tampered with the relay there is only two prongs on the relay with a electric wire going to two Prongs what could the issue be

[@lerch400block]

Great explanation sir. I've been in refrigeration for 14 years commercial and residential. I'm currently struggling with two of my vehicles. Beautiful diagram. I think I'm losing ground on the solenoid btw.

[@antoniop5889]

Did you figure it out. Think I’m having same issue

[@steve0o]

How do you test for continuity for the low pressure switch? I'm omhing out mine at the two terminals and I'm getting nothing. Although I do get a beep when on the positive terminal to ground. Does this mean I have a short?

[@THERIGGEDONE]

The AC clutch on my Honda CRV turns off while driving but works fine in idle. I have the correct amount of R134A, installed a new high pressure swich, and new receiver/dryer-bad relay perhaps?

[@rcasturi55]

You are great

[@chuckhollands7528]

I've noticed that in some of your videos, which I find very informative, you are wearing shirts with reference to San Diego. Do you live and work in San Diego? I live in El Cajon and would love to bring mu vehicle to your shop. What is your shop called?

[@rasheed4585]

hello where does the fan blower for cabin and thermostat fits in this diagram and also I dont see any interruption in the ac relay or clutch in relation with high and low pressure switches

[@hyderalitaj1]

could you tell us,how the blower motor and ac switch wired and related to the ac system?

[@Mientras_Tanto]

hello great videos! I'd like to ask, since you didn't mention, Is there another switches to tell fans to come on and off? o do they cicle on and off exactly as the ac compressor?

[@Mientras_Tanto]

I'm troubleshooting a 99 mercedes ml320, and ac comp engages but fans don't, so it blows warm air. no fuse,fans or relays problems

[@chucke3305]

Should i let air out of the hi side if its in the red using ac pro, the low side is in green range?

[@spelunkerd]

Just so I have it clear, minimum low pressure on the low side is necessary but not involved in compressor cycling on and off. The high side pressure switch is initially on, allowing the compressor to turn on, but when peak pressure is reach it cuts out. This shuts off current to the compressor clutch pulley, which then dislocates to allow the compressor clutch pulley to freewheel. So, the high side switch cutting in and out is what causes the compressor to cycle on and off. Correct? Are there thermal cutout switches as well?

[@myRatchets]

+spelunkerd Its the other way around, the low pressure switch does the cycling, the high pressure switch is for safety as far as I can tell on this setup, this way things don't go bust incase of a clog in the high side. No thermal cutout switches on this setup, but perhaps on the newer cars, not sure about that really. But alot of cars these days have sensor's that supply a varying signal voltage back to the pcm instead of just working like a circuit breaker like the two wire sensors in this video.

[@spelunkerd]

+RatchetsAnd Wrenches Oh, OK, that would work. The cutoff would be well above atmospheric pressure, cutting out when pressure drops below threshold, then cutting back in after enough gas makes it's way through the orifice tube/expansion valve to achieve low side pressure threshold. Then the compressor kicks back in and the cycle repeats. You've done a great job with this series, the best I've ever found on the 'net.

[@dnlmachine4287]

Both your guys videos are great. But I think R&R wins the racecar driver hair award lol. So dam slick!! Anyway I'm new to youtube publishing so If youre bored check my channel! Stay gold.

[@aboyad]

Hi, kindly i need your help with my AC system . the compressor clutch break and i replaced the whole compressor with new one , there was no dirt or shaving in the system , charged it and the reading are good high on 220 low on 30 but the problem is the air coming from the vent is about 65 to 70 which is way off . blender door is fine . the other thing the clutch wont disengaged . what could cause this problem please. thank you

[@bontly]

08 impala has a clutch always engaged. Even when the power plug is disconnected. Only blows warm air. checked and reinstalled all the fuses and checked the relays with a 12volt source. Has a 3 prong high pressure switch / transducer tested open. I unplugged it for a minute and the condenser fan reved up to high speed which it was not doing at all with it plugged in. Any ideas? thanks for the good info. I know I have to get the clutch checked out. But could there be an over pressure situation from it being engaged all the time?

[@TheOnlyRoute]

I was interested in buying a 2001 mazda protege but the ac is faulty . I was told it blows cold but works when it wants to, And that the resistors have failed on the grounding wires to the hvac system. Ac is important to me and wanted to how expensive would this b to fix wiring? Or should I just look for something else.

[@jwjsierra]

Ac stopped getting cold. Clutch engages, blend door works, condenser fan works, pressure gauge says too much freon which I know did not have too much in it...no lines are cold. Think it could be the high or low switches?

[@gotitallherellc9178]

Can you please tell me the number and location to the ac fuse and relay to a 2004 Ford F-150 5.4L xlt

[@knightrida6829]

thanks for your help I don,t know what the hell I,m doing !!

[@wettosixecho]

what would you recommend to start checking? My aunts highlander ac was working and it no longer switches on. Every time i try to switch on the ac button it doesnt light up, where it used to before.

[@fair2guy]

May be a moot point now, but for people watching- ive head the biggest problem here is just not having enough coolant in the system = low pressure switch will not engage, and allow power to the compressor clutch. Bad schrader valve stems are common sources of leakage. If you are working on your AC because it is empty, but a can of coolant with a gauge/hose, then check the low pressure port by connecting it and just tapping the trigger. This will allow the pressure of the low pressure line to enter the gauge and will show you if theres anything in it. If its empty, buy a $5 kit with replacement valves and the little tool and swap them out. Then charge the system a bit and maybe throw in some of that UV dye, and you may find a leak elsewhere.

[@fair2guy]

also- pressurizing the low side, even if its leaking, may tell confirm the low pressure switch is working by turning on the AC comp after it is pressurized.

[@nicksavage6350]

what symptoms would occur if the system had too much r134a? I have added to my system (using a gauge) after replacing all the components and am at the point where I feel I could be overcharging it. My compressor kicks on, then immediately off repeatedly.

[@collinroehner8920]

got a 2009 Nissan Altima, ac clutch wasn't turning, hooked up the refrigerant and the gauge read 150 psi, way in the read. Any thoughts?

[@dnlmachine4287]

2009 Subaru Impreza 2.5 non-turbo. This car came to my shop complaints of a hissing/whine. I havent tested anything except that removing the relay deactivates the A/C Clutch, but here is what I noticed: The A/C Clutch activates randomly when the Blower Fan is turned to any position. It has 0 (off), 1, 2, 3, 4, 5 Fan switch positions. The temperature setting, Recirculate button, and A/C on/off switch do not affect the Clutch randomly engaging at all. Basically, if the blower fan is turned on, the A/C clutch turns on and off at random - But it ALWAYS turns on if I switch the fan off, then on again. First thing I'm going to try is swap the A/C relay. With the A/C relay out, the A/C clutch does not engage at any time. If you good people have any tips to get me started off and save me a full circuit diagnosis I would be forever grateful! Stay gold.

[@Paradisepapa808]

its like watching the actor from ™everybody loves Ray" reaching in this video , but not as funny. And I'm sure Ray 's not this good at fixing A/C's . great video .

[@UphazZionPrincess]

Hi, I was wondering if you can help me figure out what is wrong with the heater in my car. while I'm driving it tends to turn on by itself and shut off. It also changes where heat is blowing from. This just randomly happens but not always. Any idea?

[@tylerluc7328]

thank you for the informative video on the AC system. Is there an AC shop in the L.A. area you would recommend?

[@mastermind6542]

Did you find one?

[@joselitoyara4336]

I would like to ask you a question and hoping that you will help me with my ac problem on my mazda bongo friendee dual aircon van. When I engaged the front ac blower, the clutch motor does not shut off/on automatically. It runs continously and that caused draining the battery, so i disconnected ac front blower and only back or passenger's aircondition will run clutch normally. What should I do? I hope that I can fix it with your help before I go to the professionals if needed. Thanks and hope that you''ll help me on it.

[@zayalhawa1062]

Dear RNW you are great and you take your time to explain things well. But I have Question about my system which is confusing and I have not seen solution to it on you tube Maybe you can Help. I have Tundra 2001 it had front right side body damage affected the fender, RF headlight and air filter housing and bent the condenser, also replaced the Radiator, and fan was broken also. All were fixed. System had pressure even after accident. First situation was Low pressure low (15-20), and High pressure High over 250psi, and clutch engage and disengage frequently we added Freon just a little high side went way up and low stayed the same, pursuant to Toyota Diagnostic table, indicated Blockage in the Receiver Dryer or expansion valve, we replaced both, we also tested all the line connection for leak, after replacement and testing condenser for leak we got to situation 2. Now the condenser have minor bent but holding pressure, the low is steady normal at 40 psi, and the high side went too high 275 and kept increasing to about to 350- to 375 close to 400psi and we did not even put one small can and clutch engages all the time without stop. Do you suspect the high pressure sensor not closing the circuit and causing all of the issues?

[@williamhough33]

My ac is not staying engaged on all the fan selector settings. The A/C light stays on and unit engaged on setting 1 without issue but settings 2,3,&4 are intermittent or not coming on at all. Does this sound like a bad A/C control relay connector? I changed the fan blower switch thinking it may be bad as I was advised by a friend but I did not see any bad contact points or burn marks on it. Thanks!

[@MrAmrit90]

Thanks i check my relays are fused if i bypass the socket then ac fan and compressorstart automatically if i on the key so i have to change relay

[@williamvelasquez825]

I basically have the problem my ac doesn't engage but when I add power to it it does so should I just changed out my relay or rewire it and add a new relay ?

[@luisvargas4577]

I am adding freon on the low side but the refrigirant seems like its not going into the system. How long does it take to empty the can and get the clutch to engage? at what pressure on the low side does the clutch engage. I was adding the r134 for about 20min but the can seems full the whole time.. Am I suppose to let run for longer and i do turn the can upside down. I have a manifold set and I vacuumed the system already

[@thephilosopher4719]

Good day, Where is the AC Comp Relay located on a Hyundai Elantra 2014? As, when the negative side of the battery is disconnected, and the lead touches the battery i hear a clicking sound near the compressor side, and the parasitic draw jump to 2 A and i believe it is the cause of my dead battery in the morning! Please help!

[@TheMetramex1]

hi, i would like to ask you a question, when i turn on the AC in my mercedes clk it works for 2 minutes and then the compressor stops. i checked the voltage it drops to 9,6 volt, any idea? thanks

[@RickFisher]

The compressor is failing. If you get it changed now you might get away with just the compressor but if you wait until it finishes grinding itself up you'll need a complete overhaul!

[@Lucky---]

Great video. What should i do when A/C relay terminal 85 has no continuity but the fuse is good? Thanks

[@techs8660]

Use a different relay from a working system and check if it is a relay issue.

[@Ummaah]

I need an answer regarding the wiring system.... is there all the cars has same wirings or its differ from one another.... Please elaborate🙏

[@davidaguayo3785]

I check petty much the electrical system found that the connection to the compressor does not have electricity going to it what you suggest.

[@Uae_ksa_]

Hi bro thank you for the video it helps alot but I have a problem with my 2009 Toyota land cruiser vxr , the AC after many one or two hours driving the car , it starts to disconnect and reconnect , it keeps blinking connecting and disconnecting so I was afraid this will cause more damage to my car Ac so I stopped the compressor and only using only Fan , what do you think is the problem? Thank you for your time

[@cayugafutures]

My AC compressor clutch is always ON. I checked and I am always getting voltage to it, regardless if my interior switches are OFF. HELP!!!!

[@dee1380]

I have a 1989 Lincoln Town Car that has been a nightmare on A/C issues. My A/C shuts off on the highway, my fan shuts off when I select floor, & nothing comes out my defrost vent when I select defrost. Could my low pressure switch be failing? I just changed my check valve & Automatic Temperature Control Switch Servo. There was no change. Changed my blower motor resistor a couple years ago, so it's not that. I'm out of options. Do u have any idea what the problem may be? Thanks in advance.