Diagnosing a vehicle's A/C system: Low side PSI is High & the High side PSI Low

Learn the 4 main conditions that will cause your vehicle's A/C pressure to have low side pressure that is high and high side pressure that is low. Variable displacement compressor diagnosis is also covered.

[@michelcarballomendez]

Gracias profesor por este video, vivo en Venezuela y tengo una mazda bt50 que cuando está estacionada, el ac no enfría, pero cuando salgo a la autopista funciona perfecto. Creo que esta mal mi fan clutch. Gracias profesor

[@pixeldennis2862]

Thanks I hope you’re still around … Dealing with a 2011 Jeep compass . The low reads hifh and high a little low . I’ve seen many people having issues with these cars and people mention the tool you’re using to adjust the duty cycle … I’m hoping it’s my txv or overcharge … It was properly evacuated, held vaccum passed leak test and proper ref was replaced . The readings after this was apparently normal readings . However later on the pressures flipped again .

[@pixeldennis2862]

What’s this scan tool and what are the electrical systems I need to check?

[@victorcalderon007]

Can you say; get to the chopper

[@dfwbabydriver]

😂😂😂😂

[@pariah7843]

I like the way he talks. It’s adoribole

[@RogerPack]

I think mine having very lsome weird readings once...fixing the idle improved things a little... at least better while idling :)

[@JordanFritzsche]

Awesome video, thank you!

[@caiobabe]

Excellent video. TY

[@michaelboibodas]

Hi. Just changed entire AC system(compressor, expansion valve, O-Rings, Condenser, and Schrader valves. On a Honda Accord 2.4 Liter. I vacuumed system out. Purged the yellow line of air, between Freon cans. The Low side reads 25 psi BUT THE HIGH SIDE READS 110-112!! Ambient outside temp was 65-70 dry conditions in AZ. What do the readings mean? I put a thermostat inside the car’s vents and temp read 40f! It was Ice Cold. Did I do everything correctly? Why is the high side not at 150-175psi?

[@ProfessorPentane]

Hi Michael, You caught me at a good time as I do not have time to respond to all of the questions from my KZbin videos. Your gauge readings could be normal for a milder 70F dry day with. Was the engine at full operating temp? That will cause the reading to be lower if the engine is not hot. Try switching to the fresh air mode to see if the extra heat load will raise the high side pressure a bit. But I think over 150 on a mild day is normal if you are blowing out 40F. You will not know for sure until it gets nice and hot in AZ. Thanks for watching, P.P.

[@timsigley5806]

Great to point information i was looking for thanks alot. I subscribed and liked channel

[@DragonRoyZ]

I just replaced my AC Belt, previously it was always going 40psi on the low pressure port as the lowest. After I changed It, I now get 30psi easily. What is the effect of the new AC Belt?

[@ProfessorPentane]

The old belt could have been slipping causing the compressor to be spinning at a slower speed. Thanks for watching.

[@AncapistanVan]

Thank you sir. Great video

[@ProfessorPentane]

My pleasure

[@HK-qj4im]

Ok. Now I know.👍 very helpful.

[@Az56818]

2011 highlander new compressor expansion valve condenser charged to proper level using robinair machine ac compressor and fans only stay on above 1k rpm

[@RomeB-qe4mf]

Are you measuring voltage to the solenoid on the compressor=duty cycle? (ie 4V = 40% duty cycle)

[@ericforest9186]

How can we check for an electrical problem? I checked all of the fuses. Can I somehow put 12v to the compressor to force it to run?

[@ProfessorPentane]

You can put 12 volts to the clutch but not to the variable displacement solenoid.

[@ShakotanRon]

I’ve got a v.d. compressor in my 2003 x5. I’m experiencing only 1 to 3 psi change between high and low with the clutch activated. Classic symptom of a bad compressor. Pressure was around 100psi static, and I believe it was 85+* outside. My question: is it possible for this to happen by a stuck open expansion valve, and or a low duty cycle, or stuck solenoid?

[@ProfessorPentane]

A stuck open expansion valve would have a greater change than 1 to 3 psi, not the problem. It looks the compressor is not pumping at all with those pressure readings. Yes, it could be a solenoid problem, but hard to tell if you do not have the special tools to check. Most DYI guys will replace the entire compressor for this problem, but remember, it could an electrical problem that is causing the computer to not turn on the compressor. Also check for fault coeds. I would diagnose this problem by looking at scan tool data and use a special tool to bypass solenoid and manually control the solenoid. Again, hard to diagnose without special tools. Good luck. Does this compressor have a clutch, is it on?

[@phillippardo5712]

What if ac blows cold on highway, couldn't still be a stuck open txv? And wouldn't a stuck open txv cause the gauges to not equalize when turned off?

[@Nes_2k]

Make sure fans are working properly

[@alano2875]

Thanks for the video. I'm diagnosing a problem with my AC. 1999 Chevy S10 Blazer. Compressor does short on/off cycles continuously. 3 seconds on 3 seconds off over and over. System is clutched fixed displacement compressor, condenser, orifice tube, evaporator, accumulator dryer with low pressure switch. I don't see any high pressure switch anyplace... 70F air outside. Low side looks like about 100 psi. High side goes from 75 psi (compressor off) to 100 psi compressor running). I suspect low pressure switch on the accumulator is bad. Cheap and easy to replace... Should I jump the low pressure switch to see if the compressor is able to build more pressure and bring low side pressure down before wasting time swapping low pressure switch.

[@highwayman1218]

Whats the gauges say system off on freon charge? The constant cycling sounds like low freon. The PSI readings you do have sounds like a bad compressor. Its a pump, KISS principle. High low side means its not sucking. Low high side means its not pushing. Nothing else is going to cause those psi readings. Simple system and compressor failure is common on those. Just fyi, the high side switch is located on rear of compressor. I personally would check the gauges for freon charge. You can bypass the low switch for a short time to check psi if you cant judge freon charge with gauges. It sounds like you have both low charge and bad compressor. The low psi switch Id have last on your list, they're reliable. I would plan on a compressor, condensor, orifice tube, accumulator and flush in your future personally. Id also suggest checking the fan clutch for operation at idle, they go bad and eventually kill the compressor with excessive high side psi in the heat.

[@alano2875]

Thanks! Charge is not low. Probably bad compressor. I have a new compressor...plus orifice o-rings, oil. Looking for local place to recover my refrigerant...then I'll flush condenser replace the compressor and put it in vacuum. Unfortunately WA stores don't sell R134a...so I'll have to pay someone to recharge (or drive down to Oregon to pick up some R134a)... Probably cheaper to pay for recharge than drive 350 miles round trip.... P.S.: I've never been able to locate the high pressure switch...but would like to replace that at the same time.

[@highwayman1218]

@@alano2875 Be sure to replace accumulator also. Weird, on the switch. I wonder if the high psi switch is broken off? Should be on rear of compressor and held in with a c clip. OEM AC Delco compressors will come with a new switch, aftermarket youll need to reuse the old one. Theres a port on the back with a plug. Wow even in wacko CA we can buy R134 at the parts store. Crazy in WA, you cant.

[@alano2875]

Thanks. That's part of the UAC kit I picked up.

[@alano2875]

Found the switch...right where you said. Will source a new one for new compressor...as you said...plugged and not included. Summer will be over by the time I get to fixing this... If the compressor goes...how common will a plugged condenser be, I wonder...guess I won't know until I get there... Thanks again!

[@BallisticBen247]

Hello!!! I'm watching this and I can't see my issue. Please help! Details below. What it is: 2004 Dodge Ram 1500 5.7 v8 I changed out shipping pag in ac with new pag46 3 oz in compressor (2 oz reg. 1 oz uv After replacing everything, I vacuumed system for 2 hours vacuum held Added 3 oz pag 46 (2 oz reg. 1 oz uv) system requires 6 oz. Started truck No clutch engagement Added 1-12oz can r134 to Low side (requires 22 oz.) No clutch engagement Added other 10 oz No clutch engagement Jumped 30 to 87 on relay to engage clutch New stuff: Ac compressor Condenser fan Condenser Low line High line Accumulator Pressure sensor Other: O2 sensors Pcm Throttle body Plugs Wires Coilpacks Old: Everything behind the fire wall Line from compressor to condenser What the issue is: Can't get the ac clutch to self-engage even after truck reaches OT Current ambient temp: 63 F What I have tested: 10A fuse doesn't blow anymore 72472V relay is good Power to clutch plug connector is good 14.77v Reading at ac pressure sensor is 3.7 at continuity I can jump 30 to 87 to force the clutch to engage. When clutch is engaged by jumping 30 and 87 pins in relay and engine running AC on High coldest Low side pressure: 40 High side pressure: 135 AC off with clutch engaged Low side: 33 High side: turned AC on hi/coldest when pressure reached 300 and rising, pressure immediately dropped to 140 When clutch is not engaged and engine running AC on High coldest Low side pressure: 68ish High side pressure: 68ish AC off, no change When truck is not running Same pressures as when clutch is not engaged The truck will not engage the compressor to self regulate. Please help! Am I missing something?

[@christianmartinez7161]

Driver side vents blows warm at idle but cold when accelerating

[@vkarabin]

Can you tell me do you keep both gages in the open position or closed when testing.. thanks

[@ProfessorPentane]

The Manifold valves should be in the closed position The service valves on the end of the hose should be closed.

[@PANTYEATR1]

95 Mustang, my low side is maxed out on the gauge, the high side is at zero. Compressor clutch is disengaged. What's the problem? Thanks

[@vadimlazovskiy7442]

Thanks professor., just the scenario I am having now plus one more symptom - increase rpm slightly and pressure normalizes on both sides and cold air starts blowing. Basically I have no AC at idle or stand still traffick. I would not probably notice the issue but living in NYC, traffic is where average driver spends most of the time during summer. Is this additional detail points to the compressor or blockage?

[@Chris-kq7ko]

Increased rpm and your ac blows colder points to a weak compressor.

[@hasanasraf3717]

My high side reading is rattle? Is that normal?

[@yishihara55527]

My low side pressure goes all the way up to 150+ p.s.i. when the compressor cycles off and then down to around 50 p.s.i. after the clutch kicks in. It cycles every 5 to 10 seconds. System will blow cold air when driving but not at idle.

[@ProfessorPentane]

Low side pressure could be normal at 150 psi when off if the high side pressure is also 150 with the system equalizing. An orifice tube system will equalize very fast, around 30 to 45 seconds. PP

[@yishihara55527]

@@ProfessorPentane I ended up getting proper gauges. Low side when the compressor is ON is 50 p.s.i. but the high side is 375 to 400 p.s.i. When the car is off, both sides equalize to around 120 p.s.i. If the compressor was bad, I don't think the pressure on the high side would get that high. Seems like I have a blockage somewhere in the system, which is a nightmare because I might have to replace several components before I find where it is. It's incredibly hot here too, but garages want $1,500 to $2,000 o repair it when the car in only worth around $4,000 tops.

[@ProfessorPentane]

@@yishihara55527 Make sure the fan is coming on and there is good air flow through the condenser. A dollar bill should be able to stick to the front of the condenser when the fan is running. Poor airflow will cause your pressure to go high. Correct, the compressor is not bad. Which line is the high side service port is on, the liquid or discharge line?

[@ProfessorPentane]

You can also spray water at the condenser, if the pressure goes down, there is not a restriction.

[@yishihara55527]

@@ProfessorPentane High side service port is on the opposite side of the low side. Low side is the liquid side where I fill with refrigerant.

[@RMVZ58]

Good info, thanks man

[@peppi7777]

I have on the low side blue gauge 30 psi and on the high side red , gauge shows maxed out psi all the way high. Any suggestions why ,and thank you

[@Casualgaming763]

I think that means something is clogged

[@CoolArrow78233]

Can never find any info on Low side normal/high and High side normal. All the other conditions are easy

[@ProfessorPentane]

Air in the system because someone did not evacuate a previous repair would cause low side normal and high side high.

[@nathanw.1048]

​@@ProfessorPentane I had my 07 pt cruiser vacuumed out and tested for leak. It was recharged. High side reads normal. Low-key side goes over 60psi (up to 100) when AC clutch engages. Blows cold when driving, warm at idle. Will potentially stall engine when on at idle. We're thinking clogged condenser

[@kilezoe6603]

I let pressure out high side because I didn't have an understanding. So I need to pull vacuum on high side ?

[@ProfessorPentane]

Either side will work for pulling a vacuum before recharging the system. Thanks for watching. PP

[@douglasprovost768]

My car, a Renault, only has a low side connection. How should I diagnose problems without high side pressure information?

[@ProfessorPentane]

Hi Douglas, you can measure the temperature on the discharge line and then use a pressure/temperature chart on the internet to obtain the approximate pressure in the line. Good luck, PP.

[@KudirataduniSulaimon-dy1vf]

Hello please wanna learn how to repair and install car Ac

[@ILIKE2FIXSTUFF]

Mine is doing that. The compressor works but doesn't move the freon around on the system. Also, the radiator fan won't start when ac is turned on. Any tip on the radiator fan not turning on? I checked all fuses and relays

[@ChiefColeman]

My Cruze is doing the same thing. Fuses are all good too

[@ILIKE2FIXSTUFF]

Check the expansion valve if there is one there. If freon is good compressor kicks and too much pressure. Cold be the expansion valve.

[@yannickn6742]

Have you checked fan operation itself?

[@ChiefColeman]

@@yannickn6742 it was a bad compressor

[@bigwaves2824]

my low side is 80 psi and high side is 150 only 2 cans freon put in after changing the expansion valve high side gets real hot to touch low side is warm to touch any ideas the compressor turns and spins

[@Bobo-t5u]

I have the exact same problem 😂

[@bigwaves2824]

@@Bobo-t5u ended up being a bad compressor the suction side was bad swapped with a junkyard compressor works great know

[@Bobo-t5u]

@@bigwaves2824 thanks for letting me know. I'll do the same.

[@AlecFacemire]

@@Bobo-t5udid it work for you too? I have the same issue. Compressor holds with no leaks and kicks on properly but never gots cold I refilled it and emptied it 10 times and no change

[@Bobo-t5u]

@@AlecFacemire in my case, the system did end up blowing cool air, it drops the temperature by about 15 degrees but never gets very cold. During the summer, the ambient temperature in my area is in the 90s, so a 15 degree differential doesn't do much. If I'm on the highway (wind) and it's raining (water spraying on condenser) the system works fine. I think my problem is a bad/clogged condenser. I haven't had the time to replace it yet.

[@irisbaez1972]

I have a Kia soul 2012. 2.0L and the compressor are leaking a yellow liquid for some time. I've tried to seal it with RTV silicone, but I think is not working. Do you think I need to replace the compressor? This car has only 73 K miles, so why you think is leaking? We are in winter so we don't use it too much for now, but in summer this place will get 105 to 115 degrees. -- I have a quote to replace it for $ 1700.00

[@AlecFacemire]

You best just buy a pump from the junkyard and do it yourself and save 1600$ or maybe a brand new replacement compressor because KIA are just made very cheaply

[@ILIKE2FIXSTUFF]

I have a 2014 silverado and the ac compressor runs but doesn't seem to pump the freon around. Pressure on the low side is greater than high side which is odd. And... the cooling fans does not turn on when I turn the ac on inside the cabin. Fans work fine to cool the engine but not turning on for the ac. I unpluged the Pressure sensor and fans kick high speed. Any thoughts?

[@4.8_kris]

Did you ever figure it out ?

[@ILIKE2FIXSTUFF]

I replaced the expansion valve and went ahead and replaced the compressor that had a small leak. I really think the expansion valve was stuck or some. The fans will not engage with too low of pressure on high side. At least It is what I could think of. As soon as I replaced the expansion valve and compressor and refueled, it kicked in and works perfectly now.

[@selvinramirez5585]

Same problem I did exactly what you did with the pressure sensor, I’m go ahead and replaced the expansion valve first before I go with the compressor since the compressor it’s on and I really hope it’s not the compressor 😥$$$ I’ll come back next 2 weeks

[@rodrich870]

AC system Low side too low & High side normal . Can someone help me??

[@kasganjstudio1134]

Got any solution

[@issamadam9352]

If both are high 40-250 psi in a variable displacement compressor with IHX inspite of correct charge,what could be the cause?

[@victorbaca8010]

10:16

[@victorbaca8010]

Vb how do you check the orifice tube

[@victorbaca8010]

How do you check the orifice tube on a 1999 Ford F150

[@victorbaca8010]

How do you check an orifice tube on a 1999 Ford F150

[@victorbaca8010]

How do you check an orifice tube on a 1999 Ford F150

[@sharabi21]

Is the car running with the ac turned on ? Pl clear that before u het into specific details

[@ProfessorPentane]

Yes, the car is running with the A/C on.

[@oleboifishin5036]

I replaced compressor vacuumed everything and went to recharge and now i have a low reading but my high pressure side has no pressure

[@mikekorsak7771]

Blockage on the high side line, most likely orifice tube

[@ProfessorPentane]

It is odd that the high side as zero pressure, where is the high side service port? If it is the liquid line, there the condenser or receiver-drier is restricted. Recover again and make sure there is refrigerant in the system before replacing anything.

[@ProfessorPentane]

I agree Mike, thanks! PP

[@mikekorsak7771]

@@ProfessorPentane 🤘🏻

[@zeke4882]

D heck! You make everything complicated

[@jharrison6557]

Simplify it then for us

[@ronmelliad7327]

Awesome! Thanks!

[@bellybell542]

very educative video

[@mikefrayman5224]

Very dangerous job

[@GarageVegaUS]

I went to college for 13 months and now sometimes i fail, it's very hard sometimes but we learn something new everyday.

[@Brayco864]

Did he say 66c and 22% humidity ……. Does he not mean 22c and 66% humidity ?

[@wiley0714]

"It could be", professor? If you're going to diagnose some thing, then diagnose it. all this babble about what it "could " be ....

[@TanManFixes]

did you not read the heading? it said weak compressor lmfao

[@wiley0714]

It could be the TXV it could be the high ambient temperature from me making your blood boil enough to reply also.

[@natewilson111]

You seem to think he's trying to fix this one car with one problem. He's not. He's trying to give us ideas for what COULD happen to our own vehicles. Are you iD10t?