A/C Guys - question about low/high pressures

[IHaveAMustang]

I have a 2007 Corolla that has A/C that is..."meh".

It's super finger biting cold in the morning, but as soon as it hits around 95* or sits in the sun a while, the air blows cool, but not cold.

I hooked up my manifold gauges and saw low and high side were low (25/200) so I added a can of straight R134 and now have the following pressues:



The R134 chart said it should be 40-55 Low side and 275-300 high side, but that isn't fully universal.

Driving around yesterday evening ambient was about 90 but the sun had gone down and it seemed to blow cooler. Are pressures correct?

Also, this cars previous owner had the Compressor/Condensor replaced at Pep Boys and they put a TON of UV dye in it. Should I evac, purge, pull a vacuum and then add R134 to make sure the dye isn't causing issues? They didn't even replace the drier from what I can tell.

When system is off/car is off, pressures do equalize and so I am thinking/hoping it is not an expansion valve or blockage in the lines. That requires 8 hours of labor to remove the entire dash and replace HVAC box.

[DON SVO]

If they used the pag oil/dye combo you could have too much oil in the system.

[IHaveAMustang]

If they used the pag oil/dye combo you could have too much oil in the system.

And that would diminish cooling ability? I'm still learning all of this.

[IHaveAMustang]

Also, considering they didn't replace the drier or silica packet in the drier - I wonder if I have moisture or air in the system. I found this chart online of pressures and associated problems - any truth to them?

https://www.buyautoparts.com/blog/what-are-my-ac-pressure-readings-telling-me-about-my-ac-system/

An A/C System that is working properly should have 150 PSI on the high side and 30 PSI on the low side.

Obviously the main issue that people deal with when they have a broken A/C system is that the air coming out the vents is not cold enough. Here is a list of the pressure readings that are characteristic of an A/C compressor that is not blowing cold air into the cabin of your car:

250 PSI / 30 PSI = You have air somewhere in the system.

250 PSI / 50 PSI = The system is overcharged and the condenser is not cooling. Condenser may be blocked.

225 PSI / 80 PSI = It is likely that the expansion valve is opened too wide (not the case if your A/C system has an orifice tube) Also, you could have too much refrigerant in the system.

200 PSI / 70 PSI = There is a blockage somewhere in your system either before or at the expansion device.

160 PSI / 10 PSI = It is possible that the evaporator is frosted, the low pressure piping is faulty, or the expansion valve might be clogged. Check the evaporator, piping, and expansion valve to locate the source of the issue.

150 PSI / 30 PSI = There is water in the system.

150 PSI / >10 PSI = Your expansion valve might be stuck open, or there could be a leak somewhere you in your system.

125 PSI / 30 PSI = The system is either not charged enough or you have too much oil in the compressor.

100 PSI /100 PSI = The compressor is not engaging because there is no power coming to it or you have a burnt coil.

50 PSI / 50 PSI = The clutch is not engaging.

For more information on Interpreting AC Pressure Readings, check out our How To page on the subject, CLICK HERE.

[juiceweezl]

I'm not knowledgeable beyond hooking a can up from Vato Zone to add a little refrigerant, but isn't there supposed to be a pressure adjustment due to temperature? The can I used had a gauge that you rotated the "green zone" to based on the temperature. I know you alluded to ambient temperature, but I do not know if you adjusted pressure because of it.

[JC316]

Also, considering they didn't replace the drier or silica packet in the drier - I wonder if I have moisture or air in the system. I found this chart online of pressures and associated problems - any truth to them?

https://www.buyautoparts.com/blog/wh...-my-ac-system/

Whoever wrote that chart is a fucking idiot. I've never seen a properly working A/C system with 150/30 pressure and a blockage produces well over 200PSI on the high side.

Your pressure looks fine, but what was the ambient and engine temp? I've seen them get like that on a hot day, but throwing some water on the condenser will drop it way down. Another question is if that car has a cabin air filter? Could be clogged and limiting your a/c performance.

I'm not knowledgeable beyond hooking a can up from Vato Zone to add a little refrigerant, but isn't there supposed to be a pressure adjustment due to temperature? The can I used had a gauge that you rotated the "green zone" to based on the temperature. I know you alluded to ambient temperature, but I do not know if you adjusted pressure because of it.

Absolutely. Hotter it is outside, the higher the pressures will read.

[shumpertdavid]

I do all my repairs with an A\c Recovery machine. The pressures don't look bad but it's too difficult to determine charge amount strictly based on pressures alone. If I had to base charge level just on the pressures alone, I'd say you have a little room to add a small amount more. By that, I mean .25 lb or so. I'd strongly recommend having someone with a recovery machine evacuate the system and verify the charge amount accordingly. The systems capacity on small and newer cars are too low to charge by cans accurately.

[IHaveAMustang]

Whoever wrote that chart is a fucking idiot. I've never seen a properly working A/C system with 150/30 pressure and a blockage produces well over 200PSI on the high side.

Your pressure looks fine, but what was the ambient and engine temp? I've seen them get like that on a hot day, but throwing some water on the condenser will drop it way down. Another question is if that car has a cabin air filter? Could be clogged and limiting your a/c performance.

Engine was operating range (just below middle)

Ambient was 95 but I was in my garage.

Cabin filter was just replaced - I thought that might be the issue, and it helped airflow but not temp.

I do all my repairs with an A\c Recovery machine. The pressures don't look bad but it's too difficult to determine charge amount strictly based on pressures alone. If I had to base charge level just on the pressures alone, I'd say you have a little room to add a small amount more. By that, I mean .25 lb or so. I'd strongly recommend having someone with a recovery machine evacuate the system and verify the charge amount accordingly. The systems capacity on small and newer cars are too low to charge by cans accurately.

Going to the Pep Boys tomorrow where the compressor and condenser were installed and the evac/charge was completed. At the very least they can verify that.

Thanks for the advice and input. A/C never has been an easy "DIY" item, without investing a lot in equipment.

[BP]

Too much oil can cause a restriction somewhere in the system. Make sure your recirculation or max button is turned on and that all the air is blowing from the dash vents. If one of the blend doors is open it'll definitely affect cooling.

[JC316]

Engine was operating range (just below middle)

Ambient was 95 but I was in my garage.

Cabin filter was just replaced - I thought that might be the issue, and it helped airflow but not temp.





Going to the Pep Boys tomorrow where the compressor and condenser were installed and the evac/charge was completed. At the very least they can verify that.

Thanks for the advice and input. A/C never has been an easy "DIY" item, without investing a lot in equipment.

Being that hot, it might be giving you higher pressures. You can splash some water on the condenser and see how far it drops. Might just need a little more freon. Odds are pretty good that pepboys half assed the job and it either has too much oil, air, or moisture in the system.

Probably going to need to be evacuated, flushed, new drier, new orifice tube, properly vacuumed, and refilled with the proper amount of oil and freon.

[JPM]

Does it have two fans on the rad? Maybe the one that comes on auto with the a/c isn't working?

[IHaveAMustang]

Does it have two fans on the rad? Maybe the one that comes on auto with the a/c isn't working?

Single fan - whopping 1.8L engine. Runs when system comes on.


But there has been resolution in this matter. I took the car into the Pep Boys that replaced the condensor/compressor back in April (2,000 miles ago) before it was salvaged out.

They said there was entirely too much dye in there and so they evac'd the entire system and recharged it with R134 with no dye. I don't think the dye was the problem, but instead some other contaminants.

45* at the vents now. Nice and cold. They didn't make me pay anything, which hints at they may have messed up originally, or not...

Either way, problem solved.

Thanks for all the info, this was a learning experience for me.

[BP]

A lot of "mechanics" don't think it's necessary to pull a vacuum on an a/c system before charging, maybe you had one of those? Shops like Pep Boys usually have a reclaimation/charging station that does everything for you but that doesn't mean the tech used it.

[IHaveAMustang]

A lot of "mechanics" don't think it's necessary to pull a vacuum on an a/c system before charging, maybe you had one of those? Shops like Pep Boys usually have a reclaimation/charging station that does everything for you but that doesn't mean the tech used it.

I'd honestly never take my car to Pep Boys for A/C work. I'd go to an actual shop that specializes in A/C repairs/diagnosis. But this car was owned, no joke, by a little old lady and she probably got swindled into it during her oil change.

Oh well, new compressor/condenser and A/C charge on her dime is nice.

[blackedv]

She didnt get swindled into it as the compressor was leaking and the drier is attached to the condensor so it was changed. What im wondering is how there is dye everywhere under the hood of it? We use a pag oil that has dye in it so we can see any leaks in the system in the future but someone did something to that system as just the dye alone under the hood probably accounts for a few oz of oil. I dont know if the writer told you but there is dye absolutely everywhere which threw me for a loop. I always dump the old compressor oil out and put the same amount back into the new compressor so when it left a few months ago the oil charge was correct as it could be. All ac systems I do get a good vacuum period. Im wondering if there is a leak in the system and they just did a quickfill with a can before selling it instead of bringing it back to us to see what might be leaking. You said you put a can in it but it was only slightly overcharged so theres probably a leak somewhere but you need to degrease the underhood to have a chance to find it. I was the one that did the initial work and looked at it yesterday.I do specialize in ac repair and diagnostics and can tell you that car did not leave with the ac barely working a few months ago.