Question about a/c pressure readings

I get 29 on the low side, 115 on the high running at idle. The refrigerant line is cold under the hood, compressor comes on! So could it just be my blend door? Compressor maybe....would think my high side would be higher? It was about 77 degrees. Any thoughts? I know you guys know your cars here so know you can help. Thanks.

I get 29 on the low side, 115 on the high running at idle. The refrigerant line is cold under the hood, compressor comes on! So could it just be my blend door? Compressor maybe....would think my high side would be higher? It was about 77 degrees. Any thoughts? I know you guys know your cars here so know you can help. Thanks.
the low side with r134 is normally around 40-50psi ...@1200 rpm

75-85 deg f ..high side should be 280 psi I've seen 330 psi depends on how hot out and condition of the system...charge...

115psi on high side I would check your gauges ..cannnot not be that low..lowest is around 225psi ...

The gauges I bought are Yellow Jacket professional gauges they are a week old and I paid good money these. Maybe I am reading my gauges wrong.... this is a gauge that reads 12/22/134a... on the 134a scale I get 115 on the high side...but then theres a scale thats on the outermost of the gauges and doesnt specify refrigerant, just says psi... that shows about 148psi. Hope that helps to clarify?





the low side with r134 is normally around 40-50psi ...@1200 rpm

75-85 deg f ..high side should be 280 psi I've seen 330 psi depends on how hot out and condition of the system...charge...

115psi on high side I would check your gauges ..cannnot not be that low..lowest is around 225psi ...

The gauges I bought are Yellow Jacket professional gauges they are a week old and I paid good money these. Maybe I am reading my gauges wrong.... this is a gauge that reads 12/22/134a... on the 134a scale I get 115 on the high side...but then theres a scale thats on the outermost of the gauges and doesnt specify refrigerant, just says psi... that shows about 148psi. Hope that helps to clarify?


these guages are a manifold charging set..? the valves on the ends should be closed..if open pressure can flow from high side to low reducing pressure..

like I said 115 psi is not correct ...

these guages are a manifold charging set..? the valves on the ends should be closed..if open pressure can flow from high side to low reducing pressure..

like I said 115 psi is not correct ...

Yes they are a charging set, and the valves were closed. So my readings being what they are, what does that mean? Restricted?

Yes they are a charging set, and the valves were closed. So my readings being what they are, what does that mean? Restricted?


use the pressure readings on the outer edge of guage..I would say you are a little low on refrigerent with the 148psi on the high side...

when you add refrigerent you will see a rapid rise in pressure when you begin to approach the maximum amount of refrigerent that is the systems capacity...I would look to get that pressure to around 200psi..see how it runs @80deg F air temp...

it is best to start with the system empty then install the correct amount. this way you know that it is charged correctly . then with the engine at 1200 rpm record the pressures hi/low and the air temp..

then at another time , when you check your system you will have a good indication of the systems charge or proper operation...

also measure the temp of the air blowing out the interior vents..

only connect/disconnect the high side guage with the ac OFF...after pressure has droped..

Yes they are a charging set, and the valves were closed. So my readings being what they are, what does that mean? Restricted?
As said high side is low.
We need the gauge readings at idle and at 2K with engine warm and compressor running.
Gauge reading should change with compressor running and compressor cycling off when low side drops below cutoff pressure.
Post back all pressure readings low and high side.

Here are pics of my gauges! I get 115 on blue 134a scale at idle, second row in...... what does the outer psi scale show/mean? I wont be at the car till Sunday to see what I get at 2,000 rpm.
I pulled a vacuum 525microns for 45 minutes and then filled....I add 12 ozs of refrigerant and then stopped since there was no change in air temp. I put a dig a/c thermometer in the vents and got 77 degrees.

use the pressure readings on the outer edge of guage..I would say you are a little low on refrigerent with the 148psi on the high side...

when you add refrigerent you will see a rapid rise in pressure when you begin to approach the maximum amount of refrigerent that is the systems capacity...I would look to get that pressure to around 200psi..see how it runs @80deg F air temp...

it is best to start with the system empty then install the correct amount. this way you know that it is charged correctly . then with the engine at 1200 rpm record the pressures hi/low and the air temp..

then at another time , when you check your system you will have a good indication of the systems charge or proper operation...

also measure the temp of the air blowing out the interior vents..

only connect/disconnect the high side guage with the ac OFF...after pressure has droped..

Here are pics of my gauges! I get 115 on blue 134a scale at idle, second row in...... what does the outer psi scale show/mean? I wont be at the car till Sunday to see what I get at 2,000 rpm.
I pulled a vacuum 525microns for 45 minutes and then filled....I add 12 ozs of refrigerant and then stopped since there was no change in air temp. I put a dig a/c thermometer in the vents and got 77 degrees.


the pressure is the outer red area, this would be about 150psi ..disrgard the inner guage refrigerent marks...

you installed 12 oz. of r134 you need more refrgerent should be around 32 oz.or a little more ,,, make sure you only install what your capacity is NO MORE !

as you install the refrigerent monitor the high side pressure ...then you will notice the air temp drop when the pressure rises...it is the change in pressure from high to low that causes the cooling of air [the absorbstion of heat from air ].....with low pressures on high side you can not get cool air ...

the pressure is the outer red area, this would be about 150psi ..disrgard the inner guage refrigerent marks...

you installed 12 oz. of r134 you need more refrgerent should be around 32 oz.or a little more ,,, make sure you only install what your capacity is NO MORE !

as you install the refrigerent monitor the high side pressure ...then you will notice the air temp drop when the pressure rises...it is the change in pressure from high to low that causes the cooling of air [the absorbstion of heat from air ].....with low pressures on high side you can not get cool air ...


Ok, thanks, I will add the rest of refrigerant and hope for cold air! The system says it takes 2.0lbs. I just was confused when my low side lines were cold/sweating but inside the car it wasnt cold at all, so I didnt go further and add anymore refrigerant.
My initial problem was that the compressor was cycling on and off but I wasnt low on refrigerant. But the system had been opened for other work, for over 2 weeks and then just refilled with no vacuum so that may have created excessive air or system causing the compressor to cycle on and off. I will finish the fill up Sunday and see how it goes! Thanks again.

you vacuumed the system and the vacuum held at 500microns this is good...now with the air removed you should get , with the proper refrigerent install a very good cooling ....

what you saw on those lines getting very cold, but no cold air coming out is because the evaporator was only cold on the supply end ....not the complete evaporator coil length ...many times with a low charge ice can build up there , but little cooling of the air ..this was very common with the R12 refrigerent which did work much better ...too bad it eats up the atmosphere , R12 works much better..


post back with how it all works ..

you vacuumed the system and the vacuum held at 500microns this is good...now with the air removed you should get , with the proper refrigerent install a very good cooling ....

what you saw on those lines getting very cold, but no cold air coming out is because the evaporator was only cold on the supply end ....not the complete evaporator coil length ...many times with a low charge ice can build up there , but little cooling of the air ..this was very common with the R12 refrigerent which did work much better ...too bad it eats up the atmosphere , R12 works much better..


post back with how it all works ..


Hey was just curious....I just picked up a 30lb sealed cylinder of R134a for $150 cash.....is that a deal?

Hey was just curious....I just picked up a 30lb sealed cylinder of R134a for $150 cash.....is that a deal?
A good deal for the seller.:rofl:
And always make sure it is the good pure stuff.
And be sure to have a good set of scales to weigh what you are putting in.

I get a lot of 30 lb. kegs for 79.95 US $ sometimes 89.95$

A good deal for the seller.:rofl:
And always make sure it is the good pure stuff.
And be sure to have a good set of scales to weigh what you are putting in.

I get a lot of 30 lb. kegs for 79.95 US $ sometimes 89.95$

Wow! Where do you get them for that price? Maybe because I'm in NY it's expensive?

Carquest and O'rielly and Auto zone.
Always watch for specials on it.

Yes NY may have a higher market.

Carquest and O'rielly and Auto zone.
Always watch for specials on it.

Yes NY may have a higher market.

Just called my local carquest, $219 a tank! Refrigeration supply house near me wants $240!

Just called my local carquest, $219 a tank! Refrigeration supply house near me wants $240!

Sounds like you are in a high price NYprice district.

Sounds like you are in a high price NYprice district.

Yeah so I guess 150 was a deal out near me! If I'm ever out your way I will be sure to stock up!

Well back to rule no always check price before pricing.

I just called O'reilly and Carquest.

O'reilly was 170 30 lb keg and Carquest was 179 30 lb keg.

Whow I just bought some this spring for 79$ keg.

Looks like AC recharging is going way up in price.

Good Luck

Well back to rule no always check price before pricing.

I just called O'reilly and Carquest.

O'reilly was 170 30 lb keg and Carquest was 179 30 lb keg.

Whow I just bought some this spring for 79$ keg.

Looks like AC recharging is going way up in price.

Good Luck

Then I guess the price I paid was a deal! Too bad you didn't buy more kegs, could have resold and doubled your money. How much should a keg of R22 run? Household use.
Btw I called Sams club, they have 30 134a for $150! Not sure which brand though.

Then I guess the price I paid was a deal! Too bad you didn't buy more kegs, could have resold and doubled your money. How much should a keg of R22 run? Household use.
Btw I called Sams club, they have 30 134a for $150! Not sure which brand though.

Not sure on the R-22.
I forgot about sams club.
I used to buy some from them before I could get better deal at local parts place.

Several years back when everybody went to R-134 it shot way up and then dropped down.

Looks like a person better stock up when the price is down.
Good Luck

Not sure on the R-22.
I forgot about sams club.
I used to buy some from them before I could get better deal at local parts place.

Several years back when everybody went to R-134 it shot way up and then dropped down.

Looks like a person better stock up when the price is down.
Good Luck


Does anyone have a pressure temperature scale/chart? How do I know what the correct low/high side pressure range is?

Does anyone have a pressure temperature scale/chart? How do I know what the correct low/high side pressure range is?

finding a chart specificly for this/your vehicle may be difficult to get..

just install the correct charge and report the results ..

Old school is every lb of pressure = one degree tempture.

28-32 low side pressure gives you 28-32 degrees cooling in evaporator.
With lose of 5 or more degrees before it shoots out vents.

Below 26-28 degrees low side compressor low side switch shuts of compressor to keep evaporator from freezing up.

150 -250 high side is good pressures.

High side depends a lot on condensor air flow cooling.

Sitting inside shop I always put a fan on condensor to help air flow and hold down pressure.

As J-cat says tell us you pressure readings at idle and at 2k with compressor running engine warm but not real hot with correct charge and air flow threw condensor and also vent tempt readings.

finding a chart specificly for this/your vehicle may be difficult to get..

just install the correct charge and report the results ..

Was taking a look at a friends silverado 1500 5.3v8 2003....it was 92 degrees today... but my truck thermometer showed 102...I got 48 low side and 247 on the high side at idle. I didnt have anyone around to get readings at 2000rpm. The coldest the vents got was about 59. Is that normal on a extremely hot day like today is?

Was taking a look at a friends silverado 1500 5.3v8 2003....it was 92 degrees today... but my truck thermometer showed 102...I got 48 low side and 247 on the high side at idle. I didnt have anyone around to get readings at 2000rpm. The coldest the vents got was about 59. Is that normal on a extremely hot day like today is?

with the temps today 90 plus having 48 psi low and 250 high with the air venttemp around 59 deg is very good ...having a drop of 35 deg from the 93 deg f air temp is what you what to see..

see how the high side pressures change with temp and charge .
also with vehicle design , condition of the cooling fan etc....

always best to be slightly under charged than over charged ...

Was taking a look at a friends silverado 1500 5.3v8 2003....it was 92 degrees today... but my truck thermometer showed 102...I got 48 low side and 247 on the high side at idle. I didnt have anyone around to get readings at 2000rpm. The coldest the vents got was about 59. Is that normal on a extremely hot day like today is?


also on the R134 refrigerent that now we must use and this coil design with this refrigerent. when the DEWPOINT TEMPS rise above 60 degrees these r134 ac units cannot handle the condensating water generated..as a result this reduces the ability to cool the air...

when r12 was in use the coil design did not have this negetive effect on the cooling ...coil fin spacing is much larger with these ...

Was taking a look at a friends silverado 1500 5.3v8 2003....it was 92 degrees today... but my truck thermometer showed 102...I got 48 low side and 247 on the high side at idle. I didnt have anyone around to get readings at 2000rpm. The coldest the vents got was about 59. Is that normal on a extremely hot day like today is?

You need to get all of the readings.
Not just as quick one time snap shot.
Watch the change from idle to 2K rpm and the pressure changes on low side.
What is the on and off pressure reading on low side?

You need to get all of the readings.
Not just as quick one time snap shot.
Watch the change from idle to 2K rpm and the pressure changes on low side.
What is the on and off pressure reading on low side?


Ok I am here at the car that we were talking about during the week. I refilled the system to the proper amt, per weight. The air inside is still warm :( I get 42 on the low side and 160 on the high at idle. At 2000 rpm I get about 42 on the low and it goes up to 195 on the high. The coldest I get it on the vents inside is 64 degrees. When I gas it to 2000 rpm I can get it down to about 62 degrees. I am in a cool garage. Thoughts please...I am here only today to work on this vehicle. If you want 845-242-7985. It sounds like the compressor is engaged when I hit the a/c button and then shut it off it shuts off. I do think I hear it click on and off initially...but cant guarantee that. Thanks.

Ok I am here at the car that we were talking about during the week. I refilled the system to the proper amt, per weight. The air inside is still warm :( I get 42 on the low side and 160 on the high at idle. At 2000 rpm I get about 42 on the low and it goes up to 195 on the high. The coldest I get it on the vents inside is 64 degrees. When I gas it to 2000 rpm I can get it down to about 62 degrees. I am in a cool garage. Thoughts please...I am here only today to work on this vehicle. If you want 845-242-7985. It sounds like the compressor is engaged when I hit the a/c button and then shut it off it shuts off. I do think I hear it click on and off initially...but cant guarantee that. Thanks.

With compressor running and engin at 2 K rpm the low side should should swing down to around 28 and the compressor shutoof and kickbac inand lowside should start droping back down.
You have a problem if low sideis holding steady 42.
If the low side is holding 42 your gauges are not connecting or bypassing or expansion orfice is bad.

Ok I am here at the car that we were talking about during the week. I refilled the system to the proper amt, per weight. The air inside is still warm :( I get 42 on the low side and 160 on the high at idle. At 2000 rpm I get about 42 on the low and it goes up to 195 on the high. The coldest I get it on the vents inside is 64 degrees. When I gas it to 2000 rpm I can get it down to about 62 degrees. I am in a cool garage. Thoughts please...I am here only today to work on this vehicle. If you want 845-242-7985. It sounds like the compressor is engaged when I hit the a/c button and then shut it off it shuts off. I do think I hear it click on and off initially...but cant guarantee that. Thanks.

since this is charged correctly and its around 80-85deg out I would say the evaporator is dirty / or the air filter in the air box needs replacing...high side pressures should be higher than 160-190 psi ..if the evaporator can't get the proper air flow it will run like this ..

then it also could be internal restrictions ..

since this is charged correctly and its around 80-85deg out I would say the evaporator is dirty / or the air filter in the air box needs replacing...high side pressures should be higher than 160-190 psi ..if the evaporator can't get the proper air flow it will run like this ..

then it also could be internal restrictions ..


Ok since I only have one day a week to work on this vehicle I had do something. So I decided to recover the refrigerant and then check orifice tube. I pulled and it had debris on it...small black rubber like particles. I didnt have a new one so i just cleaned it out with carb cleaner and then reinstalled, vacuumed and refilled. I got better readings this time, though not perfect. I now get 48 on the low side and 190 on the high at idle. At 2,000 rpm I get still about 48 on the low but the high side 226. The coldest I got the vent temperature was 44.5 degrees while driving with the air flowing through the condensor. At idle I get about 54 degrees.
So my conclusion is that my compressor is on its way out? I was glad though I bought a little time, maybe the rest of this season to keep me cool.
Do you guys still think replacing the cabin filter may help out?

Ok since I only have one day a week to work on this vehicle I had do something. So I decided to recover the refrigerant and then check orifice tube. I pulled and it had debris on it...small black rubber like particles. I didnt have a new one so i just cleaned it out with carb cleaner and then reinstalled, vacuumed and refilled. I got better readings this time, though not perfect. I now get 48 on the low side and 190 on the high at idle. At 2,000 rpm I get still about 48 on the low but the high side 226. The coldest I got the vent temperature was 44.5 degrees while driving with the air flowing through the condensor. At idle I get about 54 degrees.
So my conclusion is that my compressor is on its way out? I was glad though I bought a little time, maybe the rest of this season to keep me cool.
Do you guys still think replacing the cabin filter may help out?



I like those pressure readings . the vent air temp is good.
the restriction in the ocifice caused the refrigerent to not flow ...

the cabin filter still should be checked every year . this will get the high side pressures higher as the system will absorb more heat , and a faster cool down of cab..

Ok since I only have one day a week to work on this vehicle I had do something. So I decided to recover the refrigerant and then check orifice tube. I pulled and it had debris on it...small black rubber like particles. I didnt have a new one so i just cleaned it out with carb cleaner and then reinstalled, vacuumed and refilled. I got better readings this time, though not perfect. I now get 48 on the low side and 190 on the high at idle. At 2,000 rpm I get still about 48 on the low but the high side 226. The coldest I got the vent temperature was 44.5 degrees while driving with the air flowing through the condensor. At idle I get about 54 degrees.
So my conclusion is that my compressor is on its way out? I was glad though I bought a little time, maybe the rest of this season to keep me cool.
Do you guys still think replacing the cabin filter may help out?



carb cleaner should not be used . this product is for metal only. rubber and plastics get damaged ....

using mineral spirits paint thinner , or throttle body / maf cleaner then blow dry ...

this orifice being restricted may have damaged the compressor ..at this time it appears to be working...the rubber may be just a dirty system , or the rubber is breaking down. did you add a few oz of PAG 150 refrigerent oil ? with the amount of work done it would be good to add some oil..

carb cleaner should not be used . this product is for metal only. rubber and plastics get damaged ....

using mineral spirits paint thinner , or throttle body / maf cleaner then blow dry ...

this orifice being restricted may have damaged the compressor ..at this time it appears to be working...the rubber may be just a dirty system , or the rubber is breaking down. did you add a few oz of PAG 150 refrigerent oil ? with the amount of work done it would be good to add some oil..

Yeah I added 3oz of oil recharge. pag 150. I hope the compressor keeps working and no damage was done!