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A/C line pressures

Weezul

Full Member
Joined
Feb 24, 2015
Messages
60
It's in the 90s here in Memphis during the hot part of the day.  I have the AC in my 2005 Avalanche set on 60 with the fan speed on high and it blows air out around 64 degrees.  On my wife's CRV with the AC set at 60, it blows around 50 degrees.  The interior of the Avalanche stays comfortable at best but will not freeze me out of it.  I've got an appointment scheduled for Tuesday to have it looked at.  I borrowed a low pressure gauge from a friend (he didn't have a high pressure gauge for me to check that) but the low pressure went to around 100 psi.  From what I've read, it should be around 35 psi.  I hooked it up to the CRV and it was right around 37 psi.

Does this mean that the system is overcharged?  What should proper high and low pressures be in the lines?  I just want to know what to look for when I have it checked so that I know what to be expecting from the mechanic.
 
Interested in your outcome. Same issue on my 05. It keeps me comfortable but will not freeze me when it's 90 out
 
Need high pressure to know.

Might be under filled and/or not enough air across condensor or Evap as all of these things effect pressure in Refridgerant as does ambient temps.

My guess is you areslightly low and have a small leak somewhere since it is a sealed system.
 
Loaned the gauges from AutoZone and checked the pressures.  Ambient temp is 85 degrees.  Low pressure is 62 psi and high pressure is 200 psi. 
 
Sounds like you are low on Refridgerant...

See when compressor cycles off the tend to equalize...
then it kicks in and the low pressure drops and high increases...

I forget values but I think in the 30-40psi range... again depends on temp.

BEst thing for you to do is go to AC mechanic and have him hook up gages.
If low ASK where is leak because it could happen again...

 
If it is low wouldn't the low side psi be lower than 30-40 psi and not up at 62 psi?
 
Weezul said:
If it is low wouldn't the low side psi be lower than 30-40 psi and not up at 62 psi?
NO.
Remember when you start truck the pressure is Equal from High to low.

Then when it starts compressing on the high side and sucking on the low side....
The high pressure goes thru expansion valve and this is where you measure low pressure.
If not enough refridge the pressure drop is not much so not very low...

All tjhis from some dayum Thermodynamics engineering course many many many Moons ago.. heck more then moons SEASONS ago.
 
Gotcha. I hate engineering. Haha. Talked to a friend and he said to check it at 1,500 or so rpm and the low side should be around 40 psi. Gonna do that tonight and see what it reads.

I rolled the front windows down and put the fan at half speed at the request of a friend and ran it for 10 minutes and the vent temp read 50 degrees. At full fan speed, it reads around 60-62. Is that normal?
 
Look a the low pressure switch on the accumulator/drier. See if it looks like there oil or it's dirty around it. It's common for those to go out and  leak, the diaphragm blows out in them just from wear and tear since they cycle about a billion times..

The good news if that is the problem you just replace that and top off the charge. The switch is about $50.00 at the dealer, cheaper at the auto parts store/on-line. There is a Schrader valve and O-Ring under it so you don't open the system to atmosphere, you can just R&R with a wrench in about a minute. Just do not over tighten, just a little more that hand tight, it seals with the O-Ring not the threads.

Then just top it off or have shop do it and your good to go.. Good luck





 
Low pressure switch is spotless. At 1500 rpm low is at 45 and high is at 225. Temp is still blowing at 60 from the vents on high speed. If I turn the fan down 2 speeds, vent temps drop to 40.
 
HTH

R-134a Pressure Temperature Relationship

Pressures shown in the charts are provided as a general guide and may not represent your exact readings. Ambient temperature is measured 2 inches in front of the condenser.

Low Side Readings     Evaporator Temperature     High Side Readings     Ambient Temperature
     (PSI)                         (Fahrenheit)                        (PSI)                        (Fahrenheit)
    16-29                              33-50                          115-200                          70-80
    19-39                              33-60                          140-235                          80-90
    25-43                              40-65                          165-270                         90-100
    37-51                              48-65                          210-310                        100-110
 
Weezul said:
Low pressure switch is spotless. At 1500 rpm low is at 45 and high is at 225. Temp is still blowing at 60 from the vents on high speed. If I turn the fan down 2 speeds, vent temps drop to 40.



Actually these reading don't look to bad.. Does your 05 have electric fans. If not then your not moving to much air through the condenser  when parked so it's not removing all of the heat from the refrigerant. Take the temp reads moving down the road above 30 mph and the temps may come down..

If you do have electric fans make sure the condenser and radiator are clear of debris.. 
 
I have electric fans. I'm installing a trans cooler tomorrow so I'll make sure the radiator and condenser are clean. I saw the 40 degree vent temp when I was driving home from work today.
 
So I found out my AC was BADLY leaking out of the high pressure port and the O-ring for the low pressure switch was in bad shape when I pulled off the low pressure switch.

I bought a "rebuild" kit for the shraeder valves and replaced the inserts for the low pressure switch and low pressure side, replaced the o-ring for the low pressure switch and while trying to figure out the high pressure port found it was leaking bad enough to release any vacuum built up in under 10 seconds. After replacing these and the high pressure port I looked up how much these trucks need and it said 1.6 lbs which comes out to 25.5 oz. It also stated 1.5 Oz of oil.  I used a couple of 12oz cans hoping it would be enough since my system was totally empty. (Could only pull 20 units of vacuum on the system with the venturi pump I used..)
Those cans each had 1oz of oil in them and additives that were supposed to neutralize any acids due to moisture in the system.

After filling my system I was reading 50/200 using the high side from my gauge manifold and low side from the filler tube. (used a dedicated fill adapter with inline fuse since I couldn't figure out how to do it properly with the manifold without additional fittings.)
While hooking the low side of my manifold back up I didn't realize at first the valve was open so I vented a little coolant back out.

End pressures after this opps was about 40/195 psi.  Was 75-80F outside at the time and the truck was idling.

That was about a week and half ago. I am considering pulling pressures on it again before leaving for nationals but may just bring my gauges and fill tube with me in case it is still leaking. Even debating grabbing a couple spare cans in case can't find any in the area. Been told it is very hot down there right now. Thing I resolved my issue but can't be 100% sure.


So anyhow, from what I am seeing my pressures seem reasonable? And my truck was COLD yesterday when I turned it on and went for a short drive.

Rodney
 
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