WTF Last Question About AC

[GoldenEagleFan]

The saga continues.... Went to a service station this morning in my small village, nice mechanics and very friendly. Ask if they can hook up the low and high side gages on my AC so I can see what is going on. It was 78F 55% humidity. Low side was 70 PSI, High side was 110PSI. Suggested it was low on freon so they
did an evac and only 14 oz. comes out. Vacuumed the system, recharged with 3.4 lbs of R134 and go to check the gages. Running at idle the high side was 190-200PSI, low side went into the retard range which incicates 350 PSI????. However, the air was blowing at 58F at high fan speed and the system now works great. I watched the entire operation so I don't suspect any funny business, but how can the low side pressure be higher than the high side? What is going on here? Am I in danger of ruining the system? The guys seemed knowledgable about AC and said it shouldn't be a problem but that doesn't sound right...Any thoughts?

[Alexlind123]

The saga continues.... Went to a service station this morning in my small village, nice mechanics and very friendly. Ask if they can hook up the low and high side gages on my AC so I can see what is going on. It was 78F 55% humidity. Low side was 70 PSI, High side was 110PSI. Suggested it was low on freon so they
did an evac and only 14 oz. comes out. Vacuumed the system, recharged with 3.4 lbs of R134 and go to check the gages. Running at idle the high side was 190-200PSI, low side went into the retard range which incicates 350 PSI????. However, the air was blowing at 58F at high fan speed and the system now works great. I watched the entire operation so I don't suspect any funny business, but how can the low side pressure be higher than the high side? What is going on here? Am I in danger of ruining the system? The guys seemed knowledgable about AC and said it shouldn't be a problem but that doesn't sound right...Any thoughts?

Didnt you ask them why the low side was higher?

[GoldenEagleFan]

I think I was trying their patience on a SAturday morning as a walk in, I got there must be a problem with the evaporator, or there are metel shavings causing a problem (I don't beleive so as I checked the oil out of my old compressor and no shavings) so bring it in, will tear it down, give it a flush and go from there.

I am trying to figure out how I can have low side pressure 1.5X the high side and still have great cooling. Doesn't make sense. At this point I guess I'll run it and see what happens.

[GoldenEagleFan]

The high side gage is right before the expansion valve and reads 200PSI. Fluid goes into the evaporator, cools down and comes out a higher pressure??? Not possible me thinks...

I guess the gage being in the retard range is telling me your're a retard for thinking you can fix the A/C system yourself.

[Bill R.]

low side, you're in a vacum. LOOK at the gauge and you'll see where zero is, you're needle is below zero not turned all the way around to 350. Any point below that zero on the gauge is inches of vacum. Which means that the expansion valve is stuck shut and the compressor is sucking really really hard trying to pull gas through that expansion valve,which makes it go down into a vacum. Go check the pressures again. I'm pretty sure you're going to end up replacing the expansion valve.




The high side gage is right before the expansion valve and reads 200PSI. Fluid goes into the evaporator, cools down and comes out a higher pressure??? Not possible me thinks...

I guess the gage being in the retard range is telling me your're a retard for thinking you can fix the A/C system yourself.

[Bill R.]

low system charge, it indicates that either the expansion valve is wide open and not providing any restriction or you have some damaged valves on the compressor and its not pumping correctly.



The saga continues.... Went to a service station this morning in my small village, nice mechanics and very friendly. Ask if they can hook up the low and high side gages on my AC so I can see what is going on. It was 78F 55% humidity. Low side was 70 PSI, High side was 110PSI. Suggested it was low on freon so they
did an evac and only 14 oz. comes out. Vacuumed the system, recharged with 3.4 lbs of R134 and go to check the gages. Running at idle the high side was 190-200PSI, low side went into the retard range which incicates 350 PSI????. However, the air was blowing at 58F at high fan speed and the system now works great. I watched the entire operation so I don't suspect any funny business, but how can the low side pressure be higher than the high side? What is going on here? Am I in danger of ruining the system? The guys seemed knowledgable about AC and said it shouldn't be a problem but that doesn't sound right...Any thoughts?

[GoldenEagleFan]

I watched the gage as the mechanoc started the car and it definitely went from about 10PSI pressure, rotated to the right and continued climbing until it went past 200PSI into the "retard" range.

When they evacuted only 14 oz. of freon came out so I did believe them when they say it was undercharged. (I stood by the machine and watched the whole time).

The suction line runs nice and ice cold, the pressure line is slightly warm into the evaporator and the line from the compressor to the condenser is very warm.

I can;t complain about the performance of the system now, it blows nice and cold, but an just freaked out about the pressure on the low side.

I going tomorrow to buy a set of gages so I can check things out myself.

[Bellicose Right Winger]

Sounds like a defective low side gage.

Paul Shovestul



I watched the gage as the mechanoc started the car and it definitely went from about 10PSI pressure, rotated to the right and continued climbing until it went past 200PSI into the "retard" range.

When they evacuted only 14 oz. of freon came out so I did believe them when they say it was undercharged. (I stood by the machine and watched the whole time).

The suction line runs nice and ice cold, the pressure line is slightly warm into the evaporator and the line from the compressor to the condenser is very warm.

I can;t complain about the performance of the system now, it blows nice and cold, but an just freaked out about the pressure on the low side.

I going tomorrow to buy a set of gages so I can check things out myself.

[joshua43214]

I think I was trying their patience on a SAturday morning as a walk in, I got there must be a problem with the evaporator, or there are metel shavings causing a problem (I don't beleive so as I checked the oil out of my old compressor and no shavings) so bring it in, will tear it down, give it a flush and go from there.

I am trying to figure out how I can have low side pressure 1.5X the high side and still have great cooling. Doesn't make sense. At this point I guess I'll run it and see what happens.

Ya, I am sure their patience at near zero. AC is complex stuff and takes many years of experience to know allthe ins and outs of it. They are not going to share any of their experience with you for the piddling cost of an evac and recharge so you can go home and do it yourself.

I will on occasion share experience with people that want to do their own repairs, but on certain things, especialy AC and drivability, I clam up real fast.

So, here is your diagnosis, though several people have already stated it, you need an expansion valve.

[GoldenEagleFan]

I feel like I'm on the quest for the Holy Grail... I know the A/c system has no real impact on the performance of the auto. This has become my search...I went into this knowing nothing about A/C, and now know more than I ever care to. It's now become personal and emotions are overiding logic.

These damn E34's. "I can't quit you"

[Bill R.]

get an accurate number before coming to any conclusions.



I feel like I'm on the quest for the Holy Grail... I know the A/c system has no real impact on the performance of the auto. This has become my search...I went into this knowing nothing about A/C, and now know more than I ever care to. It's now become personal and emotions are overiding logic.

These damn E34's. "I can't quit you"

[GoldenEagleFan]

Just realized tonight talking to my son's friend that here in Wisconsin I cannot buy a gage set to check my pressures. One of only two states (California is the other) that will not allow self service of A/C. Good thing I'm heading to our cabin in upper Minnesota next week...

[Bellicose Right Winger]

Gages are nice, but there are other less expensive performance indicators. Ice cold, sweating return line as you've noted is a good one. A thermometer in the dash vent will tell you most of what you need to know. Should run at 38-42F. Somewhat higher in traffic. On the highway you should see it cycle as controller prevents evaporator freezeup.

http://members.cox.net/wdixon27/325%20radio.JPG

I feel a whole lot better knowing I'm the ONLY one driving around with a thermo in the dash vent!

Paul Shovestul



Just realized tonight talking to my son's friend that here in Wisconsin I cannot buy a gage set to check my pressures. One of only two states (California is the other) that will not allow self service of A/C. Good thing I'm heading to our cabin in upper Minnesota next week...