The A/C in my 1999 Coupe seems a bit on the wimpy side, so I was suspicious that the charge is low & I stuck a gauge on the low side.

I've got the A/C turned all the way up, compressor is running 100% of the time & the gauge reads about 60 PSI.

I'm confused. I expect a nominal charge to have it at 30-40 PSI.

Mike

 

At what eng speed are you seeing 60 PSI? Should be measured around 2k rpm. Increasing eng speed lowers the low side press and raises the high side press.

If we have 60 low and 350-400 high then it's safe to say it's overcharged. Without a high side reading it could be a correct charge and a weak comp.

What is the center duct temp? You might try playing with chg level and see how it effects the duct temp but we really need a high side press.

Look here:

http://forums.corvetteforum.com/show...ghlight=AC+101

 

I measured it at idle. I'll run it a gain tomorrow at 2K & check it against the chart. I can't measure the High-side, but I can measure Low & Center Duct Temp.

 

I'm not an HVAC person by any means, but if its running and just not as cold as it should be, have you cleaned out the rocks from the condensor?

 

Is it wimpy on outside fresh air only or on the inside recirculation ac button?

 

Okay, here is a better set of measurements.

Conditions; A/C set to manual, set 60 degrees, fan on High, Outside air. 2000 RPM, doors & windows open

Temp outside- 76 deg
Humidity- about 70%
Center Vent- 70 deg
Low-Side Pressure- 60 PSI & fluctuates +/- 5psi
Checked for diagnostic codes for A/C.... None
Checked for debris blocking the condenser... It's clear, & both fans run.

(If I set to Re-circulate, with doors & windows still open, it drops to 65 degrees)

A bit of history.... A/C worked fine the last 3 years. Nothing was serviced in that time (meaning nobody Overcharged it over the winter)

Note: I did the same test on my Pontiac sitting next to the Vette.... It makes 53 degree air.

 

Again, hard to say w/o a high side press. But from what you have posted here, I would say your compressor has gone "wimpy".

 

If your low side press didn't chg between idle and 2k rpm that points to a compressor that just can't get it any lower than that.

 

So, I'm inclined to get a proper set of gauges & a vacuum pump (only about $120 at Harbor Frieght), buy a compressor & swap it. It doesn't look that hard to get at. Am I missing anything?

Mike

 

Sounds like too much pressure to me. If my memory serves me, 25-45 psi is the normal range for a fully charged system. How is the compressor running? Cycling?...etc..

 

orfice or something is stopped up

 

The compressor runs continuously like it's suppose to. (As I understand it, this is not a cycling-type of system)

As to a plugged orifice... Isn't the low-side test port is down-stream of the orifice? If so, high pressure there is not consistent with an orifice plugged.

 

I agree with c5streak, high side pressure reading is important here.

 

Hi, I agree the high side pressures are needed, along with the ambient temps and humidity at the time of testing , the rpm's, and the center vent temp. It is possible with the 60psi low side reading to have any of the below mentioned problems
1, overcharge
2, bad compressor
3, extremely clogged condenser
4, improper chemical or air in the system
Let us know and we can help
Good Luck

 

Agree--Add #5--Orfice Tube split/broken, not enough restriction!

 

Gents,
Thanks... OK, Here is the collective possibilities list, my notes & a few questions:

1.) Overcharge- Nobody serviced this in at least the 3 years I've owned it & it used to work quite well... So, I think I can rule this out. (If this is still in question, I can always verify by bleeding some out.)

2.) Bad Compressor... (Does fit the symptoms, Its a candidate)

3.) Extremely Clogged Condenser.... If we're talking about the air passages; I got in there in looked. It's pretty clean. Just a small bit of debris at the top edge.

4.) Chemical or air in System. ( I think I can rule it out. It was working & nobody has been near it to put chemicals in. Pressure is way above ambient so air can't get in.)

5.) Orifice Tube damage, not enough restirction (does fits symptoms, it a candidate)

If I get a High-Side reading, can I tell the difference between a bad compressor & a bad orifice? If not, how do I seperate those 2?

I hate the thought of buying & replacing a compressor only to find it's the orifice. Do I do the opposite; change the orifice, evacuate, refill & test?

Thoughts?
Mike

 

My guess is bad compressor valves, but you need a high side reading to confirm. If nobody has touched the charge then you can rule out overcharge. If clean condenser you can rule that out but a high side reading will confirm. If no ones has touched it and it hasn't been empty of refrigerant then you can rule out non condensables. Oriface tube damage? I don't know what that means but in most cases the oriface or metering device can get plugged with moisture or debris if system was not properly evacuated but that will result in a lower pressure or compete restriction and a vacuum reading. I don't know much, but hvac I do know.

 

I've have not heard of an orifice tube malfunctioning and causing a reduced restriction, but it is feasible. That, or leaking valves in the compressor would both give you similar readings on your pressures. I think compressors go bad far more often then orifice tubes. A dirty condensor will give you very high readings on your high side.
That being said, here's what I would do:
1) Get accurate readings from both high and low side at the proper RPM.
2) Clean your condensor, it's free.
If that does not fix the problem, and the high pressure is below spec and low side is above spec,
3) Have the system evacuated and remove and inspect the orifice tube. If it is split or deformed bad enough to cause the problem, it will be obvious, and you can replace it.
4) If the tube looks good, then you need a new compressor. In which case you will need to evac the system and change the orifice tube anyway, along with the accumulator. You are out no extra expense by performing step #3.

 

Mike--

Lots of good advice here.

Here's a link that may be a big help:

http://trans5.com/docs/C5%20AC%20Com...eplacement.pdf

 

Hi, I agree, excellant logical way to proceed. FWIW, I've been doing HVAC work for 38 years and have worked on just about everything, cars, houses, commercial, industrial, military, and I've not yet seen an orifice break and cause a high pressure low side reading, but nothing is impossible. feel the liquid line on both sides of the orifice tube, if the temperatures are similar the orifice tube could be damaged. one side should be colder than the other. Also one other thing to look for, do the fans come on high speed when the ac is on, if not that could cause an overly hot condenser, and a high , low side reading and not much cooling. We really would know more with the other readings requested
Good Luck