A/C shuts off 2 or 3 times & then stays on.

[froggy47]

I have the FSM & can go thru most of that, but I am thinking low 134 pressure.

It blows pretty cold when on but recently I have had to hit the a/c button several times to get it to stay on.

Just looking for prelim info, what to look for before I start.

Thanks.

If I top it off to correct pressure & use one of those cans with a "sealant" is there a specific brand you recommend.

I may put some dye in and have a look with the infared light.

BTW NO HVAC codes.

:)

[Junkman]

I would NEVER "top off" a R-134a system without knowing EXACTLY how much refrigerant is in there beforehand. R-134a systems are NOT like your old freon systems. The amount of R-134a that is in your system is critical to its proper operation. What you need to do is have a evacuation & recovery done so that you will know exactly how much refrigerant to add. They will also add the dye necessary to detect any leaks, and do a leak down test to boot.

You do NOT want to just go pumping unknown amounts of refrigerant into your system. The specs are very specific and can vary across the years.

[froggy47]

Originally Posted by Junkman

I would NEVER "top off" a R-134a system without knowing EXACTLY how much refrigerant is in there beforehand. R-134a systems are NOT like your old freon systems. The amount of R-134a that is in your system is critical to its proper operation. What you need to do is have a evacuation & recovery done so that you will know exactly how much refrigerant to add. They will also add the dye necessary to detect any leaks, and do a leak down test to boot.

You do NOT want to just go pumping unknown amounts of refrigerant into your system. The specs are very specific and can vary across the years.

Thanks Junkman.

I know you mean well.


I have a pressure manifold & can top off to an exact pressure but I do not have the professional equipment to do it by evacuation & weight.

So (in So Cal anyway) I am looking at DIY & a few minutes of my time for about $25.

vs

take it to some over regulated over priced HVAC shop or dealer who won't even look at it unless I sign an authorization for about $500. and who will (at the end of the day) probably want to replace the compressor & all the other chit for over $1500.

That, unfortunately, is the about where it stands. The shops that do HVAC have a sort of "monopoly" on a/c leaks due to the EPA, CARB, etc etc regulations and when a business has a monopoly, well, at least I'd like dinner & a movie before I get.....

[ToolGuy]

I do occasional AC work just with the cans and AC gauges from the local auto stroes. Not the best, but for the seldom times I do it, it works OK.

If you see the 134 chart for your current outside temp and humidity below, figure out the low pressure side should be per the temp and humidity numbers and then connect your gauge to the low side for a reading.

This is what I do and if I need to add then I do. I also use any can at the store that has the trigger, so I can control the flow better and not waste the entire can after a top off. The kinds that just have a tap are not that easy to control.

In this post is the 134 chart I am speaking of for pressures on the low side. High side too if your gauges have a high and low side gauge.

http://corvettemechanic.com/forum/51...ion-c4-c5.html (ac problem guestion for c4/c5)

I check all my cars to the chart and you can even put in a tiny bit more for even better cooling, but do not over charge! A tiny bit more to me, is rounding up on the reading for the low side.

Beyond this, I can't recommend that the issue might be myself. But checking the pressure to the chart is a start.

[froggy47]

Here are some numbers on my a/c

2004 z06

Engine off
55psi low
45psi high

Engine on a/c on
25psi low
160-230 psi high

Outlet temps 38-40 deg f

A/c comp does NOT cycle at idle speed always on

------------------------------------------------------------------------

2000 Suburban 5.3

Engine off
75psi low
80psi high

Engine on a/c on
45 psi low
200-225 psi high

Outlets 50-55 deg f

a/c comp does NOT cycle at idle rpms

-------------------------------------------------

Added 8oz 134 to vette 4psi increase on low side
Added 4oz 134 to Sub maybe 1.5 psi increase on low side

_______________________________________

Did not freeze anything off or blind myself in spite of scary warnings on equipment & 134.

--------------------------------------------------

Any thoughts comments welcome

I do not believe either a/c system was ever serviced b4 today.

The chart provided by ToolGuy was for 98 vette at 1000 rpm so I do not want to draw any rash conclusion, BUT it seems to me the vette "could be" low (even after the service) on both low and high side.

Ambient was 75f and humidity was 70%

Do any of you tech guys have the Sys Performance Test specs for 2004 Vette?

Thanks in advance.

_____________________________________-

[Junkman]

Originally Posted by froggy47

...take it to some over regulated over priced HVAC shop or dealer who won't even look at it unless I sign an authorization for about $500. and who will (at the end of the day) probably want to replace the compressor & all the other chit for over $1500.

Wow. A mom and pop shop only charged me $50.

The bad thing about it is my buddy checked the system with those gauges you all are talking about and everything showed correct. He's a ASE Master Technician of untold years so I know he knows what he's doing. However, the evac and recovery machine showed that I only had .4 pounds of R-134a instead of 1.5 pounds, which is what my car is supposed to have.

Because of that experience, I'll always spend the $50 and get some data that I can work with.

[ToolGuy]

Here's the 2004 GM serv info. Its written a little different then the one above ironically.

[ToolGuy]

Here's a 2000 for comparison as well. I should have stated earlier the charts are pretty much the same, some are just easier to read then others. At least now you got the 04 and can print it off and keep it in your files.

And yes I would agree, the 04 seems a low by the charts. I really feel myself a top off should stop it from going on and off. I don't see anything in the manuals to check for this condition either.

It odd because I've worked on three cars that AC was not real cold, topped them off and all worked great. In each case, the cars were older, thus I guess the charge just gets weaker as the car ages and no leaks are found. The one car was cooler on the pass side than the drivers side. GM serv said to top off and check outlet temps. I did that and it was back to ice cold. I checked my 98 Vette and it's still where it needs to be and is ice cold, but I'm waiting for one summer to top it off since I've never done it myself.

[ToolGuy]

Here's the GM infor for when the compressor won't engage. I know this is not your issue, but its the closest in the manual.

You can read down, but it does state to check pressures and go to leak checks at one check point. I dont suspect a leak for you, but my point is it states check perssures first which you are doing! : )

Oh and the 2000 Surb has more Lbs refrigerant because back then, vehicels had more and cooled better. Now, some cars are lucky to have a Lb and dont cool well at all!

[LLC5]

Originally Posted by froggy47

Here are some numbers on my a/c

2004 z06

Engine off
55psi low
45psi high

Engine on a/c on
25psi low
160-230 psi high

Outlet temps 38-40 deg f

A/c comp does NOT cycle at idle speed always on

------------------------------------------------------------------------

2000 Suburban 5.3

Engine off
75psi low
80psi high

Engine on a/c on
45 psi low
200-225 psi high

Outlets 50-55 deg f

a/c comp does NOT cycle at idle rpms

-------------------------------------------------

Added 8oz 134 to vette 4psi increase on low side
Added 4oz 134 to Sub maybe 1.5 psi increase on low side

_______________________________________

Did not freeze anything off or blind myself in spite of scary warnings on equipment & 134.

--------------------------------------------------

Any thoughts comments welcome

I do not believe either a/c system was ever serviced b4 today.

The chart provided by ToolGuy was for 98 vette at 1000 rpm so I do not want to draw any rash conclusion, BUT it seems to me the vette "could be" low (even after the service) on both low and high side.

Ambient was 75f and humidity was 70%

Do any of you tech guys have the Sys Performance Test specs for 2004 Vette?

Thanks in advance.

_____________________________________-

What were your ambient temps and humidity when these were taken, and what engine speed? For max a/c cooling you will want about 2000-2500 rpm's and high pressures could be as high as 350# with high humidity and ambient temps. A general rule of thumb is that if the outlet duct temps are within 25-30F of ambient temps (lower of course), with the windows rolled up blower on high and in the recirculate mode position, then the vehicle is cooling good. Good luck with it.