GTM AC issue

[Keith1]

My GTM is a couple years out of completion and I have had some AC issues for which I'm worried my compressor is out. When the car was done I had the AC system charged. It worked great for the summer. It was stored over winter and the next spring the AC was out. The pressure readings were low. I put it under vacuum and it didn't leak. I wondered whether the Schrader valve for the low pressure line had a slow leak since when it was first charged the guy who charged it up questioned that. I put a new one in and recharged the system.

It worked great all last summer. It was stored during the winter again. When I took it out this spring the AC again was out. The pressures were low again but not zero. I tried to charge it again but now it looks like the compressor is out. The clutch engages and I can see it spinning but it doesn't put any strain on the engine at all when it engages. The high and low pressure ports both measure 50 psi and it doesn't change when the compressor engages. When I drive there is a definite difference in air temp coming out of the vents when the AC is on versus off so it seems that something is circulating but not enough to cause any pressure change, which makes me wonder how any cool air comes out at all.

Its a new LS3 with a new AC compressor. I put the required amount of PAG oil in the system. I even installed an RPM window switch to make sure I didn't have the compressor running over 4K RPMs. I have a couple of questions:

1. Is there anything else that could be acting this way other than a blown compressor?
2. If a blown compressor is the only thing that this could be how could it have happened, since it had oil in the system and it never runs past 4000 RPMs?
3. What is involved in replacing an AC compressor on a completed GTM? Does the body have to come off?
4. Does anyone want a GREAT deal on an essentially new GTM (1000 miles) with marginal AC?!

[Shoeless]

I learned something when I was very young from my dad, who was an auto mechanic his whole life. You need to cycle your AC on over the winter time to circulate the lube in the system and keep the seals in great shape or the system will leak.

I’d take it to an AC shop and ask them if they will put it under pressure and check it with their electronic leak detection unit. My dad had one and it would pick up on leaks you had no clue would exist. It would tell you exactly which seal to replace.

I’d start there before you go down the road of a compressor and it should be relatively cheap to check it.

[crash]

I'm not an AC guy, but I thought you needed to let the compressor "rest" once it was turned off so it didn't stall? AC Mikey is one of our resident HVAC guys. Might want to ping him either here or on the other site.

[Keith1]

When I had it under vacuum it stayed at -30 psi for over an hour. Wouldn't a leak show up with that?

[Keith1]

I'm ignorant with social media, how do you "ping" someone?

[Shoeless]

it may hold just fine for an hour, but could leak over time.

Crash is making reference to sending a private message to AC Mikey. Click notifications on the top and go to your inbox. From there on the left side is send new message. Click that and the put AC Mikey in the recipient box.

[Keith1]

Thanks Shoeless!

[beeman]

Make sure you install a new drier any time your system is opened up. Was your system open for any amount of time when you changed the Schrader valve? If you are holding pressure, I'd guess bad compressor vs moisture in the system.

Also, Vintage Air has great tech support. You usually have to leave a voice mail with your name and phone number, but they usually call back in 15-30 minutes...

[VRaptor SpeedWorks, LLC]

There is only one possibility I can think of that would cause the conditions you're talking about. If there is a definite difference in air temp out the vents with compressor on vs off, but the pressure doesn't change between high and low side.....the only thing I can think of that might cause this is that your orifice tube blew out of place. So you still have refrigerant circulating thru the system....but you don't have the pressure drop thru the orifice that's required to lower the temp of the refrigerant in the evaporator core. Unfortunately, on a finished car, that might actually be way worse than having the compressor go out.....since the extension tube that the orifice installs into is all but impossible to remove from the AC unit without tearing things apart in the tunnel.

[Keith1]

Shane,
Do you know of a way to determine if that's the case? It seems odd that the system worked fine up to when I stored the car in a heated garage for the winter and then it wasn't working correctly the first time I took it out in the spring. I have no idea what would cause an orifice tube to become dislodged, but it seems unusual to me that this would happen when it was just sitting.
Keith

[Keith1]

Make sure you install a new drier any time your system is opened up. Was your system open for any amount of time when you changed the Schrader valve? If you are holding pressure, I'd guess bad compressor vs moisture in the system.

Also, Vintage Air has great tech support. You usually have to leave a voice mail with your name and phone number, but they usually call back in 15-30 minutes...

It wasn't open for long at all when the valve was changed, just swapped them out. I put the system under vacuum for a long time to remove moisture before recharging. Thanks for the suggestion to call Vintage Air, it couldn't hurt.

[VRaptor SpeedWorks, LLC]

The only way I can think of to verify this is to start the engine, kick the AC on, open up the hood and feel the temp of the high pressure alum AC line going into the top of the condenser and compare that to the temp of the suction alum AC line connected to the accumulator that goes back to the compressor. If there is a definite temp difference in those 2 lines, your compressor has to be circulating refrigerant. If there was a pressure difference, I would probably just get another orifice tube, drain the refrigerant, take apart the hose connection at the end of the extension tube where the orifice goes, install a new orifice, put it back together, vac and charge it and see if that fixes your problem. I guess if the old orifice got pushed into the evaporator core and it's just rattling around as a loose part in there, it probably won't hurt anything?

[Keith1]

Thanks Shane.

I just got off the phone with Vintage Air. They said they don't use orifice tubes, thats an FFR request that VA builds for them, he said in their systems they use expansion valves. He didn't have any experience with orifice tubes and couldn't comment on them. He thought it sounded like the compressor was bad but couldn't explain the air temp difference with AC on.

I don't have the heater bypass valve installed in my system, I rely on the AC to adjust cabin temp. I wonder if the temp change in the cabin that I feel is just due to outside air rather than the AC system working at all. I thought that since the heater core is always hot when the car is at operating temp the only thing that can cool it at all is the AC, since the outdoor air is already flowing through the core. Am I mistaken? When the heat is on is the outside air flow restricted in VA systems to just recirculate cabin air? The VA tech help guy wasn't sure.

[acmikee]

PM sent im in the process of moving to Utah from washington
are you sure that the compressor is cycling on. if you think that is leaking at the low side service port put some soap bubbles on it or if you dont have any have any just spit on it. the pressure should change when it is on. if the low side drops to a vac it is a bad or plugged orifice what is the standing pressure when off

[VRaptor SpeedWorks, LLC]

Thanks Shane.

I just got off the phone with Vintage Air. They said they don't use orifice tubes, thats an FFR request that VA builds for them, he said in their systems they use expansion valves. He didn't have any experience with orifice tubes and couldn't comment on them. He thought it sounded like the compressor was bad but couldn't explain the air temp difference with AC on.

I don't have the heater bypass valve installed in my system, I rely on the AC to adjust cabin temp. I wonder if the temp change in the cabin that I feel is just due to outside air rather than the AC system working at all. I thought that since the heater core is always hot when the car is at operating temp the only thing that can cool it at all is the AC, since the outdoor air is already flowing through the core. Am I mistaken? When the heat is on is the outside air flow restricted in VA systems to just recirculate cabin air? The VA tech help guy wasn't sure.

The VA unit has no way to recirculate air. Yes, the heater core will always be hot if you don't have the coolant shut-off installed. With the AC on and the temp knob at full cold, 100% of the air should come in thru the blower motor, thru the evaporator and out to the vents. If you turn the heat knob to partial heat, all that does is route part of the airflow thru the heater core after it has already gone thru the evaporator. Tough to imagine VA having an employee answering people's questions who doesn't know how a system with an orifice tube works?

[Keith1]

The VA unit has no way to recirculate air. Yes, the heater core will always be hot if you don't have the coolant shut-off installed. With the AC on and the temp knob at full cold, 100% of the air should come in thru the blower motor, thru the evaporator and out to the vents. If you turn the heat knob to partial heat, all that does is route part of the airflow thru the heater core after it has already gone thru the evaporator. Tough to imagine VA having an employee answering people's questions who doesn't know how a system with an orifice tube works?

Maybe the cool air I'm feeling with AC on is just outside air routed around the heater core.

ACMikee was kind enough to talk to me today. After trying a few things that didn't work he thinks that its likely the compressor. He said that if it was the orifice tube there should be at least a small difference in pressure from high to low ports. Some fun awaits me. Has anyone changed one on a GTM with an LS3? Can it be done without engine removal?

[VRaptor SpeedWorks, LLC]

Yes...while it looks like a real PITA.....and it sort of is.....it's not the worst thing I've ever done to replace the compressor on a finished car. If you have the Kooks headers, you'll have to remove the pass side header. Remove the belly pan below the front of the engine and you'll have to do most of the work from under the car. The whole thing is pretty straight forward with the worst part being that a couple of the compressor bolts can't be removed from the compressor until you get the compressor out....which means you have to remember which bolts those are and put them thru the new compressor before you put the new one in position....and the whole time you're trying to get the old one out and the new one in, those bolts are sliding around getting caught on everything and on the way in, trying to fall out....and all 4 bolts are different, so you have to remember which ones go where.

[Keith1]

Yes...while it looks like a real PITA.....and it sort of is.....it's not the worst thing I've ever done to replace the compressor on a finished car. If you have the Kooks headers, you'll have to remove the pass side header. Remove the belly pan below the front of the engine and you'll have to do most of the work from under the car. The whole thing is pretty straight forward with the worst part being that a couple of the compressor bolts can't be removed from the compressor until you get the compressor out....which means you have to remember which bolts those are and put them thru the new compressor before you put the new one in position....and the whole time you're trying to get the old one out and the new one in, those bolts are sliding around getting caught on everything and on the way in, trying to fall out....and all 4 bolts are different, so you have to remember which ones go where.

Thanks Shane!

I put the car on jacks today and took the plate off under the front of the engine. There is fluorescent green dye on the plate and around the hoses in this area. There isn't any dye on or around the compressor. There is currently 50 psi pressure in the system which has held steady since trying to recharge it. I ran the car with AC on and tried to find any leaks in the lines but couldn't find any. This is a real head scratcher. If there's a leak big enough to spew dye why does it hold pressure and vacuum? If the compressor blew and the leak is from the compressor why is there no dye around the compressor? If its just a malfunctioning compressor why is there leaked dye?

I have an appt for next tuesday with an AC shop to have someone take a look at this and see what they think.

[HardRocker]

There is fluorescent green dye on the plate and around the hoses in this area. There isn't any dye on or around the compressor.

I would bet front compressor seal is leaking under pressure but not vacuum.

[Keith1]

I would bet front compressor seal is leaking under pressure but not vacuum.

It seems like there would be green dye around the compressor area but there isn't any. I wonder if there was a leak around the Schrader valve in the tunnel which leaked while I had the car stored for the winter and when I ran it this spring the compressor was running for a short while and maybe there wasn't enough oil in the system after the leak and compressor blew. I didn't run it much at all, it does seem strange to me that it would go out with that minimal amount of use, and there had to be at least a bit of oil in it even after the refrigerant leaked out. I don't know, not my wheelhouse so I'm grasping at straws here.

[VRaptor SpeedWorks, LLC]

About all I can recommend there is to thoroughly clean off the AC hoses in that area and let it sit a few more days and then use a blacklight to see if you can spot where the leak is. Could be coming from where the hoses crimp to the aluminum or part of the T weldment where the schrader valve is. Yeah, if there is no dye around the compressor, you should be able to rule that out.

Also, you should be able to tell if your AC compressor is OK or not (for the most part) by just turning the compressor by hand. If it seems to turn smoothly and has some resistance to spinning it (much like turning an engine by hand)....and is not rough or locked up, the compressor is probably ok.

[Keith1]

About all I can recommend there is to thoroughly clean off the AC hoses in that area and let it sit a few more days and then use a blacklight to see if you can spot where the leak is. Could be coming from where the hoses crimp to the aluminum or part of the T weldment where the schrader valve is. Yeah, if there is no dye around the compressor, you should be able to rule that out.

Also, you should be able to tell if your AC compressor is OK or not (for the most part) by just turning the compressor by hand. If it seems to turn smoothly and has some resistance to spinning it (much like turning an engine by hand)....and is not rough or locked up, the compressor is probably ok.

Thanks Shane, good ideas.

Does anyone know why there is a Schrader valve in that location? It seems like a needless potential leaking spot that serves no purpose.

I have the AC appt tomorrow at a shop. I will let you know what they think.

[VRaptor SpeedWorks, LLC]

The schrader valve is for the C5 pressure sensor. If you were using a C5 ECU, you wire up the system so that it is controlled by the ECU. The blue wire that normally energizes the compressor clutch....on the C5 ECU, you would wire that into the "AC request" input of the ECU and then the ECU turns the AC compressor on and off and the pressure sensor is wired to the ECU in the same way it was on the 'Vette. On the LS3, there is no way to use the ECU to control the AC since GM moved that function to the BCM instead of the ECU....sort of.

[Keith1]

The schrader valve is for the C5 pressure sensor. If you were using a C5 ECU, you wire up the system so that it is controlled by the ECU. The blue wire that normally energizes the compressor clutch....on the C5 ECU, you would wire that into the "AC request" input of the ECU and then the ECU turns the AC compressor on and off and the pressure sensor is wired to the ECU in the same way it was on the 'Vette. On the LS3, there is no way to use the ECU to control the AC since GM moved that function to the BCM instead of the ECU....sort of.

Thanks Shane, that makes sense.

[Keith1]

I took the car to a mechanic today. He cleaned off all the lines at the back of the car. He wasn't entirely sure whether it was coolant or AC dye/oil. We did notice a tiny drip coming from the thermostat housing hose and we wondered if all the green stuff was actually coolant. We tightened that clamp a bit more. He vacuumed the AC lines and recharged it. It took pretty much a full AC charge, he said there was about 3 oz in the system. Why it wouldn't take a charge from my system is a mystery, maybe his had more pressure. The system filled and the AC works now. He thought maybe the compressor wasn't generating a pressure differential due to a lot of air in the lines. We ran the car and looked for any leaks and the only thing we could find was a tiny drop under one of the fittings to the dryer. I'm going to drive it for the summer and see how this goes. If I continue to see drips under the dryer line hose I will change the O ring. So, long story short, it doesn't look like there is any major problem, just a slow leak that may just be an O ring. Thanks for everyone's input, especially Shane!

[Shoeless]

Glad to hear it wasn’t something major like changing the compressor.