How much oil came out of your old AC compressor?

[Sjohns4]

When you replaced your AC compressor (I think HT6 is the type - the one with 4 vertical bolts), how much oil drained out of the old one? I bought a new 4440 Sanden Compressor for my 97 Suburban. My old compressor was leaking, it didn’t detonate. Followed the directions and drained oil out of the old compressor to match the volume in the new one. There was very little oil that came out of the old compressor. What came out was clean and light colored, although heavier than what the factory sanden had in it.

What worries me about matching oil level in the new compressor to the old was there was an obvious leak in the old compressor. The sanden Service Guide gives suggestions for additional oil for leaks, but I’m thinking if a fair amount of oil settles in the compressor, and the compressor is off, I’ve lost a fair amount of liquid oil rather than what would normally be mixed with refrigerant when it’s seeping out a seal in the system somewhere?

Additionally, when I bough the truck the system wasn’t holding pressure. I put the compressor on from the donor engine, put some amount of oil in it, pulled vac, charged, and it worked good for the past 5 years. I feel I had it close enough then, and I feel comfortable there’s not junk in my system, I’m just not comfortable I’m going to get the right amount of oil in the compressor this time around.

With all the hose and fittings for the rear air I think a complete flush and refill is impractical.

My thought is my overall system is probably saturated with oil, it’s in all the places it would normally settle, and it didn’t leak from any of these places, so the only question is how much needs to be in the compressor itself (plus the additional 2-3 oz for new accumulator)? I also reason since I’m focused on just the oil in the compressor itself, pickup vs. suburban wouldn’t matter too much?

Just looking for a sanity check to see what’s typically in the compressors.
Open to critiques on my logic too.

Thanks,

Mike

 

[GoToGuy]

Just follow the FSM recommendations for replacement and recharge according to parts replaced. It's about the minimum oil for operation.

 

[ChrsLytn]

When you replaced your AC compressor (I think HT6 is the type - the one with 4 vertical bolts), how much oil drained out of the old one? I bought a new 4440 Sanden Compressor for my 97 Suburban. My old compressor was leaking, it didn’t detonate. Followed the directions and drained oil out of the old compressor to match the volume in the new one. There was very little oil that came out of the old compressor. What came out was clean and light colored, although heavier than what the factory sanden had in it.

What worries me about matching oil level in the new compressor to the old was there was an obvious leak in the old compressor. The sanden Service Guide gives suggestions for additional oil for leaks, but I’m thinking if a fair amount of oil settles in the compressor, and the compressor is off, I’ve lost a fair amount of liquid oil rather than what would normally be mixed with refrigerant when it’s seeping out a seal in the system somewhere?

Additionally, when I bough the truck the system wasn’t holding pressure. I put the compressor on from the donor engine, put some amount of oil in it, pulled vac, charged, and it worked good for the past 5 years. I feel I had it close enough then, and I feel comfortable there’s not junk in my system, I’m just not comfortable I’m going to get the right amount of oil in the compressor this time around.

With all the hose and fittings for the rear air I think a complete flush and refill is impractical.

My thought is my overall system is probably saturated with oil, it’s in all the places it would normally settle, and it didn’t leak from any of these places, so the only question is how much needs to be in the compressor itself (plus the additional 2-3 oz for new accumulator)? I also reason since I’m focused on just the oil in the compressor itself, pickup vs. suburban wouldn’t matter too much?

Just looking for a sanity check to see what’s typically in the compressors.
Open to critiques on my logic too.

Thanks,

Mike

I've had the same gray area questions every time I replaced a compressor. I've drained the old compressor, turned pulley some to get all of it in there out and it wouldn't be much at all. I don't remember now exactly how much I decided to put in it. It's been a couple of years. But it's working fine now while I'm slowly typing this out.

 

[1998_K1500_Sub]

You've got a Suburban and I assume it's got rear air.

Recommended oil is 11oz (by volume), and 4# R134a (64oz by weight). The same mass of R134a, in liquid form, occupies 50.8oz (by volume).

Back-of-the-napkin, let's assume, in operation, that all of the R134a is in liquid form in the high-side of the system, along with much of the oil. That's 63oz total (liquid, about 1/2 gallon). Obviously it'll be less b/c some will be in the low-side, but...

There's a lot of room in that system for oil and compressed (liquid) refrigerant on account of the larger (Suburban) condenser and length of high-pressure lines (front and rear).

If you feel uneasy about "too little" oil based on the amount you've removed, you aren't going to go too wrong by adding an additional 1oz to the system, e.g., via the compressor. Having 12oz in the system instead of 11oz changes the total volume of liquid in the system by only 1.6%.

If in doubt, you can always perform the test described in the Sanden "SD Compressor Service Guide", Section 6.8.3, pg. 11, to check whether the system oil charge is adequate to keep the compressor lubricated. This test isn't easy, but it would be telling.

What's interesting is Sanden's guide, Section 6.8.1, says "The Sanden SD series compressor achieves optimal durability and cooling performance when oil circulates through the system at a ratio of 3.3% to 8% oil to refrigerant."

Does Sanden mean "%tage by volume"? If so, then the Suburban's %tage is around 18%, using my numbers from above. Then again, maybe not all the oil is circulating in the Suburban, so the "%tage circulating" would be lower. I'll have to look into this; perhaps their spec is "%tage by weight".

With all the hose and fittings for the rear air I think a complete flush and refill is impractical.

Agreed. In particular, the rear lines, where they meet the TXV and rear evaporator, can be impossible to separate after years of exposure to the elements. Ask me how I know. It's a rip-and-replace process.

 

[JDGMC]

You've got a Suburban and I assume it's got rear air.

Recommended oil is 11oz (by volume), and 4# R134a (64oz by weight). The same mass of R134a, in liquid form, occupies 50.8oz (by volume).

Back-of-the-napkin, let's assume, in operation, that all of the R134a is in liquid form in the high-side of the system, along with much of the oil. That's 63oz total (liquid, about 1/2 gallon). Obviously it'll be less b/c some will be in the low-side, but...

There's a lot of room in that system for oil and compressed (liquid) refrigerant on account of the larger (Suburban) condenser and length of high-pressure lines (front and rear).

If you feel uneasy about "too little" oil based on the amount you've removed, you aren't going to go too wrong by adding an additional 1oz to the system, e.g., via the compressor. Having 12oz in the system instead of 11oz changes the total volume of liquid in the system by only 1.6%.

If in doubt, you can always perform the test described in the Sanden "SD Compressor Service Guide", Section 6.8.3, pg. 11, to check whether the system oil charge is adequate to keep the compressor lubricated. This test isn't easy, but it would be telling.

What's interesting is Sanden's guide, Section 6.8.1, says "The Sanden SD series compressor achieves optimal durability and cooling performance when oil circulates through the system at a ratio of 3.3% to 8% oil to refrigerant."

Does Sanden mean "%tage by volume"? If so, then the Suburban's %tage is around 18%, using my numbers from above. Then again, maybe not all the oil is circulating in the Suburban, so the "%tage circulating" would be lower. I'll have to look into this; perhaps their spec is "%tage by weight".



Agreed. In particular, the rear lines, where they meet the TXV and rear evaporator, can be impossible to separate after years of exposure to the elements. Ask me how I know. It's a rip-and-replace process.

3.3 - 8% by weight.

 

[GoToGuy]

The R134 is sold by weight. As when servicing in shops many weigh the container before and after servicing charging $$ for the refrigerant by ounce weight.
You can do the physics in whatever form. The point is refrigerat in pressurized is weighted product. Converting to liquid, volumetric measurement is great science , yet not in service procedure.

 

[1998_K1500_Sub]

3.3 - 8% by weight.

What is your reference?

Did Sanden say (and I missed it)?



(edit) I get it now.

The density of PAG is ~1gm/cm.

So 1oz (by volume) of PAG weighs about 1oz (by weight).

So the "%tage by weight" of oil/refrigerant is easy to determine.

On the Suburban it's 11oz oil, 64oz R134a.

%tage of oil to refrigerant is ~17%

 

[JDGMC]

What is your reference?

Did Sanden say (and I missed it)?



(edit) I get it now.

The density of PAG is ~1gm/cm.

So 1oz (by volume) of PAG weighs about 1oz (by weight).

So the "%tage by weight" of oil/refrigerant is easy to determine.

On the Suburban it's 11oz oil, 64oz R134a.

%tage of oil to refrigerant is ~17%

Perfect! I didn’t have a reference, but when describing a thermodynamic variable with a vapor-liquid equilibrium or liquid-liquid under pressure you would use mole% (mass). You may already know all this, but I’ll continue just in case. To characterize the behavior you factor in velocity and pressure. The relationship is important to model the startup and shutdown or cycling of the compressor. Keeping the viscosity of oil just right to move through the system fast enough to keep those bearings happy. Unfortunately when the compressor shuts off and cools down much of the oil drops out and pools at the lowest point. All the hose bends and the component locations create much of the wear and tear on the compressor at startup. Kinda like putting your oil pan at the rear of the vehicle - cold starts would be harsh.

 

[1998_K1500_Sub]

Unfortunately when the compressor shuts off and cools down much of the oil drops out and pools at the lowest point.

I often think about this ^^^

My Suburban (like others) has a LONG run of HP and LP line to the rear, and both run beneath the floor of the body... "down low".

I wonder how much PAG pools in the LP line; I wonder how often the gas velocity in the LP line gets high enough to drag the oil all the way up to the wye in the LP circuit to the compressor.

Whenever I run the AC I make a point to have the rear blower fan on, at least to LOW and generally higher, simply to generate flow in that refrigerant circuit.

I'll often turn down the front HVAC fan to LOW and cool the vehicle with the rear AC, to the extent possible.