AC

N

nm8shun

Member
Hello!

AC has never blown cold as I’ve owned the car. Decided I need to fix it. Here are the details;
1. Fan blows in the cabin. But it’s not cold.
2. The compressor runs and the clutch engages (I can see it in the engine bay).
3. AC manifold gauges show 100 psi (low and high) in 90ish degree weather before car is turned on.
4. When car is on and AC is activated (fan on, snowflake button active), the Low Side drops to 80ish and the high side remains the same - about 100.

From my limited knowledge, it seems like I’ve got a problem with the compressor and likely need a new one. Is this correct? If so, what else should I replace at the same time? Or am I misdiagnosing this?
 
nm8shun said:
Hello!

AC has never blown cold as I’ve owned the car. Decided I need to fix it. Here are the details;
1. Fan blows in the cabin. But it’s not cold.
2. The compressor runs and the clutch engages (I can see it in the engine bay).
3. AC manifold gauges show 100 psi (low and high) in 90ish degree weather before car is turned on.
4. When car is on and AC is activated (fan on, snowflake button active), the Low Side drops to 80ish and the high side remains the same - about 100.

From my limited knowledge, it seems like I’ve got a problem with the compressor and likely need a new one. Is this correct? If so, what else should I replace at the same time? Or am I misdiagnosing this?
Click to expand...
You are spot on, your compressor is knackered!
The valves are not closing properly when it runs. It is providing virtually no 'compression', just spinning.

At rest your pressures are OK, 100psig on both sides is about average on R134a.
When running, with a decent refrigeration charge, you should have around 150 psig on the high side and 20 (ish) on the suction (low) side.

If it was a refrigerant issue and the compressor was OK, you would get very low suction pressures (down to a vacuum) and lower discharge pressures (high side) when running. Usually then the comp would cycle in and out on the low pressure switch.

The ONLY other thing it could possibly be is the expansion valve is staying wide open all the time. Highly unlikely and if that were happening you get liquid coming back to the compressor which would be evident by severe frosting of the low side (suction line) and that would destroy the compressor almost instantly.
 
enuff_zed said:
Zedebee said:
If all the hardware is working, maybe you just need a re-gas?
Click to expand...
What pressure is it supposed to be?
Click to expand...
I have absolutely no idea. Pondrew’s subsequent post shows how much I know about air conditioning systems compared to others.
 
Pondrew said:
nm8shun said:
Hello!

AC has never blown cold as I’ve owned the car. Decided I need to fix it. Here are the details;
1. Fan blows in the cabin. But it’s not cold.
2. The compressor runs and the clutch engages (I can see it in the engine bay).
3. AC manifold gauges show 100 psi (low and high) in 90ish degree weather before car is turned on.
4. When car is on and AC is activated (fan on, snowflake button active), the Low Side drops to 80ish and the high side remains the same - about 100.

From my limited knowledge, it seems like I’ve got a problem with the compressor and likely need a new one. Is this correct? If so, what else should I replace at the same time? Or am I misdiagnosing this?
Click to expand...
You are spot on, your compressor is knackered!
The valves are not closing properly when it runs. It is providing virtually no 'compression', just spinning.

At rest your pressures are OK, 100psig on both sides is about average on R134a.
When running, with a decent refrigeration charge, you should have around 150 psig on the high side and 20 (ish) on the suction (low) side.

If it was a refrigerant issue and the compressor was OK, you would get very low suction pressures (down to a vacuum) and lower discharge pressures (high side) when running. Usually then the comp would cycle in and out on the low pressure switch.

The ONLY other thing it could possibly be is the expansion valve is staying wide open all the time. Highly unlikely and if that were happening you get liquid coming back to the compressor which would be evident by severe frosting of the low side (suction line) and that would destroy the compressor almost instantly.
Click to expand...
Excellent reply!
And educational too. :thumbsup:

You feeling ok Pondy?
 
enuff_zed said:
You feeling ok Pondy?
Click to expand...
This wasn't me. Someone sober has hacked into my account and is posting useful things. Don't worry, I'm onto them! Normal bollox will hopefully resume shortly. :D
 
Thank you all. @Pondrew, especially thanks for the confirmation. If I could ask a bit more follow-up;

YouTube videos seem all over the place about what needs to be replaced. Scotty Kilmer seems to say you can get away with only replacing the compressor. The Car Wizard argues you have to replace *everything* (compressor, drier, evaporation, etc..). What say you? If the compressor is clearly the problem, should I just replace that, or are there other components that should be done at the same time?
 
nm8shun said:
Thank you all. @Pondrew, especially thanks for the confirmation. If I could ask a bit more follow-up;

YouTube videos seem all over the place about what needs to be replaced. Scotty Kilmer seems to say you can get away with only replacing the compressor. The Car Wizard argues you have to replace *everything* (compressor, drier, evaporation, etc..). What say you? If the compressor is clearly the problem, should I just replace that, or are there other components that should be done at the same time?
Click to expand...
It is good practice to change the drier/receiver while the system is empty and 'open', only as it has probably never been changed in many years. It isn't strictly necessary unless there is contamination in the oil (you will smell that; it smells horrible and acidic) which there shouldn't be on a car A/C as there are no electrical components in direct contact with any internal parts. It is generally electrical/ motor problems which damage the oil. Just check that any oil is almost clear and not brown (and doesn't smell of anything).

You don't need to change anything else, unless the compressor pipe fittings (or any fittings you undo) are perished. I am not sure if yours will have O-rings in the pipe unions. If it does, they really should be changed as they perish and can be damaged by removing/ replacing the unions.

Once the system is closed and sealed again, make sure it is well pressure tested (300 psig minimum), then a really good evacuation for at least 8 hours (only when there are definitely no leaks). New refrigerant is then added along with potentially a squirt of refrigeration oil.
A new (or refurbed) compressor should come with new oil inside, so adding oil may not be necessary. The refrigerant needs to be weighed in to the spec on the car plate. Car A/C is 'critically charged' with refrigerant, as they have a fixed expansion system so the correct amount will help prolong the life of all parts as well as work efficiently.
 
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