Mod for cooling compressor?

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danielsantos

Member
Joined
Oct 20, 2013
Messages
24
Hello!

Here in Texas, my compressor often overheats when I'm stuck in traffic, shutting down the AC when I need it the most. When I put my hand on it, I've noticed that the compressor gets fairly warm even on mild days and that it has no cooling system. Is there an existing mod for cooling the compressor I could buy? I was working on designing one when somebody at Dallas Makerspace suggested I see if there was already such a mod I could buy! (DUH! that would be easier!)

I would prefer to exploit the high-voltage cooling system, so that's the route I was looking into. Of course, I haven't had the freon level checked -- I should probably do that as well.
 
Hello!

Of course, I haven't had the freon level checked -- I should probably do that as well.
That is the 1st thing that should be done.
On an A/C system the returning refrigerant should be cool, near freezing, there shouldn't be any need for cooling system to be added. A system that is low on refrigerant, the returning at much higher temps.
 
Hello!

Here in Texas, my compressor often overheats when I'm stuck in traffic, shutting down the AC when I need it the most. When I put my hand on it, I've noticed that the compressor gets fairly warm even on mild days and that it has no cooling system. Is there an existing mod for cooling the compressor I could buy? I was working on designing one when somebody at Dallas Makerspace suggested I see if there was already such a mod I could buy! (DUH! that would be easier!)

I would prefer to exploit the high-voltage cooling system, so that's the route I was looking into. Of course, I haven't had the freon level checked -- I should probably do that as well.
I am in Houston. Most of my driving is at low speeds, including some stop-and-go. I have not noticed the AC compressor stop working. As has been suggested, check the refrigerant level.
 
FWIW, my AC does the same: shutting down after running a while in extreme heat, high 90s or more. (The "climate control" power draw would show zero when it normally shows some power draw, however small, when the AC is on.)

Anyway, I wonder how much cooling the compressor will help. The compressor compresses the refrigerant in gas form back into a liquid. The compression process adds heat. (It's the reverse of the evaporation of the liquid refrigerant into gas form which lowers its temperature.) The hot refrigerant liquid (under pressure) then goes through the condenser (a "radiator"; a heat exchanger) to be cooled down before going into the evaporator again.

If the condenser gets too hot e.g. when the car is in stopped or stop-and-go traffic, the liquid refrigerant does not get cooled sufficiently, I suspect a temperature sensor or pressure sensor somewhere would shut down the compressor at that point since it'd be pointless to keep trying at that point.

So cooling the compressor will probably help, but the other part of the compression cycle, the condenser, needs to be addressed as well.

(I explained in more elementary terms not because I think anybody here needs it, but more for posterity, for random future folks.)
 
In the "good old days" compressors were controlled with snap action switches for pressure and/or heat. Now it is done with transducers, that relay the refrigerant pressure to a micro controller that takes a bunch of variable inputs and compares that to its operating "map" that is considered normal or at least not detrimental, and if outside these parameters, shuts down the system to prevent damage.
You can't just "jump" some switch and get it working. You need to address why it is out of parameters. It might be, just low on refrigerant, but the returning temp is too high and the system shuts down to protect the compressor. Solve the problem and the symptom goes away.
New car systems use much less refrigerant than the old days with fixed displacement compressors.
Given to cost of a new compressor, I would have the system pulled down, oil quantity checked and topped off and recharged. Much cheaper than a whole new system if the compressor starts shedding metal.
Oil is moved with the refrigerant, so any loss of refrigerant also means a loss of oil.
Price out just the cost of a scroll compressor for the Leaf, and a few bucks in preventive maintenance looks cheap.
As I pointed out my 1st post, the returning refrigerant in a properly working system will be just below the freeze temp of water (32 deg F) so nothing you could come up with would have the least effect (be any cooler than ambient). If the system is working properly, it has all the cooling it needs from the returning refrigerant.
 
The air conditioning condenser is cooled by the same coolant that cools the motor, inverter, charger and battery. If it shuts off in stop and go traffic, maybe your radiator fan isn't working.
 
The air conditioning condenser is cooled by the same coolant that cools the motor, inverter, charger and battery. If it shuts off in stop and go traffic, maybe your radiator fan isn't working.
This is incorrect the Leaf uses a air cooled condenser just like a conventional car. The coolant that cools the inverter is a separate system. Unless you mean the air entering the front of the car is the same air that also passes through a separate radiator for the inverter. But that is not what you wrote.
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From the Leaf service manual.
 
To add to this discussion, the Leaf cooling system (heat pump) has various levels of power usage. If anyone has every watched it under LeafSpy for example, when traveling at speeds lower than 15 MPH, it limits the power usage to 1500 watts, when traveling over this speed, it can increase it all the way to 4500 watts. It's equally possible to get the system to "freeze" as I've done this a few times myself.

This can happen when driving in stop and go traffic. It's really hot outside, so the system wants to run at "max" basically, but when you are moving slowly (under 15 MPH), the system limits to 1500 watts, which may not be "enough" cooling. When traffic picks up and you get over +15 MPH, so the AC kicks into high gear which means the air gets really, really cold fast and then you slow down again under the speed and it drops the AC power down to 1500 watts again. Do this enough times and you can get the AC to "freeze" over which makes the whole thing shutdown until it thaws out. In hot weather, it can reset after a few minutes, but you get an annoying couple of minutes of no AC when this happens.
 
I spent some time poring over the service manual's section "HA". (Note: NOT "pouring"; it's one of my huge vocabulary pet peeves!). The compressor will stop running if:
  • Refrigerant pressure is over 384.3 psi or below 20.3 psi.
  • If the air passing through the evaporator is below 1'C / 34'F.
The refrigerant pressure sensor is at the outlet of the condenser. (All of the above is on page HA-28.)

I can see a case where things get so hot that the compressor and condenser fail to turn gaseous refrigerant back to liquid, resulting in a refrigerant pressure outside of the prescribed pressure range, leading to the compressor being stopped.

That conjecture also fits my observation that after driving a while with the AC off, the AC will work again, because the condenser and/or compressor would cool down enough to start being effective again.
 
All automotive A/C suffers from less than ideal Condenser conditions. On some of my custom builds I oversize the condenser in terms of rated BTU rejection, and the results are quite an improvement in system performance and the resultant lowering of head pressure makes the systems last.
Driving in 100 deg F weather and still being able to reach the frost point on the evaporator is the proof.
If your system is tripping high pressure safeties, look to why, it may be the condenser is degraded, fins may have lost their thermal bond to the tubes, changes made to the air flow (air dams added, etc).
 
I spent some time poring over the service manual's section "HA". (Note: NOT "pouring"; it's one of my huge vocabulary pet peeves!). The compressor will stop running if:
  • Refrigerant pressure is over 384.3 psi or below 20.3 psi.
  • If the air passing through the evaporator is below 1'C / 34'F.
The refrigerant pressure sensor is at the outlet of the condenser. (All of the above is on page HA-28.)

I can see a case where things get so hot that the compressor and condenser fail to turn gaseous refrigerant back to liquid, resulting in a refrigerant pressure outside of the prescribed pressure range, leading to the compressor being stopped.

That conjecture also fits my observation that after driving a while with the AC off, the AC will work again, because the condenser and/or compressor would cool down enough to start being effective again.
I have run into cars where the set points for the safeties are different if the vehicle is in motion or stationary. A lot of what was once hard and fast snap switches are now variable set point transducer controls.
385 psi is a condensing temp of 180 deg F. With the std of condensing temp being 40 deg F above the air passing through the condenser. The system should be good to 140 F day. The closer you can get the condensing temp to ambient the better, the 40 deg f above is considered the max acceptable compromise. I have seen my systems in the high teens, low 20's above the ambient.
If you don't shed the heat at the condenser it just gets cycled back to the evaporator.
If you are tripping the high pressure safety than you are not shedding the heat. It may take a new condenser to solve the issue, but a new condenser is cheap compared to a damaged compressor, or a system that is continually run hot.
 
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