1992 940 AC question

Hamiltonhiii · Post by **Hamiltonhiii** » 03 Aug 2009, 15:28

It all started with a leak, and now that I've changed two pipes and the condensor, my compressor died. Or did it? It turns and doesn't appear to be freezing, but how do I know it's not the dryer that's causing my problem? It doesn't cool even when I first turn it on....and I'm about the swap out the compressor (but was told it might be my dryer by my brother).

Post by **billofdurham** » 04 Aug 2009, 15:50

Your compressor died but it still turns? Are you turning it by hand or using a jumper cable to kick it into life?

My first check would be the refrigerant charge - too much or too little will stop the compressor.

Bill.

Hamiltonhiii · Post by **Hamiltonhiii** » 04 Aug 2009, 18:45

Ok, the charge is right on the money. It's been tested for leaks and it's tight. It stays right where it needs to, but then when I engage the AC it falls below 70 pounds (I'm not sure where it's supposed to be when it's at rest- my AC technician did that part). I'm pretty sure these levels are correct.
The compressor turns as normal when you engage the AC but won't cycle off - and there's no cold air.
I'm sorry, I guess I should have given more of these details from the start.
h

Post by **billofdurham** » 05 Aug 2009, 12:16

The attached shows some of the things that can cause the problem you are having:

940 AC trouble shooting.pdf: (17.02 KiB) Downloaded 163 times

One thing that isn't covered is the radiator cooling fan. If that has stopped for any reason then the AC will shut down due to excessive heat.

Bill.

Hamiltonhiii · Post by **Hamiltonhiii** » 05 Aug 2009, 12:40

Ok, thanks.
I'll check some of these items out and get back to you.
Does the dryer "freeze up" like I've heard of some cars doing?
h

Hamiltonhiii · Post by **Hamiltonhiii** » 05 Aug 2009, 12:42

And I'm sorry Bill, I'm just a rookie really....what's an expansion valve?

Post by **billofdurham** » 05 Aug 2009, 15:47

I'm just a rookie really....what's an expansion valve?
And I'm sorry Bill, I'm just a rookie really....what's an expansion valve?

I was going to blind you with science but I know what it's like to be the rookie so this is from Wikipedia:

A thermostatic expansion valve (often abbreviated as TXV or TX valve) is a component in refrigeration and air conditioning systems that controls the amount of refrigerant flow and the superheat at the outlet of the evaporator. This is accomplished by use of a temperature sensing bulb filled with a similar gas as in the system that causes the valve to open against the spring pressure in the valve body as the temperature on the bulb increases. As temperatures in the evaporator decrease, so does the pressure in the bulb and therefore on the spring causing the valve to close. An air conditioning system with a TX valve is often more efficient than other designs that do not use one.

A thermostatic expansion valve is a key element to a refrigeration cycle; the cycle that makes air conditioning, or air cooling, possible. A basic refrigeration cycle consists of four major elements, a compressor, a condenser, a metering device and an evaporator. As a refrigerant passes through a circuit containing these four elements, air conditioning occurs. The cycle starts when refrigerant enters the compressor in gaseous form. The refrigerant is compressed by the compressor to a high pressure and temperature state. The high pressure and temperature gas then enters the condenser. The condenser changes the high pressure and temperature gas to a high temperature liquid by expelling heat either to the ambient air or a fluid similar to the action of an automotive radiator. The high temperature liquid then enters the expansion valve where the valve acts on the refrigerant and changes it to a low pressure and temperature liquid. The low pressure and temperature liquid is now suitable for cooling. The low temperature and pressure liquid enters an evaporator in which heat is absorbed from the air or another fluid and the cooling action takes place. After exiting the evaporator, the refrigerant is now a low pressure gas. The low pressure gas enters the compressor and the cycle repeats.

If the expansion valve fails the system will shut down to protect itself.

When the AC is switched on does the radiator fan kick in as it should? The AC and the fan are interlinked to provide as much cooling for the condenser as possible. This is the second thing to check after the state of the charge of the refrigerant. Basically the AC system works by the gas being compressed, condensed into liquid and returned to a gas in a continuous cycle. It is the change of state from liquid to gas which achieves the cooling, and if for any reason there is insufficient air passing through the front radiator/condenser then the gas will not change state but remain as a hot, high-pressure gas and will complete the circuit back to the compressor still as a gas and there will be no cooling.

Bill.

Hamiltonhiii · Post by **Hamiltonhiii** » 05 Aug 2009, 16:22

Bill:
Whoa, Dude.

That's the best explanation I've run across of my AC system. I have some checking to do. Right now, I have evacuated the gas in order to put on a new condensor, but I'll look into this and get back to you and your thorough self.
Thanks again.