I've been doing a lot of work on my 1996 Blazer recently and it's been sitting still for a couple of months or more. I fired it up today and found the A/C blows hot. So I checked all my grounds and the wires going to the compressor as well as shorting the pressure switch next to the low side port valve. After shorting the connector the compressor turned on. I plugged it back up and used an old can of A/C refrigerant that my buddy had that has the gauge on it and found out that when the compressor was shorted the pressure dropped all the way to low. I added refrigerant until it read in the green and the compressor clicked on like it should. So I know there's a leak but I didn't know how bad it was. I let the car run for 10 minutes and low and behold the compressor started to short cycle, which means I have a leak somewhere. My question is, I've been reading things online about how if the system is contaminated it might cost a fortune or something for the local stealership to fix, so if I left it like it was and just didn't use the A/C since it's winter now, would it cause more damage or should I get it looked at as soon as possible? PS It's already been converted to the newer refrigerant, which was done a few years ago.

 

Sounds like a pretty serious leak. You can put dye in there and find out where the leak is but to fix it, you probably will still need a professional (vacuum and refill). Maybe best to bite the bullet now.

 

The system will cycle under normal operation as the cabin approaches the set point temperature because there is less load on the evaporator and the pressures start to drop. Its supposed to cycle under these circumstances. If it starts to cycle when everything is on full blast and the cabin is still 100F then something is wrong. The refrigerant oil that is used in modern 134a systems is very hygroscopic and once it starts absorbing water it forms acid and sludge which clogs metering tubes and kills compressor windings. How much moisture is getting into a system at zero pressure with a leak? Depends? Don't force a compressor to run when low on gas except to verify its the LP cycling switch because you can do damage to the compressor and a system low on charge will go into a vacuum on the low side and if that's where the leak is, pull in non-condensables, including moisture.

A leak is verified with a proper set of gauges. The leak is found with an electronic leak detector, a spray bottle of soapy water, feeling for oil residue around fittings and hoses, or as stated above, UV dye.


George

 

The hoses that go across the front are dry at the connections. The accumulator looks pretty dry at the connections. Where does it go when it goes in the black box after the accumulator? When I charged my AC I felt cold air coming out of that box right where it goes in. The orifice looks dry can't say anything after it goes into the same black box. The line to the condensor coil looks dry. Sounds like I'll have to use the dye.. I kept it on when testing the switch for less than 30 seconds so it should be fine.

 

Looking for leaks at connections is very subtle. The 134a turns into a vapor and disappears immediately but over time a small amount oil comes out with the leak and when you run your finger around the leaking connection you see a very small amount of oil.

The refrigerant flow is:

Compressor outputs high pressure hot gas
Condenser cools it and outputs less hot liquid
Metering (orifice) tube
Evaporator coils (in the black box)
Accumulator holds any liquid return and outputs only low pressure cool gas
Compressor increases pressure of returning gas where it heats up
Rinse and repeat

For any Nerds (or the cool kids that are just curious) reading this, the refrigerant cycle is described by the ideal gas law which in simplified form is PV=T or Pressure x Volume = Temperature and the science of phase change. When the compressor increases the gas pressure, the temperature goes up. When the condenser lowers the temperature, the gas changes phase to a liquid. When the metering tube lowers the pressure and the evaporator adds heat, the 134a changes phase again to a gas. When the work load of the evaporator is low and some of the liquid 134a remains, the accumulator holds it to make sure that only gas gets back to the compressor.

This only applies to our orifice tube system, systems with expansion valves use receivers in the liquid line.

Short answer to the OP's question, black box = evaporator coils in the cabin.


George

 

Would this be the cause of the leak? It's the only thing I could find. It had some oil on it and I sprayed it with soap. How would one go about fixing this?

https://streamable.com/vj8ufj

 

That's the low pressure cycling switch. It unscrews from the accumulator and a schrader valve is supposed to keep the system sealed. I always open these carefully in case the valve is stuck open. Sometimes when you take it off a little gas and oil can escape so if its been disturbed that might be the explanation. The spray bottle of soapy water should show bubbles if the system still has pressure and its leaking there.


George

 

Bubbles appear rapidly once sprayed and oil is all over the area. What parts do you recommend to fix this?

 

It depends on what is leaking. If its the pressure switch body then you unscrew it and screw in a new one. If its the schrader valve core then you remove the switch, remove the core with a special tool and screw in a new core. Its like a bicycle wheel. If there is pressure in the system then you either have to recover the refrigerant or use a special core removal tool which allows you to swap while there is pressure in the system. It is illegal to intentionally vent refrigerant into the atmosphere.


George