I once read that one could remove the temp sensor from the coolent line to make the air conditioning work better. I seem to have lost my freon over the winter, so I thought it would be a good time to do this. I searched for the thread but couldn't find it again.

 

Air conditioner no worky too!? Classic crank position sensor problem - you have all the signs: no charge, no cruise, and no a/c. If you had an automatic you wouldn't have OD either.

 

I should have checked that. A few years ago I lost a serpentine in the freeway which acted like a weed eater from hell and cut my crank position sensor wires (also trashed my hood insulation and caused an oil leak somewhere around the timing cover, haven't been able to track that one down). I don't think I checked the gap after that.

Back to the post, anyone remember the temp sensor trick?

 

The part going into the tube is the temp sensor. Pulling it out just makes the system not know how cold it is and leaves the compressor to run longer...which means colder.

I would think this would raises pressures, put more strain on the compresor and lessen it's life expectacy.

Den

 

I haven't gone and looked, but I imagine you're talking about the AC systems Thermostatic Expansion Valve sensor.

Pulling that from its well would make the valve think the evaporator coil is low on boiling freon (As the coil fills, the the freon level approaches the coils outlet. In doing so, the outlets temperature drops as an indication of same. The TXV sensor sees this and throttles back on the flow).



I would recommend you NOT do this as;

1) You risk destroying the compressor by flooding liquid freon to it (you can't compress a liquid).

2) You risk destroying the compressor by washing all the oil out of it. This happens as the liquid freon mixes with the oil, goes to boiling, and causes the oil to foam. This foam (if it doesn't bust the compressors valves on the compression stroke), is pumped out of the compressor. No oil! Goodbye bearings!

2) The AC system's performance would most likely drop due to the fact you're removing a great portion of the pressure differential required to make the freon boil. If you can't induce the freon to boil, it can't absorb heat.



Refrigerant circuit (typical):



During normal operation, the condenser coil is the high pressure side of the circuit. The evaporator is the low pressure side of the circuit. The compressor and TXV are what keeps them separate.

The TXV pee's a small amount of liquid refrigerant into the evaporator coil. The compressor sucks the gaseous freon from the evaporator. In doing so, the pressure drops on the liquid freon still in the evaporator. Due to the characteristics of the refrigerant, it MUST boil at a given pressure/temp (laws of thermodynamics). In order to boil, the liquid freon MUST absorb heat (it gets that heat from the cabins air).

By allowing the TXV valve to go full open, you greatly lessen the pressure difference. That in turn screws with the pressure/temperature curve of the refrigerant. You threaten the compressor with liquid refrigerant.

Unless Dodge is doing something weird, the compressor's cycled by means of a low pressure switch in the suction line. When the pressure drops, it turns off the compressor.


The bottom line? . . . . . . . . DON"T!


BC (15+ years HVAC&R)

 

You ROCK dude!
I had the thing converted to R134a because of Al Gore, but it really doesn't seem to cool well. I bought a new expansion valve thinking the old one was sticking, but haven't replaced it yet.

Any ideas of what I should look for?

 

R12 and R134a have similar pressure/temperature curves. That and a similar BTU capacity for a given quantity of liquid refrigerant. The fact the R134a requires a synthetic oil [as compared to R12 using a mineral based oil. (The refrigerant must be capable of blending with the oil while having no side effects like boogers of gum forming)] prevents R134a from being an absolute drop-in replacement for R12.


Note I said similar characteristics. The differences present as a reduction in cooling capacity in this particular application when compared to one another in the same hardware.

 

When I have to convert anything from R-12 I have chosen to use one of the many "Drop In" subsitutes that are avalible on the market today. Have used R-406, R-409 and the Hot Shot brand. It is not as much of a hassle to convert. I found that with R-134 the cooling system needs to be in top condition and usually an auxillary fan is a help. And the evap. temps are not as low as R-12 meaning the air will not be as cold. This is at least in my experience.
R-12 is still availible if you have the proper license. I live in California and I have a EPA ticket Technician Type l,ll,lll. They still sell R-12 at Pep Boys here in town but the price for a #30 drum is $1,200.00 That is right and the decimal is in the right place. I still have some 12 ounce cans I had bought back in 1970 and the price tag was $.49
Last #30 drum of Hot Shot I paid somewhere around $50.00 last summer.
Another thing with the drop in gasses and R-134 is that you DO NOT fill the system till the sight glass clears like days of old. You only charge a percentage usually around 80% but some are a bit diffrent. A good scale is important. This is a real pain especially on auto units because there is always a slow leak through the seals and it permiates through the hoses. So when it gets low you don't know how much you have to ADD so you have to evacuate it and recharge it.

Last summer when it was 107*-108* here we were going on vacation to Big Bear and just about when we got to Ontario the A.C. went out so I pulled off into the Home Depot parking lot and I checked it out. The compressor was not running even though the blower was, if I jumped the compressor it would work. I traced it back to the compressor cycling switch that is mounted on the H valve where the lines enter the firewall. The electronics shorted out. This cycles the compressor on and off to maintain the desired temp. But I needed some fix and now. I went to a Auto Zone and I got a imitation Bosch relay they sell for foglights and some wire. Then with the parts I always carry in the truck, I bypassed the cycling switch wiring and installed the relay to switch fused battery power directly to the compressor clutch. The pilot on the relay was then triggered by the wire disconnected from the compressor. Doing this allowed me to still operate the compressor by using the temp switch on the dash. I did not want to pass all of the clutch current through the switch contacs on the temp slider. (this is why I think the cycling switch burned out, there is a little tiny DIP style relay that is potted into the case). and the clutch draws a few amps through this not to mention the sizable spike when the field collapses.
Now the AC works fine, infact it is better than fine because it gets so cold in the cab you either have to turn up the WARM of put on a jacket. You are now controlling the cycling of the unit yourself.
*Also if your AC is not really cold, be sure the hot water valve is shutting off, not the actuator moving but really shutting off.
and now might be a good time to clean all of the leaves and trash out of your air box inside by your passenger's feet. I have also sucked in paper napkins, plastic bags and some things that must have bumped out of my glove box.
This is just what I did. Jim.
*Things I still must do. (Thinking out loud)
I still need to install a relay to disable the air conditioner when the defroster is on this really gets me because when my windows are fogged up, I am usually pretty cold as it is.

Used to work on the transit busses years ago, the AC's were in the 20-30 ton range. Most used a 5 cylinder Trane or Carrier compressors and the evaporator coils were A coils 2 1\2 foot by 6 foot in size. The compressor was driven usually by a 4 cylinder Perkins or Kiki diesel engine and the air had to be tempered by upto +195* so it would be bearable and not be like being in a deepfreeze. The usual freon charge was around #30 of either R-22 on the Trane and some of the Carrier used R-500. The overkill was so you could keep the cabin temprature at a constant say 65* with the doors always opening and closing and 40 to 60 bodies at 98.6* moving in and out. If the air was not tempered it could freeze all of the people SOLID.
Just a bit of probably useless trivia. Jim