Air conditioning doesn't work...what to do

[chinny4290]

Hey guys. I've tried a search but I just spent the last hour and it was all a bit vague and I'm still left scratching my head.

As far as I'm concerned, my AC is still R12. When I turn it on I hear a hiss in the dash but no cold air.


I don't know if it needs to be recharged....theres a tank-shaped thing in front of the radiator that I was told was part of the A/C, and there are a couple loose wires...

KNowing that R12 is near impossible to get or really expensivve.....how can I diagnose my A/C, know that it needs freon...or what not...and what are my best options?

A/C would be a nice thing when I drive my W116 because days can get real hot and humid here in NJ.

Thanks all.

[Big_Richard]

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[chinny4290]

Its low on gas is all - if you can hear a hissing sound, it just means the refrigerant level is so low that there isn't enough in the system for it to still be a liquid at the high pressure side of the TX valve on the evaporator. IE, its only a gas passing though it, and as the whole principal of the system relies on the phase change from liquid to gas to achieve any cooling, its just not going to work.

on your receiver drier, there should be 2 sensors, one 80c temperature switch for the thermo fan, and one refrigerant pressure switch, off the top of my head, i cant remember which one is which.

Would it be ideal to just change over to 134 than try and get R12?

[WGB]

What model  have you got and what type of A-C system?

If it is a V8 and it has the automatic system it is possible that the problem is in the controls.

Does the compressor cycle on and off?

If the compressor is cycling what is happening in the receiver-dryer sight glass.

Hissing sounds to me sounds like the system is alive - a flat system will not allow the compressor to work in most systems.

If the compressor does not cycle do this -

The temperature switch on the receiver-dryer is the top one. The lower one is the pressure switch - disconnect the two wires from the pressure switch and connect the two on the chassis wiring side together. If this causes the compressor to cut in you have a flat system.

Do not leave it running for too long whatever you find.

Bill

[chinny4290]

It's a 75 280S.

[Big_Richard]

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[allrock]

recharge the freon,if it gets warm again,have a leak test on the cooling coil,if its not leakin,check all the ,hoses and joints...

[chinny4290]

It's an R12 system though...

[oscar]

I think freon is R12.  That aside, the easiest way to tell what gas is in your system -
-R12 systems usually have the same size adaptors and aren't colour coded. 
-R134a usually are colour coded and have different sized adapters whereby the low side has a blue cap and smaller connection and the high side has a red cap and larger connection. 
-Also, r134a connections are threaded on the inside whereas the R12 connections are threaded on the outside.

Look at the following pics

R134a
LOW SIDE


R134a
HIGH SIDE



R12
High side pictured below and low side pictured bottom.  Note the "S" on the top of the compressor.  It means "suction" or low side.   Both fittings are physically the same



Having shown all that, you can go to an autoelectrician that you trust and get them to check it out, leak test the system and recharge with whatever gas you got (assuming the guy you go to has got r12 if that's what your system has)

Otherwise, you can check the system pressures yourself by by a manifold gauge set off ebay or auto stores like this HERE and even buy recharge kits off ebay or auto stores like this HERE

My 350's system had been previously recharged with r134a but was flat due to a corroded hose which I replaced from a wreck.   Then I found that the compressor's front seal was leaking too but it worked well over summer and I didn't have a vacuum pump which would've been handy but not necessary.  I decided to go with HR12 which is a flammable propane/isobutane mix and did it myself.  Never knew anything about a/c apart from what others shared so if you're game, have a go at recharging the a/c yourself. http://forum.w116.org/mechanicals/ac-setback/

[WGB]

If it is a 280S with original "York" Compressor and smaller Condensor than the V8's you will have to stick with F12 or use Hychill as apparently it doesn't change over to 134 gas well.

Considering the drop in A/C performance the V8's suffer with a change to 134 I wouldn't even bother with the thought.

I hope you find someone with some F12 (Freon) but it has been illegal to manufacture it since 1994 so supplies are dwindling.

Bill.

[johnnyhonest]

The temperature switch on the receiver-dryer is the top one. The lower one is the pressure switch - disconnect the two wires from the pressure switch and connect the two on the chassis wiring side together. If this causes the compressor to cut in you have a flat system.

Do not leave it running for too long whatever you find.

Bill


[/quote]

Does the car have to be running for this method to work or just having the key on will work???

[WGB]

Yes the motor has to be running to see if it works.

If you turn on the ignition without the motor running you should hear a click from the compressor clutch if it is pulled in.

Here is a photo of a 6.9 receiver-drier with the switches labelled.



The contacts for the switch are under the rubber cap an if you short them together it should make a low pressure system start.

Bill

[johnnyhonest]

Thanks Bill!

[johnnyhonest]

Here's a dumb question.  The Freon fill kits that I see on eBay have a hose and fittings but no gauge.  How do I know when the system has the proper amount of gas???  I'm guessing buy a gauge???

[oscar]

You guess basically by adding up the can charges.  Say your system is empty and bone dry, you need 2.2lbs to fill and the cans are 12oz.  You'll make it up by using 3 cans of freon and 1 can of oil.