The A/C on my 77 worked great till this year. And now the clutch on my A/C Compressor is not engaging. Could it be the freon or compresser oil is to low???

 

If you are leaking freon, your compressor will not engage-- there should be a low pressure.
cut off switch.

Was it working at one time and sloooooowly got less cool?

 

Yep, It worked fine last year, then it started going to S#$$%.

 

Most of us don't remember this but it was normal to have to top the freon in the 70's and 80's.
Do you know if it's converted to 134a or still r-12?
Easy to top off yourself if 134a.

 

You can just by-pass the pressure sensor for a moment and check wether engaging or not.

 

Its converted to R-134.....

 

How do it By-Pass the Low pressure sensor..

 

Someone that has a 1977 can tell you exactly where the switch is located. The switch will be either on a larger diameter a/c line (low pressure side),or on the accumulator. Disconnect the two wire connector and jump a wire across the terminals. Start the a/c and the compressor should engage.
Before doing this I would hook up a manifold gauge set to the low and high side ports. If there is pressure in the system then it may just need some more freon. By jumping the low pressure switch, starting the compressor will enable the system to suck in the freon.
If the system still has the original hoses, then some loss of R134 can often be expected.

 

I would probably not mess with by passing the sensor-- the unit was working last year.

If the system has old R12 components on it, the 134 will leak out at a steady rate..

I'd charge the system (which will need it anyway) and I'll bet a dollar to a donuts that the system pops right on.

 

Just get a can of 134a and charge it up. You can get a can now that has the pressure gauge right on the can if you're concerned about the pressure. Otherwise charge it until the compressor runs continously on max, and the vent temps drop to 50* or lower.
If you overcharge it there is also a high side pressure switch and it will kick the system off and you'll not be able to cool the cabin very well.
A good way is with a gauge set and a 30lb can of freon.
Here is one at harbor freight;
http://www.harborfreight.com/ac-r134...set-60806.html

The problem with the gauge set is it does not have a way to connect the small cans of freon to it.
At auto parts stores or places like walmart they have setups like this.
http://www.walmart.com/ip/FJC-FJ6036...reons/25552411

Allows you to monitor the low pressure side and fill with the same hose. You just have to shut off the can periodically to see what the low pressure side pressure is, then open it back up to continue filling the system until the pressure is in the green arc and it can be used over and over vs the cans with pressure gauge on them, which are 1 time use setups. I fill mine to 25 to 35 psi which is slightly lower than most green arcs show on a gauge.

It depends on the ambient temperature at the time you are filling as to what pressure you are going to see. Also if running stock clutch fan be sure that engine is warmed up a bit and that you idle it up a bit, maybe 1200 rpm or so.

Do a search on youtube for, "topping off freon for a car" or similar. There are lots of them on there.

 

Someone told me that if the A/C clutch is not going on, it won't suck in the Freon. I'm going to need to by-pass the low pressure switch, to get the clutch to engage. Then hook up the cans...

 

In my earlier reply I suggested jumping the low pressure switch and then adding freon. Several others suggested just adding the freon. With the system having some pressure, I found it very difficult to add any freon without the compressor running to suck in the freon.

 

Here is the deal on that.
Your low pressure switch is not being made due to low pressure. That is about 25 psi or less.
The charging can will be around 60 psi.

So as soon as you open the can to charge the low side, compressor running or not, the low pressure switch see's the 60 psi and kicks on.
No need to jump the switch.

The compressor may draw the pressure below the 25 psi again and cycle off, but again as soon as the pressure rises above 25 it will turn on and will continue in this manner until a constant 25 psi or greater is maintained.

 

I just had my R134 '82 evacuated and recharged after replacing the main AC hose. The clutch kicked in as soon as the first can was opened up, and it cycled on and off until the charging was nearly complete.

 

If you put the can in some hot tap water it will empty way faster.