A/C Compressor Replacement and Pulley Alignment

[cwilson jr]

started working on getting my a/c running.  never have used it in the 7 years ive owned the truck.  all of the components are there.  i just installed the belt and now i'm troubleshooting.  nothing happens when i use the hvac controls inside.  i started with the low pressure switch and when i jump it, it turns on.

1.  so, i'm going to obviously get a new switch first, but when it kicked on i noticed the compressor pulley did something.  i'm not sure if it locked up, it seemed like the belt was still moving, but there seemed to be movement in the pulley and tension placed.  does the pulley engage and disengage and just get tighter when u turn it on?  makes sense, i just want to make sure this is normal and don't want to worry about snapping a belt.

2.  after i replace the switch, what would be my next steps?  i would imagine pull a vacuum using the air pump from harbor freight i see ppl using on here and then convert and fill with ref. and dye and check for leaks? 

[Jason S]

What year truck are you working on?  As far as operation, the 73-75 systems were a bit different than the 76-up system.   What refrigerant are you going to be using?  These trucks originally came with R-12, but that is usually expensive (unless you have a source who stocked up). Has the truck been converted to use R-134 at some point and was it correctly done?

Since you say you are jumpering the low pressure switch (i.e., cycle switch on low pressure side), I presume it is a 76-up variety.  The compressor clutch should engage whenever the switch is bypassed and the control panel in the cab is switched to a/c.  If you have low refrigerant levels, the compressor should not engage even when everything is connected normally. As for the belt question, you should check the compressor belt tension to verify that it is tight.

If the truck had been converted to use R-134, usually (but not always) there will be the R-134 to R-12 adapters threaded onto the R-12 fittings on the system.

You may not need to replace the compressor cycle switch if your system is low or out of refrigerant.  If you don't know what refrigerant and oils were placed in your system (i.e., is it still setup for R-12 or was it switched at some point to R-134 or something else), it would be a good time to have all the old oil and contaminants flushed out of the entire a/c system (condenser, evaporator, lines, etc.). 

Since the a/c system hasn't been serviced in a long time, it also would be prudent to replace the accumulator/drier to ensure that you don't have premature failure once everything is back together and running.

Once everything is cleaned and a new accumulator is in place  and proper amount and type of oil in place for desired refrigerant: Use a set of gauges and pull a vacuum on the system and completely evacuate all air. Turn off the valves and let the system set with vacuum. Watch the gauges when you turn off the valves and write down the vacuum.  Wait around an hour, go back and check the gauges. If there is no change in recorded vacuum and vacuum level after 1 hour, then you can begin to charge the system with refrigerant.

[cwilson jr]

this is on an 85.  r-12 system.  when i first had gotten the truck i remember placing the 134 adapters on and tried adding ref. to no avail.  it wasnt important then, so i never thought anything of it again, until now, where i would like to get it working for my disabled son.  i have purchased a new cycling switch and accumulator as of now, along with the following tools:

http://www.harborfreight.com/air-vacuum-pump-with-r134a-and-r12-connectors-96677.html

http://www.mastercool.com/media/91046A-Parts%20List.pdf

[DrDaryl]

If it is low on refrigerant the compressor won't cycle, so it may not be your switch.  Years ago I just added Freeze-12 to mine (you can still find it on ebay) to get it to function and it cooled just fine for quite a while.  To fix it right you will need to pull it all apart and flush everything, replace the orifice tube and the accumulator.  I would take the compressor off and drain the oil from it.  Then you could add the correct amount of oil to the system.  If you are going to go r134 changing the condenser to a parallel flow type (probably less than $100) will improve cooling in my experience.

[cwilson jr]

i have done everything you said except for switching condensors, which sounds like a good idea, but i have to wait on that and i didn't pull the compressor.  I already have everything flushed and put back together ready to vacuum.  now, the 134 conversion kit i have has a can of oil included in it.  at this point i don't want to really pull the compressor out unless it was absolutely a necessity.
after flushing the lines, cond. and evaperator, should there be enough oil still in the system or should i add the can of oil entirely, or partially?

i also noticed when i pulled the lineset off the rear of the compressor, it was bolted in correctly, but without any gaskets.  i purchased an o-ring set, but to me if there was to be gaskets there, they would have to be flat, so i left that as i found it for now.

update:  just evacuated the system and began to install ref. in.  once the compressor kicked in, the belt started squealing and smoking.  is my compressor bad?

[DrDaryl]

How much refrigerant was put in when the compressor started squealing?  If it was just a couple of cans, then yes I think the compressor may be locked.  On the other hand if you were nearly at a full charge it may indicate that the pressure in the system was too high--may need to set a fan blowing on the condenser or wet it with water, which will reduce the system pressure; or you could be overcharged.  Not sure about the gaskets on the compressor, but mine did have an o ring type gasket between the compressor and the hose manifold.  There is probably about 1 or 2 ounces of oil in the compressor.  I don't remember how many total for the whole system on our trucks.  You can get a wrench from auto parts stores that will turn the compressor, so you could take the belt off, let the system cool down and find out if you can turn it.  I'm no expert, just trying to help.

[cwilson jr]

i have put about 3/4 of a can i would say in there.  basically i stopped adding ref. as soon as the compressor kicked on and i noticed something wasn't right.

so, i'm thinking the compressor is locked from what i'm reading.  if i have to replace the comp. as its looking more like, what do i do about ref. and oil now? 

currently i am thinking about recovering the ref. i already put into the system, into an empty flush kit canister i have to salvage it, if thats possible or disposing of it entirely.  i know to fill the back of the new comp. with oil, so i would imagine that would take care of those two things.  if i'm right?  would i be alright from there or do i have to evacuate again?

i just paid to have it evacuated.  i have the $20 harbor freight air vacuum pump, but havent messed with it yet.

[Jason S]

With the engine off:  Can you turn the compressor (not just the pulley) by hand? 

[cwilson jr]

just inspected everything with the engine off.  the compressor doesn't turn, the pulley doesn't turn, the whole assembly is secured to the bracket all the way around tightly, and the belt is tight.  amazingly the belt still looks to be in good shape.

[Captkaos]

Will it turn without the belt on it?

[cwilson jr]

nope, she was locked up, replaced and we're good to go.

[cwilson jr]

now, only when the compressor engages, there is a "vibration" in the belt.  the belt starts bouncing, maybe up to an inch.  i'm concerned my belt will eventually break while using the a/c.  the only thing i notice is the power steering may be sitting ever so slightly on a slant.

i have the belt tight along with the compressor brackets.

is that normal for the power steering?  anyone have an idea of what would cause this?

[Captkaos]

So there is an alignment problem with the belt?  Are you missing brackets?  It will probably throw it before it breaks.

[cwilson jr]

its ever so slight, but that's the only thing i'm noticing.  have all of the brackets, i confirmed this and everythings tight.  if the ps is the cause.  is there a way to align it?  if it threw the belt, wouldn't it be chopped by the belt?

[bd]

now, only when the compressor engages, there is a "vibration" in the belt.  the belt starts bouncing, maybe up to an inch.  i'm concerned my belt will eventually break while using the a/c.  the only thing i notice is the power steering may be sitting ever so slightly on a slant.

i have the belt tight along with the compressor brackets.

is that normal for the power steering?  anyone have an idea of what would cause this?

The vibration you described sounds normal.  Four pulses per revolution are generated by the A/C compressor and imparted to the belt; the pulley spacing causes the belt to resonate at low RPM.  It was a design shortcoming.  You may need to tighten the compressor belt a little bit more. 

...have all of the brackets, i confirmed this and everything is tight.  if the ps is the cause.  is there a way to align it?  if it threw the belt, wouldn't it be chopped by the belt?

Can you post a pic of the 'belt alignment' issue?