Fixing the A/C in my 1987 Comanche. How Cold Will it Get?

[NEO auto]

I have a 1987 Comanche with air conditioning.

It blows out somewhat cool air, but on a hot day, it is not near cool enough.

 

My question is, does the factory air conditioning get pretty cold?

 

I bought an A/C recharge kit, and the employee at the parts store said it should fix the problem.

He showed me under the hood where to plug in the recharge kit (See pic with location circled in red).

 

I'd hate to use this recharge kit and still have the same air temperature (It was expensive).

 

I'm willing to give it a try, but could it be there are other factors at play?

 

Thanks for any advice.

 

 

 

 

 

[rylee144]

How much was it? This is 75 and this thread explains it. If it works for you.

 

 

[Minuit]

STOP! DO NOT USE THAT RECHARGE KIT!

 

AC repair is not something to be taken lightly. At a bare minimum, you'll need a set of manifold gauges. You need to know what's in that system. This is something that you really need to be willing to do properly and cleanly, otherwise you will make things worse. If you aren't willing to read up and do it properly, find an AC guy that knows how to do it right, and I'm not talking about someone who just knows how to push buttons on a Robinair machine.

 

Why is the recharge kit bad? It contains stop-leak and who knows what else. Stop-leak will plug up the tiny orifices that system relies on to operate. You do not want anything but refrigerant, the proper oil, and maybe some dye in that system. It also has no way of telling you what the high side pressure is. If there's a leak, it needs to be fixed properly. If the system has been in use for several years and hasn't been recharged in that time, you may very well just need a simple top-off. But you have no way of knowing that for sure. What if the system is already overcharged? You put 20oz of refrigerant and stop-leak in that system, you're going to have a bad day.

 

I'm away from my PC now. I'll type up more details later. If you're willing to learn the correct way to do things, I'm more than willing to help. But for the love of whoever you regard as holy, do not put that recharge kit into your system.

[Minuit]

Alright, more details as promised.

 

I do not like stop-leak in any form, be it for A/C or transmissions or engines or whatever. You aren't really fixing an A/C system by putting a stop-leak chemical in it. Find the problem and fix it properly, or don't bother. In the short term, you're degrading performance (the stop leak $#!& takes the place of refrigerant), and while it may stop the leak in the short term, it is NOT worth the cost. In the long term, it will RUIN your system. I personally will not touch any automotive A/C system that has been "stop leaked". From that point on, it's tainted and needs to be either flushed or replaced. That crap can plug up things in the system and create restrictions. In particular, the expansion valve - the part that gives you cooling. High pressure refrigerant flows through a tiny orifice, in the process reducing in pressure.  That orifice is REALLY small. What if the stop leak chemical decides to solidify in the expansion valve and deadheads the compressor? They say it doesn't, but that's not a chance I'm willing to take.

 

If you're willing to learn and take this on properly, find yourself a set of manifold gauges. I think you can rent a set at most auto parts stores. They won't be great, but they'll be good enough. The manifold gauges will allow you to see a fuller picture of the system's operation. At best, a "recharge kit" only has a low side gauge, and that won't tell you much about how the system is performing on its own. You really need manifold gauges to do this, I can't stress it enough.

 

Your system was retrofitted from R-12 to R-134a. These conversions are usually half-assed at best, but I have no way of knowing since I can't look at your truck. A/C compressors are lubricated by having oil mixed in with the refrigerant. R-12 used mineral oil, which does not mix with R-134a. Hopefully, they replaced the oil when they converted it. If not, your system ain't gonna work for long. If it's worked for a decent amount of time on R-134a, you're probably ok.

 

If I was working on this, before doing anything else I'd want to drain the compressor and replace the receiver-drier just for purposes of changing out some oil (and seeing what type of oil is in there), as well as finding out if the compressor is full of junk. You can grab the very front face of the compressor and give it a spin. If it rotates smoothly without any "hard spots" in the rotation, the compressor is likely in good health inside, or at least it hasn't been completely turned to glitter.

 

Before you put hands on it, you need to do some reading on A/C system theory. To do any of this work from a well informed point of view, you need to understand how it works. If you really want to understand it, there is a lot of math involved. I learned it in college, but I've probably forgotten it all by now.

 

Here's a good but high-level explanation of it. Lots of thermodynamics jargon: http://www.evanstempcon.com/pdf/Air_Conditioning_Theory.pdf

 

Here's just what you need to know. There are several pages to read through on the right side of the page. Also, MJs have a receiver-drier located in the high side of the system just before the expansion valve. It just acts as a reservoir, and contains desiccant that can help get any last bit of moisture out of the system if it wasn't vacuumed properly: https://swtc.edu/Ag_Power/air_conditioning/lecture/basic_cycle.htm

 

Step One: Diagnosis with manifold gauges

This step is just to see what's going on. You're not putting anything in yet, just seeing how the system behaves by looking at pressures. Don't add anything yet!

 

Make sure both valves on the gauges are closed, and the hose fittings are all tightened. You should be wearing leather gloves and eye protection. If refrigerant spits out, it can give you frostbite in a split second. The gauges will have quick connectors on them that mate with the ones connected to the compressor. The bigger one is the high side (red) fitting. The smaller one is the low side (blue) fitting. They should snap on just like a hose connector. Make sure they're fully seated and that the "collar" has clicked!

 

Static pressure: with the system off for at least an hour or so and the engine cool, this number should be roughly equal to the ambient temperature in Fahrenheit and equal on both the high and low sides. It should be marked on the low-side gauge. There is one correct number that this should be, and if it isn't that number, there is a problem. If this number is too high, the system is contaminated. If the number isn't equal on both sides after the system has been off overnight, the system is restricted. If it's too low, there is most likely so little refrigerant left that the compressor wouldn't kick on at all, or it would immediately turn back off.

 

Once the gauges are hooked up and you've taken a static reading, start the truck up and turn the A/C on. Watch the gauges as the system works. You might hear the compressor clutch kicking on and off - that's normal, as long as the compressor doesn't kick on and immediately kick off again. Play with it a little bit. Rev the engine up and see what happens to the pressures. Watch what happens when the compressor kicks on and off.

 

Running pressures: These should roughly correspond with the temperature. Here's a basic chart of roughly what you should be looking for:

 

Here's my truck with the compressor running and an outside temperature of about 75.

 

If the running pressures, especially the high side pressure, is lower than what you see on the chart, and the system hasn't been recharged in at least a couple of years, then you most likely just need a top-off! But you don't know this until you see the system running with gauges hooked up. If the system needs to be recharged every few months or less, there is a leak that will need to be tracked down.

 

If it's very much higher than the number on the chart (a little too high is fine, these are rough numbers), there are a few possibilities, and none of them are fixed by stuffing more refrigerant in it.

 

- You have a restriction. The most likely readings are a very low (maybe even vacuum) low side pressure and a very high high side pressure. If the system cools at all, this is probably not happening.

- The system is overcharged. The charge needs to be evacuated and a proper charge needs to be weighed in.

- Insufficient airflow through the condenser, or poor condenser performance. If the pressure comes right down if you spray some cool water on the condenser, this is your issue.

 

If you're willing to get your hands dirty in automotive HVAC, rent a set of manifold gauges and tell us what the pressures look like.

 

I don't like any of the Youtube tutorials I've seen. They always seem to get something wrong. I wish I had a good resource to add for more reading, but right now I'm having a hard time coming up with one. I read a well put together guide on some car forum years back, but I don't remember where or who wrote it.

 

 

 

To answer your actual question, the A/C system in my 91 is an exact copy of the R-134a system used in a 1996 Cherokee. As a first generation R-134a system, it'll never be as good as an OG R-12 system that's still using R-12 or what they have now, but I'm very satisfied.

 

[Strokermjcomanche]

In addition to the above , you really should have a/c lines /hoses designed for R134a . 

[AZJeff]

43 minutes ago, Strokermjcomanche said:

In addition to the above , you really should have a/c lines /hoses designed for R134a . 

That is not automatically a requirement when converting an R12 system to R134a.

 

While the newer hoses do have a barrier membrane in them to prevent leaking of the smaller R134 molecules, it’s well known that old R12 hoses that have been saturated with R12 type refrigerant oil are pretty sealed from R134a leakage.

 

On a 25+ yr old vehicle that had working AC most of its life, the oil saturation potential is pretty high.

 

Otherwise, the comments from “Minuit” are pretty much spot on.