Help with this non-Mercedes A/C question appreciated...... - PeachParts Mercedes-Benz Forum

DieselHead · #1 06-11-2002, 04:57 PM

I have a 1994 Toyota Landcruiser that had developed weak A/C air. So, I decided to buy a few cans of R134 and charge it myself. The first can went in pretty well, but then during the second can, the A/C started cycling on and off pretty rapidly (it would stay neither on nor off for very long). What have I done wrong? Can I remedy this by adding more? Have I added too much? (I was told that the capacity in this car was pretty large) Thanks so much for this help. I promise I'll try and stick with Mercedes related questions next time. I participate in this Landcruiser only forum but they're not usually too helpful.

Alex

tcane · #2 06-11-2002, 07:08 PM

First, I am not familiar with your specific AC system. I do know that many cars, including many Japanese, cycle the AC compressor on and off to prevent the system from getting so cold that ice forms. I've seen some systems cycle 3-4 times per minute and others more than that. You will need to check with an AC manual for your Toyota to find out more. Check the public library for info, many contain a wealth of info about M-B cars and other brands especially the Mitchell line of manuals (the best AC repair info for M-B I've seen).

M-B diesels up to 1985 (I have little experience with the later models) use an expansion valve with a temperature sensor to prevent icing - when the temp is too low, the expansion valve opens and the pressure lowers until a specified point, and then the expansion valve closes.

Good Luck!
Tom

#3 06-12-2002, 05:50 AM

Japanese vehicles will cycle rapidly like that if the system is very low on refrigerent. Somplace under the hood there is a black or silver colored item the shape of a soda can with two silver aluminum lines coming off from it. On the top there should be a 1/4 inch diameter "eye", clean off the top of it and shine a light on it while the ac is running. With the compressor actually running you should see basically nothing. If you see bubbles then the system is low on r134a, add more to it per the directions on the bottle. I'm assuming that those cans only fit one of the service ports on the vehicle. Do you know if it is the low pressure side or the high pressure side.

Let me know how you make out.

Tom Sweeney · #4 06-12-2002, 08:58 AM

Alex,
I am not familiar with your particular vehicle. Checkout http://batauto.com it is an automotive air conditoining site that I am a member of. If you post there, someone probably has knowledge of your application.

Tom
82 SD
86 SDL

DieselHead · #5 06-12-2002, 11:11 AM

Brandon,
What's strange is that this only started after I added over a can of R134. Before I did it, the A/C acted normally, although it didn't cool very well. What I am afraid of is adding too much. I don't want the system to explode on me. But if you're saying that it's still not enough, I am willing to go add a third can.

Tom,
Thanks for the info on the website. I'll go there now and see what I can find out.

Alex

#6 06-12-2002, 11:43 AM

Dieselhead,

Was the compressor clutch engaged when you started putting in the first can? If it was NOT, then it was so low that the low pressure switch was not actuated. This switch interrupts the clutch in the even of low refrigerant to protect the compressor. Once you add enough to get the clutch to kick in, then the system is still undercharged so it begins to "short cycle." If this is the case, adding more refrigerant will charge it enough to get it past the point of short cycling.

Are you using guages? What is the low and high side pressure when this is happening. If you are not using guages, I highly recommend that you beg, borrow or buy a set. You are flying blind without them. You know what happens to pilots that fly blind, they crash into something.

Good luck,

DieselHead · #7 06-12-2002, 04:33 PM

Yikes! That crashing imagery was a little too much. I don't have any guages and unfortunetely, I don't know anyone who does who would let me borrow them. My goal when I started doing this was just to get the air blowing cold enough. I figured I wouldn't fill it to capacity and just add enough to make what was there just a bit better. Now, knowing that I don't have any gauges, do you think I should throw in the third can? Remember, two have already gone in. Thanks a lot!

Alex

#8 06-12-2002, 04:25 PM

Again, was the clutch turning with the engine running before you started? If it was not, you are probably just a little low on freon. I still would feel much more comfortable if you could borrow some guages. But, it is important to know if it was so low that the clutch was not engaged when you started.

Good luck,

engatwork · #9 06-12-2002, 04:42 PM

What's the effect of a "crash" versus blowing up an a/c system?
I'd let an a/c shop finish filling it if I did not have gauges.

#10 06-12-2002, 04:46 PM

Isn't it possible its over filled now? There is too much pressure, the sensor knows it and is cyciling the compressor?

#11 06-12-2002, 07:47 PM

Yes, without guages, it is tough. The only reason it is cycling now is that the high pressure switch is actually working now, the high pressure switch also cuts off the compressor when the pressure gets too high. Also, r134a systems have a high pressure blow off valve on the rear of the compressor, they all have one someplace on r134a systems.

Were you able to find the sight glass?? That is what the eye on top of the accumulator is called (Metal can I described before). If you look in there it will tell you whether or not the freon is low (Bubbles floating by either while the compressor is running or when it disengages)

I'm assuming those are 16oz cans of r134a, so they would be 1lb of r134a each, two cans should be close, do you have to put the entire 3rd can in?? Or can you just use some of it?? There is a sticker under the hood someplace that says how much freon goes in the ac, you may be just a bit undercharged yet. Its highly unlikely that you'd 'blow' up the ac system, that high pressure blow off valve is there to protect against that, old R12 systems did not have that kind of device installed. The blow-off valve resets after the pressure drops below a threshold. Around 325psi.

Or you can take it to a reputable place that can recover it and tell you how much they took out, the r134a machines do that.

Check the sight glass!

DieselHead · #12 06-12-2002, 08:39 PM

Larry,
Yes, I think the clutch was engaged before I tried this refilling experiment but I'm not entirely sure (I don't drive this car all that often).

I do think I'll give up though and let a shop do it. The $200 or whatever is worth the piece of mind and the assurance that if the shop messes up, they'll fix it.

Thanks everyone for the responses.

Alex

#13 06-13-2002, 10:05 AM

If there is no serious leak, I can't imagine this costing $200. If everything works, the shop can hook up guages, and properly charge the system in probably 15 minutes.

If there is a problem of some sort, that's an unknown cost.

If indeed the compressor clutch was engaged when you started, then I would certainly not add the third can. Don't you know ANYONE with a set of guages?

Good luck,

DieselHead · #14 06-13-2002, 11:50 PM

Larry,
Very unfortunetely, I don't. Most of my friends consider changing the oil a pretty complex operation. It's good to hear though that it might cost less than $200 because I had thought that that amount would be perfectly reasonable. I'm taking it in next week and I'll post what happened. Thanks

Alex

The Warden · #15 06-14-2002, 06:10 AM

Quote:

Originally posted by brandoncrone
that high pressure blow off valve is there to protect against that, old R12 systems did not have that kind of device installed.

Actually, my F-250 has a safety overpressure valve on the high side of the compressor. And thank goodness for that; otherwise I probably would have blown my compressor last week.

So, some R-12 systems have 'em