Another AC Problem - Page 2 - PeachParts Mercedes-Benz Forum

James L · #16 06-07-2010, 11:41 AM

dagobx

W124 expansion valves are located under the wiper, up next to firewall in engine bay, left of fuse box. Remove wiper assmebly and drainage grilles. No dash removal needed. While there, remove blower and clean area of debri, same on condenser up front. Debri can affect flow.

I have R12 manifold gauges, R12 recycle machine, vacuum pump, leak detector and other a/c tools. I live in Greenville, NC. (2 hours from Manteo) (1 1/5 hours from ocracoke ferry). I love Hatteras Island; Rodanthe, Avon, Salvo, Avon, Buxton, Frisco and understand the area and your plight! You live near the the Beach? hehehe!

bobodaclown · #17 06-07-2010, 01:34 PM

I changed out the fans on my 92 W124.128 While your working on it you may want to wash out the bugs from the front grill. There is about 2 inches of cover on the bottom of the fan mounts. It loves to catch bugs. That's about 2 inches of no airflow due to dead bug carcasses and such.

James L · #18 06-07-2010, 02:56 PM

Agreed, on my cars I went so far as to purchase non-acid-bio-degradable evap cleaner and coil cleaner from the local hvac supply. Good for home units also. Agree that bugs and grime can cut air flow to coils. This raises pressures and can cut cooling performance.

dagobx, go for a 45 mph + test drive, turn a/c on with blower on lowest setting. Observe vent temp with thermometer with this low blower setting and fast non-stop highway speed. This will give the evaporator coils time to cool down and see if it can reach a 40-45 degree vent temp.

Quirky Mercy · #19 06-07-2010, 11:35 PM

If you pack a vacuumed recovery cylinder in dyr ice you can use it to recover most of your R12. There is a replacement refrigerant for R12 that Napa sells for 8 bucks for a 12oz. can. I think Your rig needs 2.4 lbs. It states it will mix with 12 or 134a. Or you could use Hotshot. You really need those pressures as they will tell alot. Is the suction line cold to the touch or just cool? Are You shure You got all the old oil out? 60 deg. is warm air up here!

jcyuhn · #20 06-08-2010, 10:19 AM

Quote:

Originally Posted by Dirtypants

Behind the dash is the heater box. It has a heater core and an evaporator and several doors that direct air flow. Heat comes from the heater core(duh) and cold comes from the evap. Depending on the temp you dial in and the temp reading from the interior temp sensor, the door moves to direct into the cabin from one or the other or both. If the door doesn't close all the way on the heat side then instead of full cold a/c your getting full cold plus a little heat.

That's not how it works on the 124. The air always passes over both the evap and the heater core. The temperature of the heater core is regulated by the monovalve, which pulses to admit hot coolant into the heater core, and hence regulate the temperature of the output air. Of course, this time of year the monovalve is expected to stay closed all the time, no heat needed.

Air direction on the 124 is pretty simple. The outside vents are always on, hot or cold. The center vents open if the car needs cooling, whether in AC or EC mode. The floor vents open if the car needs heating, again whether the ACC is in AC or EC mode.

dannym · #21 06-08-2010, 11:35 AM

Quote:

Originally Posted by jcyuhn

That's not how it works on the 124. The air always passes over both the evap and the heater core. The temperature of the heater core is regulated by the monovalve, which pulses to admit hot coolant into the heater core, and hence regulate the temperature of the output air.

So, pinching off the supply hose from the monovalve would be a better idea than pulling the dash apart.

I would like to know how much and what brand of refrigerant oil he put in.
As well as the pressures of course.

Did you flush everything? Evaporator, condenser, hoses?
How did you do it without removing the expansion valve?

Danny

dagObx · #22 06-08-2010, 04:14 PM

OK, guys, here's what was done when I had to replace all the stuff:
-New condensor, dryer; did not replace compressor or expansion valve.
-Tech did the flushing - I can only assume he did it right (whatever that is). Also put in new mineral oil while system was apart.
-Tech installed new condensor, dryer, I pulled vacuum on system for 24 hrs. - no leaks detected.
-Charged system w/R-22 (small charge) to check for leaks w/leak detector, found none.
-Vented R-22 into friend's canister (had a vacuum on it), charged system w/R-12. Pressures at the time were all over the place - Hi= 170-something, Lo= 80 or 90-something. Gauges were crap, so couldn't really tell. Put in about 3 12oz cans R-12.

Now, this car has never really had good cooling. Even before the crash w/R134a it never cooled more that 60* at the vents - that was after taking it to a different shop to have the AC checked by a guy that's supposed to know what he's doing with R-134a.

So, with no apparent leaks & a compressor that seems to be doing it's job, I figured the next best thing to do is replace the expansion valve per my HVAC friend's suggestion. I will lose all my R-12, but I just found a leaking Schrader valve that has let out most of the R-12 anyway. This valve has only JUST started leaking, after checking pressures again, so it's not why the thing wasn't cooling to start with.

Expansion valve is on order, should be here tomorrow. I'll get that done, recharge & report back.

BTW, James L: My tech says the expansion valve on my '87 W124 is under the dash. You sure about it being on the firewall in the engine compartment?

Quirky Mercy · #23 06-08-2010, 08:05 PM

I would not put R22 in the system ever! If you need pressure use compressed nitrogen. then vacuum it again. If you had no leaks with a vacuum on it just put in the refrigerant. What is the recommend amount of refrigerant for Your car? Your low side reading seems high if it were correct.

jcyuhn · #24 06-09-2010, 11:10 AM

You need good guage readings for a solid diagnosis. But from what you've posted, your high side is low and low side is high. Either the expansion valve is stuck open or the compressor is faulty. If the compressor does not make any untoward noises, I would suggest replacing the expansion valve and then see where you are at.

The 124 expansion valve can be replaced without removing or disassembling any other components. I've done it a couple of times.

dagObx · #25 06-09-2010, 01:11 PM

Quote:

Originally Posted by jcyuhn

You need good guage readings for a solid diagnosis. But from what you've posted, your high side is low and low side is high. Either the expansion valve is stuck open or the compressor is faulty. If the compressor does not make any untoward noises, I would suggest replacing the expansion valve and then see where you are at.

The 124 expansion valve can be replaced without removing or disassembling any other components. I've done it a couple of times.

This is what I've been thinking. Compressor runs fine, no noises or hiccups. Expansion valve is due today from UPS, so we'll see what happens when I get it installed.

Quirky Mercy - we only shot a very small amount of R-22 into the system to check for leaks. I read somewhere that R-22 could be used in small amounts to do this. Didn't have access to nitrogen & don't want to waste the R-12, since I'll have to open the system to install the new expansion valve.

LB - no, this is not a Euro, so I guess I'll chech under the hood for the expansion valve. Hope it is there, it'll make changing it over a LOT easier.

Again, will report back when the expansion valve is in & system re-pressurized. I think (hope) that will solve my problems

.

dagObx · #26 07-04-2010, 12:45 PM

Well, I finally got my new TXV valve & got it installed last week. Refilled the system with R-12. Final pressure readings (thanks to my 'new' old gauge set) were 160 Hi, 35 Low. Ambient temp was 80 degrees F. R-12 was very slow going into system, but the hot water bath improved on that by a factor of 20.

Unbelievable how much difference there is from how the system operates compared to what it was doing with 134a. Lowest temps with 134a from the vents were around 60* regardless of ambient. Now it easily drops the vent temps to around 45*, which is plenty cool for me. The aux. fan actually work now! Ambient temps out here have been in the low 80s lately, so the real test will be next week when temps are forecast to be in the upper 80s to low 90s.

Anyway, I could not understand why changing the TXV valve could make such a difference. The old valve didn't look dirty or damaged. It could be that it was changed out by the previous owner when converted to 134a, but there were no labels on the old valve.

Long story short, I now have decent AC! For those that want to convert to 134a - DON'T!! Keep your system R-12 as it was designed for...

Sorry for the long post, but I am excited to have cooling!

leathermang · #27 07-04-2010, 01:48 PM

That is not a long post...
that is a true and good post...

#28 07-04-2010, 10:12 PM

Quote:

Originally Posted by dagObx

See Another AC Problem for background.

Well, I finally got my new TXV valve & got it installed last week. Refilled the system with R-12. Final pressure readings (thanks to my 'new' old gauge set) were 160 Hi, 35 Low. Ambient temp was 80 degrees F. R-12 was very slow going into system, but the hot water bath improved on that by a factor of 20.

Unbelievable how much difference there is from how the system operates compared to what it was doing with 134a. Lowest temps with 134a from the vents were around 60* regardless of ambient. Now it easily drops the vent temps to around 45*, which is plenty cool for me. The aux. fan actually work now! Ambient temps out here have been in the low 80s lately, so the real test will be next week when temps are forecast to be in the upper 80s to low 90s.

Anyway, I could not understand why changing the TXV valve could make such a difference. The old valve didn't look dirty or damaged. It could be that it was changed out by the previous owner when converted to 134a, but there were no labels on the old valve.

Long story short, I now have decent AC! For those that want to convert to 134a - DON'T!! Keep your system R-12 as it was designed for...

Sorry for the long post, but I am excited to have cooling!

Good show!

vstech · #29 07-04-2010, 10:47 PM

165n sounds low even for 80 ambient, methinks you'll be adding more 12 in when it gets hot. very good show!

dantheman67 · #30 07-05-2010, 02:36 AM

That's Excellent. I got my new R/D and TXV in the mail a couple days ago and obtained some R12 too. Looking forward to when I have time to rebuild the A/C system.