ARRGGGH! Another Compressor won't engage post! - PeachParts Mercedes-Benz Forum

pdrayton · #1 07-23-2008, 10:37 PM

Yep, another compressor won't engage post.

New parallel flow condensor (original condenser sprang a leak). More oil (150 ml - 50 for each of the condenser, drier, lines).

Vacuumed to 26 mmHG for 2 hours, and recharged with equivalent of 3 lb R12 with Envirosafe R12. Low and hi side are 75 PSI. But the compressor won't engage.

I shorted the pressure and temperature switch and the aux fan and compressor wouldn't switch on. Fuse 8 (compressor) is good.

What the hell is going on? Why won't the aux fan switch on? Geez, I thought I knew what was going on with the AC on the W123.

Pissed off.

jkoebel · #2 07-23-2008, 10:40 PM

Is this the 240D? Check the relays under the black cover on the left fender in the engine bay. Both of those are involved in the operation of the A/C compressor clutch.

pdrayton · #3 07-23-2008, 10:48 PM

Yep 240Dt like yours, same year.

Thanks for the reply.

but why would the relay be blown when everything was working fine before the condenser blew? The compressor would engage before the replacement.

Anyway, how do I check the relays?

Matt L · #4 07-23-2008, 11:12 PM

I hope you don't really mean 26 mmHg as that is very little vacuum. 26 inHg is more believable, but still not good enough to boil off the water in the system. Of course, that isn't your problem with the compressor not starting. It will just shorten the life of the parts once you do get it going, regardless of what EnviroSafe tries to tell you.

jkoebel · #5 07-24-2008, 12:05 AM

The relay would be blown potentially because it sat not moving for a while, and seized up randomly?

Jump the compressor clutch. The wire with the brown stripe is -, the other is +. (although reversing will not hurt it if you just do it for a second) directly to the battery with a switch. When the switch is engaged or you hold the terminals together at least, the clutch should click into place. It could potentially have failed.

If the A/C cools with the clutch jumped, then it's something further up the chain. If you're sure the evap. temp, pressure and temperature switches are good, as is the "compressor wanted" switch in the cabin, then it's a relay.

jkoebel · #6 07-24-2008, 12:12 AM

Search for the W123 240D A/C FSM, one of the pages selling it has a copy of the circuit wiring diagram. I own a paper copy but no scanner.

pdrayton · #7 07-24-2008, 07:17 AM

Matt, yes, I meant 26inHG. I thought the standard vacuum was 27inHG for an hour? So considering it is about 90F here, I thought that would compensate....

JKoebel - Thanks, I have the FSM, I 'll have a look. And jump the compressor

Whiskeydan · #8 07-24-2008, 08:05 AM

How'd you get 3lbs in there without the compressor running?

vstech · #9 07-24-2008, 08:30 AM

if your gauges are accurate, then 26inHg is showing you have a leak... in 1 hour you should be pegging the 29inHg mark on your gauges.
best way to check is with a micron gauge, but they are not easily attainable...

and it is simple to put in 3Lbs with no compressor engagement, you put in liquid in the high pressure hose... done.

pdrayton · #10 07-24-2008, 09:51 AM

I was using a fridge compressor to evacuate it - they only go to about 26 inHG. And it stayed there, so there is no leak, or at least a leak is not the problem.

The pressure is still there this morning but it's dropped a little, I guess because of the drop in temperature in the morning. Pressure is now 70PSI -that's enough to switch on the compressor isn't it?

I just realized I may have put a little too much ES-12 in - I put in just under 3 of the 6 oz cans, which they say is the equivalent of about 18oz a can. So that's 3lb 6oz and the 240D is only supposed to have 2lb 9 oz right? So that's quite a bit over.

However, that wouldn't stop the compressor switching on, especially since I had it switched on after the first can and it never came on. Time to jump the clutch...

Whiskeydan · #11 07-24-2008, 10:51 AM

Quote:

Originally Posted by vstech

if your gauges are accurate, then 26inHg is showing you have a leak... in 1 hour you should be pegging the 29inHg mark on your gauges.
best way to check is with a micron gauge, but they are not easily attainable...

and it is simple to put in 3Lbs with no compressor engagement, you put in liquid in the high pressure hose... done.

Tell me how it remains liquid in the "evacuated" system??? I say it is NOT possible to put 3lbs in without condensing. If the OP has reads 75psi on both lines, the last 'empty' can had to have 75lbs psi when disconnected.

I'd suggest jumping the compressor clutch to +12 volts and see what your pressures do. If the low side goes into a vacuum add more. It could be the low side switch needs to be 'tickled' into action. Seen it before...

Matt L · #12 07-24-2008, 10:53 AM

I don't recall the table, but I don't think 26 inHg is enough to boil the water out. If you do it again, you may get a bit better vacuum with the fridge compressor if you add a bit of DEC PAG 46 to the inlet before you start. I still purchased a dedicated pump, even though I have access to free fridge compressors.

Did you check for voltage at the clutch? It could be that your compressor is harder to start now, and the clutch gap is too wide. ESPECIALLY if you charged a liquid into the low side. If you did, don't force it to run. Turn it by hand a bunch of times. So many times that you think your fingers are going to come off.

Matt L · #13 07-24-2008, 10:54 AM

Quote:

Originally Posted by Whiskeydan

Tell me how it remains liquid in the "evacuated" system??? I say it is NOT possible to put 3lbs in without condensing. If the OP has reads 75psi on both lines, the last 'empty' can had to have 75lbs psi when disconnected.

I'd suggest jumping the compressor clutch to +12 volts and see what your pressures do. If the low side goes into a vacuum add more. It could be the low side switch needs to be 'tickled' into action. Seen it before...

It is very possible (and industry standard practice) to charge as a liquid. It must absorb heat to vaporize, and this heat will be easily given up when it condenses.

When you charge as a gas, you are absorbing heat in your can and that heat must be released into the system, thus it takes a long time, or a compressor.

Charging as a liquid does not need any help from the compressor at all. It's possible. I just did it. Most professionals do it every day.

Whiskeydan · #14 07-24-2008, 11:02 AM

I understand charging with liquid. I do it as well to speed the process.

However, I still say it is not possible to get a full charge, from cans, in the MB AC system without the comp running.

vstech · #15 07-24-2008, 11:03 AM

this is why it's important to weigh in a charge.
if you don't think you can put much freon in as a liquid, try it.
I have seen 10Lbs get dumped into a car system... the reciever frosted over, and the over pressure switch prevented the system from running when the guy tried to check the pressures.

a 30 Lb bottle makes it very easy to overcharge a system on the liquid side.