Both low 80's.

 

With more research I'm more convinced it is a bad pump. Now the question is, did I get it that way, or was there crap in my system that ruined it.

Will pull it apart when I get a chance and post what I find.

Thanks again.

 

with you stating your jumping the low side pressure switch im going to say you probably did it... running a compressor on low freon can be just as bad as running it without an oil charge.. that said at the same time there could have still been some stuff still in the system... if it was running before you changed the compressor you shouldnt have to jump the pressure switch... if it wasnt and you still had full pressure then id seriously suspect that pressure switch (this is part of the reason i always check the pressure levels before tearing a system apart to work on it)... i know you said earlier you were changing it because you found the system leaking at the pump... if you really had 80 psi on the low side with the engine off and the compressor not turning and still didnt kick on once you started it up and selected a/c then id be looking at that switch... regardless of the outside temp, 80 psi on a idle system is enough to kick the compressor on... now once it bleeds the pressure down itll kick in and out (depending on how low the system drops) till you get the system correctly filled...

 

Early on I swapped the pressure switch with a known good switch from another 150, so the switch wasn't the problem. From the get-go the problem was the pump wouldn't draw 134 IN to the system--unlike any other a/c system I've worked on.

It may have been contamination but it would have had to kill the pump essentially immediately. Old oil was very clean and orifice tube looked good, also.

Time will tell--I hope!

 

If you mean "pull apart" the compressor you'll void the warranty.

 

Okay, I'm doing my best to understand the situation:

1) You installed an AC compressor kit on your own, without flushing the system.
2) You used a pump and manifold gauge set to vacuum the system.
3) You then used off the shelf cans of R134a to charge the system.

Is this right?

1) You should always flush the system when installing a new compressor. Even if the old oil and orifice tube "look clean" doesn't mean they are - it's quite common for metal shavings to be present in old oil (much like you would see when changing transmission fluid). If you're going to warranty the compressor do not tell them you didn't flush the evap and condenser - they won't honor the warranty.

2) How long did you vacuum the system?

3) The problem with using small cans of R134a to charge an empty system is that they don't hold enough pressure to force liquid into the lines. That's why they are always set up to charge through the low side - because they depend on the compressor to be running and suction to be occurring to siphon refrigerant from the can into the system (that, and so nobody can get their face frozen off if they screw up trying to charge through the high side). Even if the whole system is in a "true" vacuum, you still need enough pressure to charge the system.

Jumping the low side switch simply proves there isn't enough charge in the system to allow the compressor to run. It's one thing to jump the switch momentarily to test the circuit, but to jump the switch and force the compressor to run and read pressures means you've likely damaged it. The whole point of having a low side pressure switch is to protect the compressor, because the oil that lubricates the compressor is also circulated by the refrigerant.

As to pressures -

In a sufficiently charged system, static pressure will reflect the ambient temperature - if it's 80 degrees, static pressure should be at about 80 psi (think of this more in terms of engine bay temperature).

If the system is working properly, high side pressure should vary from 250 - 350 and low side pressure should vary from 25 - 45. (These are very general numbers - it largely depends on ambient temperature and humidity levels).

If there is a low side restriction that blocks enough flow, the high side will build pressure up to a certain point while the low side pressure will continue to drop until the low pressure switch cuts off the compressor. It's a simple matter of input vs. output - a restriction on the low side that cuts off flow takes away the gas needed by the compressor to continue to build pressure. To look at it another way - if you completely plug the intake port on an air compressor, it won't be able to pull in air to fill and pressurize the tank - same concept with an AC compressor.

If there is a high side restriction that blocks enough flow, pressure will build until the high side pressure switch cuts off the compressor.

A momentary rise on the high side and no drop on the low side means you either have a bad compressor or there is a restriction in the low side preventing flow. You should try and get the compressor replaced under warranty and make sure to flush the system.

 

I appreciate your detailed response--though I disagree on a couple of points.

It's my understanding that many/most(?) manufacturers today recommend AGAINST flushing UNLESS the compressor has fragged itself or there are known contaminants. Ford is one of the few that think otherwise. Who's right? I've no idea.

The system was vacuumed several times, sometimes for hours.

It's very common to jumper the low side switch, and shouldn't cause any damage if done with a little care. In fact various ROMs say it may be necessary, to do exactly what you pointed out--draw refrigerant into the system. That's what I attempted and WHAT NEVER HAPPENED.

Your last sentence is exactly what I'm trying to figure out, and do. Thanks again.

 

personally ive never flushed a system.. if a compressor fragged itself everything was replaced including the hoses.. so i really have no opinion on the flushes..

my question here is in the second half of the line here... is that how long you left the vacuum pump running or how long you left the system vacuumed before filling?

i can tell you from working in dealerships and other automotive small shops this was something we NEVER did to fill a system... matter of fact its the first time ive ever heard it being mentioned as being a "common practice to do"... the vacuum is what draws the initial charge into the system until the minimum pressure is met... only time the switches were ever jumped was to test for bad switch on a known correctly filled system...

 

I can't speak to specific automotive manufacturers, but usually a flush isn't recommended if the system utilizes a thermal expansion valve, for 2 primary reasons:

1) Any debris could plug up or damage a TXV (this doesn't mean that it WILL happen, just that it could).
2) To flush a condenser on a TXV system would also mean flushing the receiver/dryer which will ruin the dessicant used to remove moisture from the refrigerant.

But even with these reasons, a flush can still be done if the TXV and dessicant are removed. When it comes to auto manufacturers, they always like to err on the side of caution.

That said, most manufacturers of aftermarket compressors will not honor the warranty if they find that the reason the compressor failed is because the system wasn't flushed, regardless of the auto manufacturer's recommendations.

As to jumping the low side switch - like I said, a momentary jump to test the circuit is fine, but forcing the compressor to run with a low refrigerant charge is not. Without a sufficient charge in the system, there simply isn't going to be enough oil circulating to properly lubricate the compressor. Think of it this way - if you drain the engine oil out of the pan until it's just level with the sump, is the oil pump going to draw oil in once the engine starts? Maybe - but it's probably not going to draw enough oil to keep the engine properly lubricated, is it?

I highly recommend you stop forcing the compressor to run - it can and will damage the compressor, even if it hasn't so far. I'm not an internet linguist so I don't know what ROM means, but any tech that genuinely understands how an automotive AC system works knows that forcing the compressor to run on a low refrigerant charge is a bad idea.

 

These systems have orifice tubes, not expansion valves--but it also would need removed to flush.

If Mercedes tell me not to flush, and 4 Seasons says to flush, I'd put my money on Mercedes' advice, warranty or no from 4 Seasons.

ROM = repair operations manual.