'94 RMW -- A/C question and random noise...

Hi all -- a couple of questions:

First -- had the compressor replaced last fall, and it never got hot again after doing so. This spring, noticed it was cool, but not cold. Had the pressures tweaked a couple of times as it started getting warmer outside, and they had to keep cleaning out some orifice, which helped a little.

However, I wasn't getting much airflow. Ended up that mice had built a nest in the evaporator. They cleaned that out.

Now apparently the freon levels are topped off, and I have plenty of airflow. But since it's been like 100 degrees, the air is still only cool, not cold. What would be the next thing to check for? Evaporator? Condenser? I don't think it's leaking freon, or that I have a bad compressor, as it is cooling, and the problem isn't getting any worse.

Second issue: Sometimes when starting the car, if I have the door open when I do so, I hear an electrical shorting sound right after it starts. I think it may have something to do w/the delay before the blower motor kicks on.

I've only heard it when I've had the door open, but it's pretty loud. Anyone ever encountered that before?

Can't help with the 'shorting sound', but when it's as hot as it has been, the only way to see if the AC is up to snuff is to get the car on the freeway for a steady 15 minutes or so and see if you finally get a nice blast of cold air on the 'recirculate' position while driving.

Under the dash the heat and AC are "always on". What I mean is that the heated water always goes through the heater core and the temp is adjusted by a "blend door" in the duct work. Block off the heat and you are left with cold.... leave the door open a little and you have cool (or warm) air. That door is what adjusts the temp.

@Jim: After being on the highway for a while, it does finally get somewhat comfortable, but it never gets as cold as any of my other vehicles.

@Krz: So basically, if I understand you correctly: If something were wrong w/the evaporator, condenser, compressor, etc. -- it wouldn't be as cool as it is and makes the blend door issue more likely?

Thanks, guys, for the info.

If they had to keep cleaning junk off of the orifice tube that means your system is contaminated
with some form of trash.Do you know if they thoroughly flushed the sytem before installing the
new compressor?The other thing is did they draw the system down using a vacuum pump usually
for 20 to 30 minutes prior to charging.Dont know who did the compressor install but it may still
be under warranty.
My 2 Cents

My '96 had an issue with the blend door sometimes sticking or not closing fully. The "fix" was to run the temp up to full hot, and then lower it to full cold.. Sometimes I did that twice and it would finally start blowing ice-cubes at me. Worth a shot!

If you'd had the battery out, and did not turn off the climate control first, that can also cause the blend door to not go to the proper position. In most cases doing the trick above fixes it.

Also, does you car have the engine-driven fan that came with the tow package? If so, your fan clutch may be weak and not pulling enough air at lower speeds. With a weak fan clutch, you'll normally feel a change in temp when coming to a stop. You will also have an electric fan, is it running when the a/c is on full-cold?

Just brainstorming!

As for a clogged orifice, that is a sealed filter in the system, and the only reason it would be clogging is if your previous compressor shelled and they people that did the a/c work did not flush the system out well. Having a mice-nest in the evaporator would only block airflow, it would not change vent temps.

-Mike

-Mike

81X11 wrote:

My '96 had an issue with the blend door sometimes sticking or not closing fully. The "fix" was to run the temp up to full hot, and then lower it to full cold.. Sometimes I did that twice and it would finally start blowing ice-cubes at me. Worth a shot!

I ground down the end 'stop' on the temp control to gain a little more travel, just to insure that I could close the duct completely. Now I can hear the door 'thump' closed on both ends of the control.

By chance do you have the dynamic operating pressures for the system? What about static pressures? Provide ambient temperature when stating pressures.

All good responses so far. As mentioned, constant "cleaning" of the orifice tube indicates an improper flushing of the system prior to the new compressor being installed. Some condensers cannot be flushed due to design, replacement is the only fix. Also, with a system that old (18yrs) was the accumulator replaced too?

As far as "topping off" the system, how was this determined? Is there now too much refrigerant in the system, overcharged? This can be detrimental to proper operation. Are you using R134a or R12? '94 should have R134a. If I remember correctly, this was the cut-off year for R12.

Depending on ambient temperature, I typically shoot for 40 degrees below that for vent temperatures, some systems may get cooler. Blend door could be an issue here as mentioned by a few.

As mentioned, a system that has been open does require a 30-45 minute evacuation time, depending on how long it was open to the atmosphere. This procedure removes moisture from the system.

Make sure the fan clutch is operating correctly, not enough airflow past the condenser will cause the high side pressures to get too high and the system will not cool properly, as will an overcharged system. Make sure any shrouds that came from the factory are in place and not removed.

I typically troubleshoot A/C systems using the pressure readings and outlet temperatures, removes guesswork. Although, there is nothing like being right there troubleshooting the system as it is happening.

gmtech. Hmmm. Gee, seems to me I've seen that handle, but with a different (long necked) avatar?
(note to others: if it's the same fellow, he's quite knowledgeable in the field)

Anyway, I can confirm that the 94 has a parallel flow condenser, so it should have been replaced, not flushed. The accumulator should also have been replaced (usually voids the compressor warranty if it wasn't).

Bear in mind that the cooling capacity of the AC system is greatly affected by what is being cooled. The AC system doesn't lower air temperature directly, it squeezes a fixed amount of heat energy out of whatever is in contact with the evaporator. If that something has a low heat capacity, the temperature drops a lot more than if that something has a high heat capacity.

Dry air contains a lot less heat energy than humid air at the same temperature. If it's 100°F out but only 20% RH, the centre duct temperature might get as low as 57°F. But raise the RH to 60%, and the duct temp might be 78°F. At 100% RH, the duct temperature will be quite warm because the high side pressure will repeatedly exceed 429psi, causing the PCM to shut down the compressor each time.

As long as my old OCC continues to blow around 45 to 50 degrees at the outlets I am satisfied.
It was about 105 degrees with the heat index and the outlet temp managed to get down to 50
on the longer stretches so I am happy.Now the 04 Crown Vic stays around 40 degrees no matter
what the outside temp or humidity is.Its actually painful to get into the car when you are really
sweating alot but I can live with that!

The accumulator was changed -- the condenser was not.

I'm not sure what the duct temp is -- I'll have to stick a thermometer down in there to check...

It was over 100F today, with probably 40% humidity. I did the high/low temp switch, and it may have helped some, but not a lot. When I'm on the highway for a while, it gets better. But on side streets it starts falling behind.

It has R134a and does not have tow package, BTW...

Does this car have an electric fan?
If so, is it running?

Well, it will have at least one electric fan -- it's a 94. Does it have RPO code V03? The base cooling has a 150W primary fan on the right and a 100W secondary on the left. RPO V03 indicates the secondary fan was upgraded to 240W. (V08 is the HD cooling, with mechanical fan and 240W secondary, that came with the towpack)

At 100°F and 40% RH, the FSM says the system should be able to produce a 64°F centre right duct temperature at 2,000 rpm.

Lower RPM will produce higher duct temperatures because the compressor isn't at optimum speed. Poor airflow over the condenser will produce higher temperatures because the heat energy is not being removed from the system. To tell which is the greater effect, try misting the evaporator with a garden hose and sprayer nozzle (which will absorb more heat than dry air) If the centre right duct temperature drops significantly, then check the condenser closely for bent fins or debris between the condenser and radiator as well as fan operation.

If the compressor shed metal particles when it died last year, those particles went straight into the condenser. That condenser is a parallel-flow design, which means there are multiple paths from the inlet to the outlet. The design is more efficient, but impossible to flush completely and evenly. The orifice tube is in the line at the condenser outlet. As gmtech pointed out earlier, those particles can only come from one place: the condenser.

Running the AC with a partially plugged orifice tube screen can have a side-effect beyond inefficient cooling. The oil is carried through the system by the refrigerant. If you restrict the refrigerant flow, you restrict the oil flow, eventually starving the new compressor of oil. That is generally considered a Bad Thing. I would give serious consideration to having the condenser changed. Sooner rather than later.

I have no idea on what kind of fans it has...and I think my RPO sticker is gone. I guess I can pull from compnine...

I think that's what I'll end up doing...i.e. new condenser...

I can't keep driving it like this, and I don't want to risk damage to the compressor....

As gmtech said, you need to know what the dynamic pressures are to really know what is going on inside the system. Changing the condenser will protect your orifice, but we don't know that is the only problem.

I wrote a series of posts on the Roadmaster forum about the B-body AC systems as well as some diagnostic tips on what the pressures may mean. You may want to review it. The diagnostics start on the second page.

You SHOULD replace the condenser, but if your electric fan(s) aren't running, which is a real possibility, it would account for your lack of cooling. If the car spent it's life with the AC on a lot of the time, the fan motors are quite probably not working anymore. To check, all you have to do is look at them while the AC is on. They should be running.

The primary fan only comes on when the HS pressure exceeds 190psi and cuts off when the pressure drops to 140 psi. The secondary comes on when the HS pressure reaches 240psi. and cuts out at 210 psi.

To check if the fans are working just unplug the temp sensor on the water pump and start the car they both should turn on.

I'll be... i thought they came on with the AC.

It doesn't take much to hit 190psi on the high side. Pretty much any time the ambient air temperature is above 70°.

jimbeau wrote:

I'll be... i thought they came on with the AC.

The primary might but last summer when I did the switch from a mechanical and before I got it wired while idling it took a while before the secondary fan would turn on. I am pretty sure it took the water temp to reach the set point to turn on. I just know that disconnecting the WP temp sensor and starting it will cause both fans to come on.

The PCM will turn the fans on based on coolant temperature -- primary above 107°C (225°F) and secondary above 111°C (232°F) -- and AC high pressure -- primary above 189 psi, secondary above 240 psi. Plus it will turn the fans on as a fail-safe when certain faults are detected (like ECT sensor failure from unplugging the connector)

The PCM will turn each fan off again when the coolant temp drops -- primary below 103°C, secondary below 107°C and the AC pressure has dropped -- primary below 150psi, secondary below 210 psi, however the minimum run time for the primary is 50 seconds and the minimum run time for the secondary is 26 seconds.

The PCM will also shut down the fans when the vehicle speed exceeds a certain threshold. I have no idea what the exact number is, but I would guess it is related to the maximum air flow speed the fan can generate. Why run the fan when the air speed is already higher?

buickwagon has provided a good deal of information here.

I would like to provide a wiring diagram here of the electric cooling fan system to hopefully make troubleshooting the electrical aspect of it a slight bit easier.

Here is a graph of my turn on temps for my secondary fan from the original programing on my Roadie.



Here is what I have it set at now after the switch to the dual electric setup along with an electric WP and 160 thermostat.

The X-axis is MPH? Amazing. I had no idea the VSS was capable of such fine resolution. Or are those lines just a projection based on the two data points at 1mph and 2mph?

Getting condenser replaced next week... Too hot to limp along w/o it.

&$&@!@$!!

Condenser replaced... Not much improvement...

What else is there to fix? How cold should the air be at the vents?

Today it was low 90s instead of mid 100s -- and it was better. But shouldn't it still cool at 106-107?