Replaced just about everything Ac won't work

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gregpurcell

gregpurcell

Greg Purcell
Joined
Aug 21, 2008
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Location
Near Savannah, GA
Wow, I'm frustrated!
I have a 72 Scamp with a slant. It's an ugly 4 door driver, but it HAS to have working ac. When I got it, some of the factory ac parts were missing and some were replaced with aftermarket and hose clamps, etc..it was a mess.

I chased down all the correct hoses to and from the compressor, got a good used factory condensor, put in a new dryer and put it all back together. I upgraded to the new green O rings. I even replaced the dash vacuum switch because I wasn't getting power to the compressor (even with the pressure switch shorted out of the circuit). (The dash switch fixed the problem with power to the compressor)

This is the second time I've charged it with the same result. I pull a vacuum for an hour, let it sit and there's no leaks. I charge it with an R-12 drop in. (NOTE: At this point I don't have the patience for a lengthy discussion on the perils of flammable hydrocarbons vs 134, etc. The problem I'm having would most likely come with any refrigerant) I seriously doubt it's a charging or overcharging problem.

After 1 can, the compressor kicks on and sound's good (no knocks or rattling). The high pressure goes away almost to zero, and the low side stays between 25-50.(Before anyone asks, I DO have the hose hooked up correctly, gas comes out if you disconnect it from the gauge set. I've had people say "it CAN'T be on zero"..it is. It goes up slightly if you turn the compressor off.)

It acts like a restriction in the line.

I thought it was the expansion valve. I just put a new one in. I pulled all the hoses and individually each checked for blockages. You can blow through all of them. The same is true of the condensor. I put it back together, charged it and it was the same.


The only thing I have found is that the evaporator in the heater box seems to be a little restrictive (as determined by blowing air through the holes with all the hoses (and evaporator valve) disconnected. You can blow through it but it requires some effort. I have two heater/ac boxes from parts cars here and they seem to flow better than the one in the car.

This is one of those situations where if you change enough parts, it will all be new and will pretty much have to work!

I'm down to two options (there's only two original AC parts left on the car!) #1. Replace the heater box and evaporator. It's a pain and I'd rather not if I don't have to. Is the reduced flow there a potential cause of my problem?

#2. I could replace the compressor. The one I have runs well and doesn't make noise. I was always told that's how you determine if it's good. Is it possible that the reed valve or something internal could keep it from making pressure? (Again, respecfully, I'm not interested in discussions about converting to newer parts, etc. I can get the compressor it came with new and bolt it on in a hour. I'd do it in a minute if I thought it would fix the problem. It would SUCK to replace it and still have what I've got now!

I would really appreciate any constructive suggestions from anyone who may have had a similiar problem!

Thanks in advance!
 
This would be typical of a bad expansion valve except the low side should go low

You have enough R-12? The shop manual shows 2 lbs 14 oz "with a 2 row condenser"

Oh and.........do you have a shop manual?

Free download:

(Thanks to AbodyJoe)

[ame]http://www.abodyjoe.com/pictures/Misc.%20car%20info/1972%20Plymouth%20Chassis%20Serv%20Man.pdf[/ame]

Does your compressor have service valves, and could one of 'em be shut?

Are you absolutely sure that both service valves are getting depressed, or otherwise not plugged to the gauge manifold?

Is this the factory compressor? Maybe the EPR in the compressor is stuck?
 
Expansion valve is brand new. No Service Valves. Factory compressor. I was looking at the EPR valve in the shop manual. If/when I replace the compressor (perhaps next) It should have a new one! :)
 
Since you're having troubles anyhow, you should be able to get some idea of the condition of the compressor as an air pump. "Rig" a temporary plug for the outlet, leave the suction service port open to air, and see if it will pump pressure. If you get ambitious, you can do the same on the suction side to see if it'll pump down.

"Ferd," for all the flak they take on this site, at least had "real" service valves, as did my old aftermarket system--a real advantage when trouble shooting.

"New" does not mean functional, either. Specially nowadays
 
What is the static pressure when the system is off, both valves shut on the gauges(not the shut off valves on the hoses but the ones right at the gauges)? Does the low side pressure drop when the system goes on?
It seems as though your pressure on the low side is too high & obviously the High is way too low. At 1st glance it looks like a bad compressor. Assuming the readings are when it's runnning(copressor clutch engaged) & (I know, I know) the gauges are hooked up correctly.

A properly charged R-12 system pressure rule of thumb is:
Low(suction) reading should be about what your evaporator core temperature should be. (Approx26-34 psi.) This is CORE TEMP not the air temp at the registers.

High(discharge) side reading should be roughly 2X the ambient air temperature or 3x the humidity percentage of the ambient air. I.E. 75* ambient air temp should have a discharge pressure of about 150psi. If it is a very humid day you could expect to see the pressures higher. I.E 75* day w/ 85% humidity might give a reading of 250 psi.
A/C pressure readings are never exact, but they should be in the ball park.
If you had a blockage in the low side, which is from the expansion valve back to the compressor (which would include the evaporator core), you would have a low pressure or even a vacuum reading with a good compressor & a full charge. On the high side you'd have abnormally high reading if there is blockage anywhere(as long as it's not between the compressor & hi side svc. valve ) on the discharge or suction sides. If the reading you have are w/ compressor clutch engaged I'd have to say the compressor isn't pumping or pulling.
 
If you have a restriction in the evap. core the low side would have the pressure drop. Have you put the correct full charge in it and tried it? Sometimes the depressor in the end of your hose doesn't press down on the shraeder core in the service port enough to read correcly. What does it read on your high side gauge with the system off? Both sides should be equal without the compressor running. If it has a restriction it would be between the compressor [rv2?] and the high side port, in the condenser, to cause a drop in the high side.
 
I re-read your post again & just to clarify, you will get refrigerant to blow out of both sides of the system when either the hose or service valve is opened up. So if that is how you are confirming they're hooked up corectly, hi vs low, you better check again because they could be backwards!
 
65cuda360 said:
If it has a restriction it would be between the compressor [rv2?] and the high side port, in the condenser, to cause a drop in the high side.
Click to expand...

Not true. If the TXV is plugged, you will still see a drop in the high side although there should be some pressure there. This is because the refrigerant is doing no work, and is simply condensing and subcooling in the condenser core.

Or to be clear, maybe you and I are using unclear terms. A restriction will NOT cause ABOVE normal high side pressure unless it was something like foreign material between the compressor and condenser.
 
I went outside this morning and the sun was shining right on the hood of the car, so it was perfect lighting for pictures and I got a great idea!

You guys are all better than I at this, so here's some pics of the gauge setup, and closeups of the gauges both static and with the compressor running. Hell, sometimes I don't even know which scale to use, so here's the actual numbers. Assume an ambient temp of 70 degrees and a one (8oz) can charge of Duracool r-12 replacement, which is supposed to be installed to 40 percent of factory r-12 specs.

I assume that the charge is low because when I saw that the high side was doing what it did before (with a higher charge) I decided not to waste another can of refrigerant.

ac1.jpg


This is static shot.engine off and single gauge closeups

ac2.jpg


ac3.jpg

ac4.jpg


Engine running compressor engaged

ac5.jpg


ac6.jpg

ac7.jpg



Well, a picture is worth a thousand words, so hopefully this helps!

I appreciate all of the ideas so far! What you have all confirmed so far, is that I probably have one of two problems: Either there is a restriction in the evaporator or the compressor is not pumping. (assuming of course that I didn't get a bad expansion valve or hook it up wrong)
Since those are the only two remaining original parts of the system and I'm taking this as a "change the parts until it works" attitude, I'm probably going to replace them one at a time. I'll start with the easier of the two, the compressor! IF it still doesn't work, I have extra heater boxes and I'll bite the bullet and swap it too.
Thanks for all the help!
 
I think we're saying the same thing......if his pressure readings are accurate, the compressor functioning, and the charge correct, the pressure would drop from the restriction back(thru the low side) to the compressor.With the pressure drop on the high side, the restriction would be somewhere from the access port in the liquid line back to the compressor. The compressor would fill the condenser with liquid behind the blockage (subcool).
 
At this point the only possible line restrictions would be the slight restriction in the evaporator (which I know about) or a bad or improperly installed new expansion valve. I have edited the above post to include pics of the gauge pressures.
 
Your post came in while I was typing. Looks like gauges backwards and charge low.
 
High side is between compressor and cond. coil, up by radiator.Low side is from compressor to evap. coil, in heater housing behind firewall.
 
First pic is of gauge hookup: one fitting on the head of compressor-I have that as high. Other fitting on discharge hose to condensor.I have that as low. Is this backward?
 
It sure appears from the picture that you hsave the hoses on backwards? High side goes to the front of the car, low side to the rear. This is how I was taught to remember it.
 
IT'S COLD IN THERE!

I put three 8 oz cans cans charge. It's 75 here now and it's cold. Will it be cold at 100 degrees? I don't know.
Here's the final gauge readings engine at idle, ac on. I appreciate the help A LOT! Any ideas on those readings still appreciated. With AC, I'm like a 3 year old with a loaded revolver. I know just enough to pull the trigger!
BTW..stupid question: Really! Which gauge scale are you supposed to use?

<blush>

finalac.jpg

finalac1.jpg
 
Those gauges aren't helpin' any as they don't have R-12 temp scales, so you'll have to read pressure and convert to temp.

(In other words, read the pressure scale, and refer to the chart I posted below)

You want to read through the manual and duplicate as much as possible the test conditions they use. Depending on how much air you have over the condenser, high side press/ temp can be as much as 30* higher than ambient. I ALWAYS check what is known as COMPRESSOR SUPERHEAT which is a measure of protection of how much or how little liquid is being returned to the compressor. Get a probe type thermometer of some type, tape it at about the 8 o'clock position under the suction metal tube before it goes into the compressor, and wrap something around for insulation. Even a couple of rags are better than nothing. You want the converted pressure / temp on your gauge to be above the thermometer reading by at least 20*F If the difference is down around 10F or LESS you are getting too much back toward the compressor and in danger of "slugging" the compressor with liquid. Measure this with the pass. compartment cooled down

Once again, you need some method of GETTING AIR across the car radiator so that you can duplicate "running" conditions.

Here's a chart:

3992604130_60c40f2a32_o.jpg
 
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