MX-5.. Q on A/C compressor

[Ant]

I am posting here because this area is my "home".

Compressor is not kicking on!
Background:

-Recovered R 134a before engine removal in Jan.
-Had it recharged at end of May. At that time the Low & High side were both showing 50psi. I went into the shop to watch the readings as it was charged. A/C was still blowing cold air, so I took the car.
-Worked well until last week. Started car, flipped on a/c and clutch did not engage.

1. Tested clutch relay= ok
2. Tested the relay circuit (cavity)= ok
3. Tested continuity to to the clutch switch ground=ok.

Not getting power to the clutch switch when car is running and a/c knob is turned. Wiring is not pinched anywhere along the route to the PDC from the switch.

Low Pressure Clutch Cycling Switch (on top of accumulator);Is it possible that the pressure has dropped in the system and the switch will not kick the comp. on. Or wouldn't it need to at least kick the comp. on first to determine the pressure before cycling it off?

High Pressure Cutout Switch; Maybe the pressure has spiked and the switch will not allow the clutch to kick on?

Is the system not charged properly and there is not enough pressure to switch comp. on. Should I get the system evacuated and recharged?

BTW it was 115 degrees in Phoenix today! Shoot some ideas to me if you can please. It will be appreciated.
Thanks
Anthony

[MX-5]

From page 24-3 of the 2002 service manual:

If ambient is 110F,
Outlet temps should be <72F
High side pressure is 300-395psi
Low side pressure is 40-55psi

R134-A capacity is 1.875lbs. An ounce more or less will degrade performance.

From page 24-7:
NOTE: The refrigerant system does come from the
factory with a yellow tracer dye already installed to
aid in detection of leaks.

If the A/C system is not cooling properly, determine
if the refrigerant system is fully charged with
R-134a. This is accomplished by performing a system
Charge Level-Check or Fill. If while performing this
test A/C liquid line pressure is less than 345 kPa (50
psi) proceed to Empty Refrigerant System Leak Test.
If liquid line pressure is greater than 345 kPa (50
psi) proceed to low refrigerant level leak test. If the
refrigerant system is empty or low in refrigerant
charge, a leak at any line fitting or component seal is
likely. A review of the fittings, lines and components
for oily residue is an indication of the leak location.
To detect a leak in the refrigerant system, perform
one of the following procedures as indicated by the
symptoms.


The low pressure switch trips below 39psi
The high side switch is at 470psi

The PCM controls AC compressure activity.
It reads these inputs: TPS, RPM, AC switch, fin sensor, AC & fan relays.

[Cal Cruzer]

Sounds like a leak to me. If you don't have warranty left of testing equipment, I would just go to auto parts store and get a can of 134 and a filler and try charging it up to see if you can make it work.

[MX-5]

Cal,

How would you know EXACTLY how much to put in.

An ounce off-spec will degrade performance considerably.

I use a CPS / White Industries digital refridgerant scale. It's accurate with 1/10th of an ounce.



Please consider leaving AC work to us professionals.

[Ant]

Originally posted by MX-5
Cal,

How would you know EXACTLY how much to put in.

An ounce off-spec will degrade performance considerably.

I use a CPS / White Industries digital refridgerant scale. It's accurate with 1/10th of an ounce.



Please consider leaving AC work to us professionals.

If they recharged it with the wrong amount (1.56 lbs for the 2001) would this eventually lead to my condition? No clutch activation. I don't see if thats possible.

[MX-5]

From page 24-8 of the 2003 manual:

NOTE: Please refer to the underhood HVAC Specification
sticker for the latest refrigerant fill levels for
the vehicle being worked on.
NOTE: On vehicles equipped with the 2.4L Turbo
removal of the High Side Pressure Switch may be
required depending on your HVAC Charging Equipment.
Check your service equipment manual to see
if low side only servicing is permitted if not then
removal of the switch is required.

The turbo uses a different system with completley different pressures and capacities.



Page 24-27 of the 2001 service manual gives the total system capacity as 1.56lbs or 25oz or .709gramms.

So.... the capacity is changed for all 3 years and is even different for the turbo models.
This makes for complicated diagnosis.

[MX-5]

If an incorrect amount is charged, the low or high side pressures will be out of specs.

[slartyblarfast]

If your low side switch has gone bad that will also make it not work. I'm a DC techician and have run into this several times. Basically if the pressures are right in the system then thats probably what it is. Also understand that the low side switch controls the ground side for the compressor. Essentially what happens it that the computer doesn't see that the system has pressure so it doesn't turn the compressor on. Disconnect the low side switch a and jumper the pins. If it works and cools good then that's where the problem is. The Neon's are bad about this and our system is basically the same.

[Ant]

Originally posted by slartyblarfast
If your low side switch has gone bad that will also make it not work. I'm a DC techician and have run into this several times. Basically if the pressures are right in the system then thats probably what it is. Also understand that the low side switch controls the ground side for the compressor. Essentially what happens it that the computer doesn't see that the system has pressure so it doesn't turn the compressor on. Disconnect the low side switch a and jumper the pins. If it works and cools good then that's where the problem is. The Neon's are bad about this and our system is basically the same.

Great idea! Actually I was going through the schematics and operation of the system and decided (while I was sleeping last night) that this would be the next logical step. So I jump the terminals and BINGO, comp. kicks on.
So I know comp. is good. It is either the low press. switch or the system was not charged correctly. I vote for the latter.
I will throw the manifold gauges on to confirm the pressure readings are indeed too low to operate the clutch.
Is there anyway to tell how much R134 was added, or do I need to have the system recovered and start over with the exact amount???
Thanks for you responses gentlemen

[MX-5]

Originally posted by Ant
Is there anyway to tell how much R134 was added, or do I need to have the system recovered and start over with the exact amount?

From page 24-4 of the 2002 manual:

STANDARD PROCEDURE - CHARGING A/C
SYSTEM

PARTIAL CHARGE

This vehicle does not have a sight glass. It is not
possible to determine the amount of (R-134a) charge
in the system. Therefore it is necessary to completely
evacuate and recover the system, and then recharge
the system fully.

So... you have to start over.