Air Conditioning Won't work

joshheat25:

What did the shop do? If they were working in the vicinity of the compressor, the plug might be disconnected. Worse, they could have punctured one of the A/C lines. If they weren't working around there, then check the fuse first.

There's a pressure switch near the bottle on the passenger side up near the firewall. That pressure switch is a problem child in our cars. It is inexpensive to replace (there's a Schrader valve in the connection that prevents the refrigerant from coming out when you unscrew the old one and install the new one).

There is a way to check if the switch is faulty but I do not recall the method. You might try to run a search ("low pressure switch") and see what pops up.

HTH,

Chris

Why not just take it back to the shop and have them fix it? If the A/C worked when you took it in then it should work when you get it back. There a some exceptions to that, but still, you should take it back to them and have them look at it.

Were you able to get this fixed? I have a 2000 3.8L Mustang with the same problem (no cool air).

I thought it was low on freon, but when I had it checked, it was full. I was told the compressor wasn't turning on. I've been putting off taking it to a repair shop because I fear it'll be expensive.

Can anyone tell me which fuse I should be looking at?

Thanks.

Dan

dmclamb:

It may be the pressure switch up by the passenger side firewall near the A/C "bottle". Others have had the same problem. When it fails, it prevents the compressor from coming on. There's a Schrader valve in it so you unscrew the old one and put the new one on and you should be good to go. I don't have the fuse diagrams at the moment (sorry).

HTH,

Chris

Thanks Chris.

I dug out my manual and checked all the fuses`that sounded related to the A/C in the cab and under the hood. All were fine.

I then removed the existing pressure switch from the compressor, went to my local parts store, and ordered a replacement. It should be here in a couple of days - I'll post the results.

Now to figure out why there's a 5 - 10 minute delay before my odometer comes on. . .

Appreciate the help.

Dan

Here's a list of things to check and how to check them.

1. A/C clutch coil itself. You can use a voltmeter across the two terminals on the compressor connector. Should not be open. As an alternative, connect +12v to one of the pins, ground the other and see if the compressor clutch "snaps closed". If so, the clutch is good.

2. high-pressure cutoff switch is near the radiator on left side. It has 4 pins, two for the clutch, two for the fan. Chilton's gives the color coding. Jumper across the two compressor pins. If the compressor comes on, the high-pressure cutoff switch needs to be replaced.

3. If that fails, check the pressure cycling switch, on the accumulator/drier over on the passenger's side next to the firewall. Disconnect the connector and jumper between the two pins. If the clutch engages, replace the switch.

4. If that fails, check the same connector to see if you get +12 volts between one of the pins and ground (test both, one should be +12). If so, then the most likely candidate is the CCRM which is inside the passenger's side fenderwell. It is a 150 buck box that contains the A/C relay, fan relay, fuel pump relay, etc. But you have to replace it as a unit. If you don't get 12 volts across the cycling switch, you probably are left with a blown fuse or a switch problem in the dash.

The circuit is pretty simple. +12 comes from the A/C switch on the dash, and goes in series thru the cycling switch, the high-pressure cutoff switch, and to the relay in the CCRM before arriving at the clutch coil. If any of those are bad, no A/C. If the clutch coil goes out, it can burn the relay in the CCRM, which means replacement.

All of this assumes a good charge, somewhere between 70 and 120 psi with the motor turned off, measured on either line since they should be equalized. Cool morning = 70psi with a normal charge. Hot at noon can go to 120psi or so. Low pressure (well below 70) will prevent it from coming on... So you need a good R134a charge before testing anything else.

It is a simple system, and with a good chiltons/haynes book to give you the color coding, it is not hard to follow the wiring, and find/fix the bad component.

i have ac cycling switches dirt cheap, used, but they work just fine. id obviously test it first. pm me if interested

Bob - thanks for the comprehensive summary!

If the replacement pressure switch doesn't do the trick, I'll get a Chilton manual and, using it and your notes, see what I can do.

Dan

dmclamb said:

Bob - thanks for the comprehensive summary!

If the replacement pressure switch doesn't do the trick, I'll get a Chilton manual and, using it and your notes, see what I can do.

Dan

Click to expand...

The more common mode of failure I have seen on the cycling switch is that it cycles _way_ too frequently. Low pressure should swing between something like 22 and 35. If the switch goes bad, it will hang right at 20-22 PSIG with the compressor going off and on like mad, which will damage the clutch given enough time. Last one we saw was in a 2000 my son owns and it felt like it was missing it was going on and off so quickly...

But we also found a bad CCRM in his 2000 last year, so that is a candidate as well. This can be a "cascading" problem if you are not careful. rapid cycling produces lots of heat in the clutch. This can damage the coil that engages the clutch, causing it to short internally as the wires lose insulation. If enough coils short out, the clutch slips more due to reduced field strength. This increases current draw since some of the coil becomes shorted. This causes heat and excessive draw thru the relay in the CCRM, which can fry the contacts so that they barely make a connection, and won't pass enough current to snap a good clutch closed, eventually these points burn out and you are done. And if you don't get all the guilty parties replaced, it is waiting to happen again... and again...

I opened up the CCRM (drill four rivets) and saw the A/C relay plastic enclosure was melted in one side and the circuit board underneath was not green but brownish in color. Three of the realys are BOSCH units. The other two are smaller ones. You can replace the burnt realy or buy the whole thing. I put the CCRM back together and will replace it with a new one this weekend.

Cheers... Ric.

Hardtop68 said:

I opened up the CCRM (drill four rivets) and saw the A/C relay plastic enclosure was melted in one side and the circuit board underneath was not green but brownish in color. Three of the realys are BOSCH units. The other two are smaller ones. You can replace the burnt realy or buy the whole thing. I put the CCRM back together and will replace it with a new one this weekend.

Cheers... Ric.

Click to expand...

That's caused by excessive current draw. Before replacing, you need to figure out why that is happening, or you will make the CCRM part a best-seller for Ford as you will be buying another soon. I made a dummy jumper insert and used a 5a fuse, and debugged until I figured out why a 5a fuse would blow. with things working correctly, the 5a fuse is more than enough for the compressor clutch. If it isn't there a significant drain somewhere, most likely either in the clutch coil itself, or in a short where the wire has rubbed against something for too long.

No luck with a new pressure cycling switch. Darn.

I wish it wasn't 100 degrees outside.

If I had more time, tools, and the resources to do the work, I'd dig deeper and try to fix it myself, but I may end up having to take it to a shop. My wife and I just had a baby, so my time is really limited right now.

I'll post what I ended up doing to get this fixed before it's all over, even if it that means it ends up being sold.

Thanks again for your help!

I replaced the CCRM and everything is OK... Next week I will replace the leaking evaporator core... I hope the refrigerant charge lasts until then...

DMCLAMB... hope you find someone close to were you are to help you fix this... get the CCRM and the case of beers... last week I replaced a friends 96 GT vert leaking intake manifold for the new aluminum crossover... I always get calls to fix my friends rides...

BOB... you are right... first thing to do is check for the root cause of the failure... I let the A/C to cycle a lot just before the relay got burnt, and two or three times some time ago... I knew that it was cycling a lot and something was going to give someday (realy and/or clutch coil.) Nowadays, evaporator cores are designed to last 2 years only!

I will replace the 15A fuse for a 5A one as you did just to be sure. My car has 208.000 km on the odometer (that is aprox. 131,000 miles) and we use the A/C at all times. Over here there is no winter and temperature is always above 30°C or 86°F all year long with hottest days up tp 45°C or 113°F...

Thanks a lot...

Hardtop68 said:

I replaced the CCRM and everything is OK... Next week I will replace the leaking evaporator core... I hope the refrigerant charge lasts until then...

DMCLAMB... hope you find someone close to were you are to help you fix this... get the CCRM and the case of beers... last week I replaced a friends 96 GT vert leaking intake manifold for the new aluminum crossover... I always get calls to fix my friends rides...

BOB... you are right... first thing to do is check for the root cause of the failure... I let the A/C to cycle a lot just before the relay got burnt, and two or three times some time ago... I knew that it was cycling a lot and something was going to give someday (realy and/or clutch coil.) Nowadays, evaporator cores are designed to last 2 years only!

I will replace the 15A fuse for a 5A one as you did just to be sure. My car has 208.000 km on the odometer (that is aprox. 131,000 miles) and we use the A/C at all times. Over here there is no winter and temperature is always above 30°C or 86°F all year long with hottest days up tp 45°C or 113°F...

Thanks a lot...

Click to expand...

The biggest problem is that the GDMF tree huggers made us switch from a very reliable R12 system to R134a which has increased pressure, and is more corrosive than R12. As a result, evaporator core failures are common, and expensive. In my old dodge dakota, the shop wanted 13 hours of labor. It took me about 10 hours over 2 days, but the cost was zero except for the part.

The problem with this (and the reason for my GDMF expletive above) is that we were switches from R12 because it breaks down into chlorine and other components, and free chlorine is damaging the ozone. Problem with this is that 99+% of the free chlorine in the atmosphere comes from seawater which has NaCl (salt, combination of chlorine and sodium) that breaks down in sunlight. Rather than switching us to a different refrigerant, the idiot tree huggers should have been petitioning for plastic films spread over the surface of the ocean.

But we are stuck with the fallout. R134a is not as efficient as R12, the pressures are elevated, it is more corrosive and attacks the evaporator core metal, etc. Only plus is it made some companies a small fortune...

nyuk98gt said:

joshheat25:


There's a pressure switch near the bottle on the passenger side up near the firewall. That pressure switch is a problem child in our cars. It is inexpensive to replace (there's a Schrader valve in the connection that prevents the refrigerant from coming out when you unscrew the old one and install the new one).

There is a way to check if the switch is faulty but I do not recall the method. You might try to run a search ("low pressure switch") and see what pops up.
Chris

Click to expand...

+1. I had that same symptoms. I had a faulty switch on a 97 Cobra. I didn't believe my friend at work who told me to change that. I changed it and sure enough, I got the A/C working. ANY Ford will work. I grabbed a used one from a Windstar.

joshheat25 said:

Problem NOT Solved... darn it

OK The compressor now will kick on... I bought a can of refridgerant with a pressure gauge. Now the Compressor clutch will engage for about 1 second and kick right back off and it keeps repeating this it'll kick back on every 5 seconds for 1 second then stop.

ALSO looking at the pressure gauge when it does this. The pressure gauge will go from 35 - 45 as if the compressor is charging the system then it stops.

I also tried unplugging the switch on top of the condenser I belive.. right next to where I was adding R134 and then it wouldn't even come on at all. Soo What is wrong?

Click to expand...

Disconnect the connector at the cycling switch on the drier near the firewall. On the dangling connector, short the two terminals together with a short piece of wire or a paper clip. If the compressor now runs all the time (do not run it like this for more than a couple of minutes) then you have one of two choices...

Either the switch is bad, or your freon charge is way low. With the motor off, the system pressure should be in the area of 70-120psi depending on outside temp. 70 is normal for a fairly decent morning outside temp. Those are the only two choices since you have verified that the compressor comes on and stays when the switch is shorted closed (note that the jumper goes in the connector to the switch, not the switch itself which is useless with the connector removed...

If the compressor does not run with the cycling switch bypassed, then try the high-pressure cutout switch which is up near the radiator... It is a 4-wire connector, but a good haynes book tells you which two pins are the high-pressure cutout and which two are the fan-on switch. Short the A/C pins and if it now runs, again you have two choices...

Freon charge is way too high, causing way high static pressure, or else the switch is bad and thinks the pressure is too high when it is not...