A/C stops blowing cold after driving 10 m

RYAN1225

MEMBER
2000 DODGE DAKOTA
V8
2WD
AUTOMATIC
150,000 MILES

A/C will blow cold for the first 10 - 15 minutes or so of driving. If the outside temperature rises above 80 deg it only last a few minutes. After that, it occasionally blow cold again for about a minute or so then back to blowing air at about 75 deg. Also, the air smells stale during this time.

So far I have replaced the compressor clutch switch on the drier.

I live in Houston, so right now it is getting pretty hot out and always very humid.

7 Replies

CARADIODOC

MECHANIC
33,916 POSTS

Hi ryan1225. Welcome to the forum. This sounds typical of low charge. If you can buy a can of R-134 and you know how to install the refrigerant safely, you should see a big change.

Caradiodoc

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Thursday, May 6th, 2010 AT 3:32 PM

RYAN1225

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I had a new liquid line and clutch cycle switch put on a few months ago. They also recharged the system completely. You think I might have a leak? The truck only gets driven about 3-4 times a month. What can I use to test for a leak?

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Thursday, May 6th, 2010 AT 3:41 PM

CARADIODOC

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At ten years old, normal leakage can be expected to cause poor cooling, but if parts were replaced recently, the system would have been fully recharged. The first place to look is at the connections of the new line. You might be able to see it by mixing a little water and dish soap and wiping it on the joints. That will work on other connections too, but for inaccessible locations such as the front seal in the compressor you will need an electronic leak detector. It has a wand with a sensor that actually measures the absence of oxygen. You might be able to borrow one from a local auto parts store.

Caradiodoc

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Thursday, May 6th, 2010 AT 10:44 PM

RYAN1225

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9 POSTS

Ok. I rented some manifold gauges this weekend to test the system. I tested it after I drove home from work so it was at normal operating temp. Of coarse it was working just fine during initial testing, as this is an intermittent problem. I drove it around the block and came back and hooked the gauges up again. When I hook up the gauges, my service manual says to pull the low pressure clutch cycling switch connector and install a jumper wire between the two connectors. I had done that before when everything was working well. This time however, the clutch would not engage and that's when it wasn't blowing cold inside the truck. I checked to see if I had a good connection and I did. I got my multimeter and checked the connector and had battery voltage on one side and ground on the other.

So, now I'm pretty convinced that either I have a bad compressor or clutch. My question to you is how do I tell if it is the compressor or the clutch and can I just replace the clutch by itself, or do I need the whole set-up?

Thanks,

Ryan

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Sunday, May 9th, 2010 AT 6:55 PM

CARADIODOC

MECHANIC
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Dandy testing! If you have voltage and ground, logic dictates the coil in the clutch must be open, but after fixing tvs and vcrs for over 34 years, I've been bitten many times by logic. Use your meter to measure the resistance of the clutch coil. You can expect somewhere between, ... Oh, ... 4 to 12 ohms I would expect. If it measures about in that range, use a pair of small jumper wires to connect direct battery voltage to it. If it engages that way but not when connected normally, you may have been tricked by your meter. I've seen some really sharp mechanics go down the wrong road because of misleading readings.

Instead of your meter, use a test light to measure for voltage, then move the clip lead to the battery positive post and use it to measure the ground wire. If there is a break in one of the wires, the test light will not be able to get enough current to light up, but if just a tiny taste of current trickles through a carbon track, say in a corroded splice for example, that will be enough for the voltmeter to pick it up and show a reading.

As for replacing the clutch, you can leave the compressor on the engine and just slide the clutch assembly off. I have a former student who coincidentally just replaced his clutch on his 2000 Dakota V-6. His had a bad bearing though. The coil was ok. You will need a special puller that you can borrow from some parts stores. It just threads into the center of the assembly, then tightening the center bolt pulls the unit off.

Caradiodoc