Compressor isn't engaging

[gpking]

My A/C hasn't worked reliably since I picked up my TB this past July. It would work occasionally, but usually kicked off or blew lukewarm air leading me to believe it needed freon.
Defrosting has worked fine all winter.

With spring quickly approaching, I decided I'd refill the freon and make sure my a/c works this summer.
I put on my a/c and it stayed on, but my compressor isn't spinning. I checked the coolant reservoir and it's about 1/2 full.

Knowing little about a/c maintenance, what should I do next? My understanding is I cannot refill the freon without the compressor running.

 

[The_Roadie]

You should never just add freon. Too much will make the system not work as designed, and if you think you have too little, you have to find and fix the leak first. That involves having someone with a freon recycling system pump it out first, then pull a vacuum, locate the leak, fix it, then refill the system with the exact number of ounces of refrigerant and lubricating oil the manual calls for. Not a DIY driveway projecy, unless you really want to buy the equipment and gauges for one time use.

You can get gauges to measure the high and low pressure, but as you noted, it's hard to troubleshoot without the compressor running.

That said, assuming you have any decent amount of refrigerant at all in there, the most common failure item is the low pressure cutoff switch plugged into a test port on the side of the receiver/dryer on the passenger side of the firewall. That's the polished aluminum can that gets frosty when the system's running. Swap that as a shotgun experiment, or get to a trusted professional AC shop.

The coolant reservoir isn't related to the AC system. But while we're on the subject, did you remove the radiator cap and confirm the level and nature/color of the coolant in the radiator?

 

[gpking]

You should never just add freon. Too much will make the system not work as designed, and if you think you have too little, you have to find and fix the leak first. That involves having someone with a freon recycling system pump it out first, then pull a vacuum, locate the leak, fix it, then refill the system with the exact number of ounces of refrigerant and lubricating oil the manual calls for. Not a DIY driveway projecy, unless you really want to buy the equipment and gauges for one time use.

You can get gauges to measure the high and low pressure, but as you noted, it's hard to troubleshoot without the compressor running.

Thank you for your advice. It's so hard to find reliable information on the internet about fixing the a/c.
At this point I feel like it would be best to just throw in the towel and take it to a professional.

That said, assuming you have any decent amount of refrigerant at all in there, the most common failure item is the low pressure cutoff switch plugged into a test port on the side of the receiver/dryer on the passenger side of the firewall. That's the polished aluminum can that gets frosty when the system's running. Swap that as a shotgun experiment, or get to a trusted professional AC shop.

I don't think it is the switch. The previous owner noted the A/C was loosing it's cool, which my limited understanding leads me to believe there is in fact a leak.
I would guess a faulty switch would cause intermittent a/c functionality, not a gradual decline in coolness and ultimately the inability to function?

The coolant reservoir isn't related to the AC system. But while we're on the subject, did you remove the radiator cap and confirm the level and nature/color of the coolant in the radiator?

I'm working on it. The reservior cap came off no problem but the radiator cap doesn't want to budge. I'll go give it another shot after I finish typing this.

 

[c0a8l0v6i8n9]

The compressor will not engage under 40 degrees.

 

[gpking]

The compressor will not engage under 40 degrees.

But I thought it engages when in defrost?

It's hovering around 40° right now, so I'll give it a shot tomorrow when it'll be in the high 50's.

 

[The_Roadie]

There is no temperature sensor that suppresses the compressor under 40 degrees. There are refrigerant pressure sensors that accomplish about the same thing, but allow for short automatic compressor blips every few seconds in lower temps. And as you remember, this allows dehumidification of cabin air even when it's cold. If you manually turn the AC compressor off by hitting the little snowflake symbol, recirculate and defrost modes override that and the compressor starts cycling again.

 

[KNBlazer]

In my experience, in a non trailvoy, my compressor would not kick in because it was low on freon, as soon as I added some it started cycling... as it was suggested, I would first get a gauge to see how much is actually in the system, then if it's low, look for an a/c dye you can add into the system... fix the problem yourself, then go to a shop to pull vacuum and recharge it yourself at home....

 

[gpking]

Regardless, more research has kept me convinced I need to get this done right.
If freon can leak out of the system then air and contaminants can also get in.

I'd rather fork over the money up front instead of cheaping out and needing to replace a dead compressor in the future.

 

[The_Roadie]

Been working on vehicles for 50 years. Almost all possible systems. But I draw the line at AC (never bought the pump and full gauge set, and I have a trusted professional to go to), and dropping the pan on an automatic tranny. (A college accident under my Opel Kadette left me with a phobia about drowning in transmission fluid.)

 

[AtlWrk]

There is no temperature sensor that suppresses the compressor under 40 degrees.

The PCM ultimately decides whether or not to engage the compressor based on a laundry list of conditions. Coincidentally, the first of which (from AllDataDIY):

"The following conditions must be met in order for the A/C compressor clutch to turn ON:
•Ambient air temperature above 1°C (35°F)"

Not saying I agree, just that this information is out there...

I'm not even sure I believe this since I could swear I saw my A/C cycling a few days ago in the driveway in the bitter cold. Then again the IAT sensor does tend to run +10F+ warmer than true ambient... more GMT360 curiosities

 

[c0a8l0v6i8n9]

The PCM ultimately decides whether or not to engage the compressor based on a laundry list of conditions. Coincidentally, the first of which (from AllDataDIY):

"The following conditions must be met in order for the A/C compressor clutch to turn ON:
•Ambient air temperature above 1°C (35°F)"

Not saying I agree, just that this information is out there...

I'm not even sure I believe this since I could swear I saw my A/C cycling a few days ago in the driveway in the bitter cold. Then again the IAT sensor does tend to run +10F+ warmer than true ambient... more GMT360 curiosities

This comes straight from the owners manual

 

[Texan]

Regardless, more research has kept me convinced I need to get this done right.
If freon can leak out of the system then air and contaminants can also get in.
{/QUOTE]

Without knowing more about the history of the system and the miles on the vehicle, it is hard to
guess what the problem is. As long as the Freon system has a positive pressure, it is almost
impossible for air or moisture to get in it. The compressor clutch air gap can get wider with wear
and not engage constantly. Just trying to help.

 

[The_Roadie]

...more GMT360 curiosities

The day I don't learn something new about stuff, I die. This vehicle's added ten years to my life already! :wootwoot:

 

[KNBlazer]

if you take it to a shop, I wouldn't be surprised if they give you a $1k estimate....

 

[triz]

Sounds like the compressor is going. Any weird noises coming from it? Mine seized up and snapped my belt.

 

[C-ya]

Then again the IAT sensor does tend to run +10F+ warmer than true ambient...

I have seen this as well, but the IAT and ambient sensors are different sensors. I have seen my IAT run 40+ degrees higher than ambient back in the summer.

 

[c0a8l0v6i8n9]

Unplug the connection at the low pressure switch. This is by the radiator overflow and connect a paper clip into the connector on the wire. This will jump the compressor on. If it doesn't turn on then you have a bad compressor.

 

[jimmyjam]

uh oh, its the nitpick police! hands up!

You should never just add freon.

you should never add freon, period! freon is dupont's brand name for R22. the politically correct term is refrigerant

you have to find and fix the leak first. That involves having someone with a freon recycling system pump it out first, then pull a vacuum, locate the leak, f

not sure how to locate a leak with the system under vacuum, what you want to pressurize the system with nitrogen. then dab soapy water around and look for the bubble factory

carry on, and keep it legal

 

[MAY03LT]

if you take it to a shop, I wouldn't be surprised if they give you a $1k estimate....

Me neither....my work is $139.95 just to hook up the gauges.

The compressor clutch air gap can get wider with wear and not engage constantly.

I'm hesitant to post this because of the potential danger to casual DIY'ers, but I politely smack the clutch with a hammer when I suspect that the gap is too wide.

Not a DIY driveway project, unless you really want to buy the equipment and gauges for one time use.

As a reference, I have about $300 invested in my at-home A/C tools and still have to use an outside shop to evacuate/recycle the system.

 

[The_Roadie]

uh oh, its the nitpick police! hands up!

Shoot! That's typically ME. I even thought about it as I was typing it. And used the longer and correct word later. Just failed to go back and replace "freon" later.

not sure how to locate a leak with the system under vacuum,

What I meant to say with amplified detail (which may still be wrong, but I read it somewhere...) was most systems that used to work and deteriorated over a long period of time don't have a gross leak you can detect with pressure and looking for UV dye or a soapy water solution. Those systems you can confirm they are gross leak-free by pulling a hard vacuum, closing off the system, and making sure the vacuum stays there for an hour or so. Many sites have lot longer write-ups than we can do here, and are trivial to Google for.

As a reference, I have about $300 invested in my at-home A/C tools and still have to use an outside shop to evacuate/recycle the system.

Sez the guy with his own Tech II.

Wish you lived closer.

 

[jimmyjam]

Shoot! That's typically ME.

which is why i couldn't help myself

Those systems you can confirm they are gross leak-free by pulling a hard vacuum, closing off the system, and making sure the vacuum stays there for an hour or so.

when I assemble a system I feel confident that if it holds vacuum for an hour or so then its good, but I don't know how you'd determine where the leak is without pressurizing it

 

[gpking]

Unplug the connection at the low pressure switch. This is by the radiator overflow and connect a paper clip into the connector on the wire. This will jump the compressor on. If it doesn't turn on then you have a bad compressor.

Thank you for this useful tidbit of information.

Fortunately for me my 3rd cousin (or something like that) is a mechanic and he owes me a favor, so it looks like I'll have some free professional help.
He started talking about r134a and o-rings leaking and sealant so he seems to know what he's doing.
Luckily for my wallet, we'll get this sorted out for just the price of materials and maybe I'll learn how to do it myself in the future.

 

[meerschm]

Jumping around the low pressure switch only works if the rest of the system is operating as designed.

there are at least two sensors, and lots of logic, and a relay before you get power applied to operate the compressor clutch.

your mechanic cousin may be capable of figuring all this out.

so two sets of issues.

first is if there is any R134a in the system. (pressure gauge required)


second is test to see if power is applied to the compressor clutch (meter can do this, requires some know how) also the right scan tool set can help.

if power is applied, but the clutch does not operate, it is possible to replace just the clutch, or to remove a shim to make life easier on an old, weak, coil.

have fun, and remember is still a couple months before it will really get hot.

 

[AtlWrk]

I have seen this as well, but the IAT and ambient sensors are different sensors. I have seen my IAT run 40+ degrees higher than ambient back in the summer.

In the case of my 2006 LS (manual HVAC) there is no separate ambient temperature sensor. The IAT sensor integrated in the MAF was it. "Was" because I did add one later but it is connected to and serves only the compass/temp rearview mirror (how I know it wasn't there in the first place).

If the OP's system was marginal because of low refrigerant in the July heat, it would only make sense that it would be worse in the cold temps where the "resting" system pressure is even lower. If it were me, I would briefly ground the clutch relay control signal to verify that the clutch is electrically and mechanically functional. Only then I would start looking to a shop to diagnose leaks/pressures.

 

[Gevans17]

checked for blown fuses? Had similar issue in another vehicle. turned out to be an electrical short in the compressor clutch coil.

 

[Gearheadvr4]

It's not that difficult to do yourself with a little DIY knowhow. You need to replace the drier and pull a full vacuum to do this correctly. The vacuum is essential to pull the air out that you let in. Also it's important is to pull out the moisture. Anything beside r134a and oil in your system will kill the compressor faster and make it cool less efficiently.

Makes me laugh when I hear people at the local auto parts store just topping off their AC system with a new can of air. AC systems are not designed to ever leak. If you have to "top it off for the summer" then obviously you have a leak. The system will cool progressively less and less and overwork the compressor. Also, the oil will turn acidic when exposed to air and again rapidly destroy the compressor

I purchased the gauges and made my own vacuum pump with an old deep freeze compressor. Brazed on my own fittings. Here in TX there is no chance I'd go without AC.



I know this is probably way more info than you need, but just in case any of you go the DIY route

COMPRESSOR
The compressor is responsible for compressing and transferring refrigerant gas. The A/C system is split into two sides, a high pressure side and a low pressure side; defined as discharge and suction. Since the compressor is basically a pump, it must have an intake side and a discharge side. The intake, or suction side, draws in refrigerant gas from the outlet of the evaporator. Once the refrigerant is drawn into the suction side, it is compressed and sent to the condenser, where it can then transfer the heat that is absorbed from the inside of the vehicle.

CONDENSER
The condenser is the area in which heat dissipation occurs. The condenser will have much the same appearance as the radiator in your car as the two have very similar functions. The condenser is designed to radiate heat. Condensers must have good air flow anytime the system is in operation. On our Legends, the condenser air flow is supplemented by the electric cooling fan(s). As hot compressed gasses are introduced into the top of the condenser, they are cooled off. As the gas cools, it condenses and exits the bottom of the condenser as a high pressure liquid.

RECEIVER-DRIER
The receiver-drier is used on the high side of systems that use a thermal expansion valve, as in our Legends. This type of metering valve requires liquid refrigerant. To ensure that the valve gets liquid refrigerant, a receiver is used. The primary function of the receiver-drier is to separate gas and liquid. The secondary purpose is to remove moisture and filter out contaminants. The receiver-drier has the sight glass in the top. This sight glass is often used to charge the system. Under normal operating conditions, vapor bubbles should not be visible in the sight glass. The use of the sight glass to charge the system is not recommended in R-134a systems as cloudiness and oil that has separated from the refrigerant can be mistaken for bubbles. This type of mistake can lead to a dangerous overcharged condition. There are variations of receiver-driers and several different desiccant materials are in use. Some of the moisture removing desiccants found within are not compatible with R-134a. The desiccant type is usually identified on a sticker that is affixed to the receiver-drier. Newer receiver-driers use desiccant type XH-7 and are compatible with both R-12 and R-134a refrigerants.

PRESSURE REGULATING DEVICE
Controlling the evaporator temperature is accomplished by controlling refrigerant pressure and flow into the evaporator.

THERMAL EXPANSION VALVE
The refrigerant regulator used in our Legends is the thermal expansion valve, or TXV. Commonly used on import and aftermarket systems. This type of valve can sense both temperature and pressure, and is very efficient at regulating refrigerant flow to the evaporator. This type of valve, although efficient, has some disadvantages over orifice tube systems. Like orifice tubes these valves can become clogged with debris, but also have small moving parts that may stick and malfunction due to corrosion.

EVAPORATOR
Located inside the vehicle, the evaporator serves as the heat absorption component. The evaporator provides several functions. Its primary duty is to remove heat from the inside of your vehicle. A secondary benefit is dehumidification. As warmer air travels through the aluminum fins of the cooler evaporator coil, the moisture contained in the air condenses on its surface. Dust and pollen passing through stick to its wet surfaces and drain off to the outside. On humid days you may have seen this as water dripping from the bottom of your vehicle. Rest assured this is perfectly normal. The ideal temperature of the evaporator is 32° Fahrenheit or 0° Celsius. Refrigerant enters the bottom of the evaporator as a low pressure liquid. The warm air passing through the evaporator fins causes the refrigerant to boil (refrigerants have very low boiling points). As the refrigerant begins to boil, it can absorb large amounts of heat. This heat is then carried off with the refrigerant to the outside of the vehicle. Several other components work in conjunction with the evaporator. As mentioned above, the ideal temperature for an evaporator coil is 32° F. Temperature and pressure regulating devices must be used to control its temperature. The pressure regulating device, in our case the TXV, functions to keep pressure in the evaporator low and keep the evaporator from freezing; A frozen evaporator coil will not absorb as much heat.

 

[LikeEnvoy]

The compressor will not engage under 40 degrees.

Glad I saw this- I have been finding my windows are misting up (winter, but it started to snow again) so pushed the AC button on but it didn't seem to help- still misty windows. I checked the AC clutch and the front plate was NOT spinning. Worried it was faulty until I saw this post. It's likely that although a warm front brought snow it was still below 40°F.
I'll test again when the outside temp climbs above this.

 

[coolasice]

Glad I saw this- I have been finding my windows are misting up (winter, but it started to snow again) so pushed the AC button on but it didn't seem to help- still misty windows. I checked the AC clutch and the front plate was NOT spinning. Worried it was faulty until I saw this post. It's likely that although a warm front brought snow it was still below 40°F.
I'll test again when the outside temp climbs above this.

The following conditions must be met in order for the ECM to turn on the compressor clutch:
• Battery voltage is between 9-18 volts
• Engine coolant temperature (ECT) is less than 123°C (253°F)
• Engine speed is greater than 600 RPM
• Engine speed is less than 4,760 RPM
• A/C high side pressure is between 2929-269 kPa (39-425 psi)
• Throttle position is less than 100 percent
• Evaporator temperature is greater than 0°C (32°F)
• ECM does not detect excessive torque load
• ECM does not detect insufficient idle quality
• The ambient temperature is above 1°C (34°F)