05 DeVille - No A/C

[Brobichaud]

Recently purchased - no history with vehicle.

A/C Compressor not clutching in.

Underhood fuse no. 26 is good. Relay no. 32 is good.

No codes, other than IPC U1000.

Where should I look next?

[barczy01]

Does the system have freon in it? Whats the outside temp sensor read on HVAC control head? Any system codes?

[Brobichaud]

Don't know if it has freon in it. Not sure how to tell.

I would expect a code if it didn't. No codes.

Outside temp 75. Thermostat set at 60.

Thanks!

[Brobichaud]

Is there a DIY way to tell if there is freon in the system?

Would there be a code if it was low on freon?

[KHE]

Usually, a dual zone system will be warm on one side and cool on the other side before the system sets the low refrigerant code.

With the A/C turned on, is the compressor clutch engaged? Feel both evaporator pipes - are they cold to the touch or is the outlet warmer than the inlet?

You really need a gage to check the high and low side pressures.

[Brobichaud]

Dual zone system was warm on drivers side and HOT on passenger side.

I replaced the passenger side blend door actuator, now it is warm on both sides.

Compressor clutch does not engage. Fuse and Relay are good. No codes.

[KHE]

Inspect the case of the compressor - if it is all oily, the case seals may be leaking and the system is low on refrigerant.

Do you have access to a set of refrigerant gages? The static pressure reading would either confirm a low refrigerant condition or point to another diagnostic method.

[Brobichaud]

Compressor Case is clean - Actually looks new.

Inline Guage on R134a refill can indicates 36 lbs (system filled) with compressor not turning.

Now I really don't know where to look next.

Fuse good. Relay good. No DTC Codes. System filled. Compressor not clutching in.

[KHE]

If the static pressure is 36 psi (which from your description is what you measured), the system is very low on refrigerant and it should have set a code and diaplayed the LOW REFRIGERANT message on the information center. At 75° outside temperature, the static pressure should be around 70psi. There is a refrigerant leak in the system somewhere.

It is impossible to asses the state of the charge with those low side only gages. Without monitoring both the low and high side pressures, the system can get over-filled and the high side pressure can reach the point where the pressure relief valve opens or a hose bursts. Gages are useful for troubleshooting the system and getting the charge close but the only accurate way to determine the state of the charge is to recover it with a recovery/recycling machine and weigh the amount of recovered refrigerant.

[Brobichaud]

Thank you for the info. Strangely enough, it is starting to make sense.

The system is apparently low on refrigerant, most likely due to a leak.

The low refrigerant situation is preventing the compressor from engaging.

Although I currently have no codes; when I got the car, 2 weeks ago, it displayed 26 codes including P1531 (A/C Low side Temperature Sensor Fault).

Maybe this is why I am not getting a LOW REFRIGERANT code?

I am thinking I need to replace the Sensor and then have the system leak checked/evacuated/refilled.

Any idea where the Sensor is hidden?

[KHE]

The A/C temperature sensors are in the refrigerant line that runs along the firewall. The refrigerant needs to be recovered before replacing the sensors. The sensors rarely go bad - most of the time, if they're bad it is because someone installed the orifice tube backward and the sensor was damaged. This was common in the earlier cars - I believe the orifice tube is in a different location in the 2000+ Devilles though. Was the sensor code current or history?

[Brobichaud]

The code was History. It has not returned in two weeks.

Any idea how I could have low refrigerant, but no A/C related codes?

[KHE]

I do not know why the low refrigerant code is not set. That is strange.

One thing to verify is that the compressor clutch is plugged in but the low static pressure indicates a low refrigerant charge.

[Brobichaud]

Update! I was shocked to hear the compressor clutch in, so I gave the system a shot of refrigerant.

Now my static pressure is 70 lbs. with an under-hood temperature of about 80 deg.

The low side pressure with the compressor running is 30 lbs.

The smaller diameter evaporator line is cold to the touch at the firewall.

The larger diameter line (return?) is warm.

Nedless to say, the vents are blowing warm air.

Still no codes, but at least the compressor is running. Something blocked?

BTW, Thank you for you help thus far!

[KHE]

If you are feeling the lines right at the firewall, I'd say there is a low refrigerant charge - both pipes should be approximately the same temperature.

[Brobichaud]

Adding refrigerant appears to be a slow process.

Current static pressure is 70 psi @ temp of 80 deg. Pressure with compressor running is 34 psi.

While adding refrigerant, pressure occasionally spikes to 60 - 70, but quickly returns to 32-34 with a noticeable compressor 'click'. Hope this is normal.

Return pipe from evaporator remains warm.

It is probably time to either bring it to someone who knows what they are doing or buy a set of guages - both of which appear pricey.

[KHE]

I think it is time to take the car to an A/C shop. Without the proper tools it will be difficult to solve the problem. After you get the car back from the shop, please post what the fix to the problem was so others may learn from the process.

[Brobichaud]

Bought a set of guages!

Static: Low side = 72 psi., High side = 75 psi. Garage temp = 76 deg.

Operating: Low side = 26 psi., High side initially 160 - 175 psi. but after a few minutes drops off to 100 psi.

Low side increases to 40 - 45 as compressor cycles off. High side does not change as compressor cycles off.

Smaller diameter evap line is COLD. Larger diameter evap line is warm.

Hope this tells us something useful.

[KHE]

Depending on the relative humidity, the shop manual states the following for 76° ambient temp:

Below 35%: Low side 28-46 psi; High side 119-194 psi

35-50%: Low side 31-47 psi; High side 123-192 psi

Above 50%: Low side 33-51 psi; High side 122-189 psi

From your post, the line that is connected to the low side gage port that goes to the evaporator is cold but the return line is hot - It appears that the system is low on refrigerant to me. Why it did not set a code is still a mystery.

You can connect the can of refrigerant to the manifild gage set and bleed off the air. Make sure both gage valves are closed. Have a helper start the engine. DO NOT UNDER ANY CIRCUMSTANCES OPEN THE HIGH SIDE (RED) VALVE ON THE MANIFOLD GAGE SET. With the can upside down, open the LOW (blue) side valve slightly and the system will draw in the refrigerant from the can.

After adding one can of refrigerant, post the gage readings - you want the reading right before the compressor cycles off. For the low side, it will be the lowest reading and the high side, it will be the highest reading. Also feel the evaporator oulet line to see if it is cold.

[Brobichaud]

Thank you again for a detailed response.

Southern Florida - Relative Humidity is 75% @ 11:30 AM. Earlier it was 90%.

System sucked in one can of refrigerant.

Static: Low side = 60 psi., High side = 65 psi. Temp remains 76 deg.

Operating: Low side = 34 - 40. High side = 135 - 165.

Both evap lines are now same temperature. Vents are blowing cold.

I am guessing it is still a little low on refrigerant. Maybe time will tell if the system is leaking ???

Thanks, Bob

[KHE]

What are the vent temps. at the center outlet when the climate control is set to 60°?

The range in pressures you posted - I assume the compressor kicks off at 34 psi on the low side and about 165 psi on the high side? It sounds like you have it about right. The vent temperature would be helpful to know. You do not want to overcharge it or the cooling performance will go down.

There is probably a slow leak in the system - If it were my car, I'd run it and monitor the A/C performance. If it starts blowing warm air, you know there is a leak in the system. Check the condenser (mounted in front of the radiator) for wet/oily spots as well as all the connections on the hoses/lines.